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Per device dirty throttling patches These patches aim to improve balance_dirty_pages() and directly address three issues: 1) inter device starvation 2) stacked device deadlocks 3) inter process starvation 1 and 2 are a direct result from removing the global dirty limit and using per device dirty limits. By giving each device its own dirty limit is will no longer starve another device, and the cyclic dependancy on the dirty limit is broken. In order to efficiently distribute the dirty limit across the independant devices a floating proportion is used, this will allocate a share of the total limit proportional to the device's recent activity. 3 is done by also scaling the dirty limit proportional to the current task's recent dirty rate. Changes since -v7: - perpcu_counter renames (partially suggested by Linus) - percpu_counter error handling - bdi_init error handling - fwd port to .23-rc1-mm --- # # cleanups # nfs_congestion_fixup.patch # # percpu_counter rework # percpu_counter_add.patch percpu_counter_batch.patch percpu_counter_add64.patch percpu_counter_set.patch percpu_counter_sum_positive.patch percpu_counter_sum.patch percpu_counter_init.patch percpu_counter_init_irq.patch # # per BDI dirty pages # bdi_init.patch bdi_init_container.patch bdi_init_mtd.patch mtd-bdi-fixups.patch bdi_mtdconcat.patch bdi_stat.patch bdi_stat_reclaimable.patch bdi_stat_writeback.patch bdi_stat_sysfs.patch # # floating proportions # proportions.patch proportions_single.patch # # per BDI dirty # writeback-balance-per-backing_dev.patch dirty_pages2.patch # # debug foo # bdi_stat_debug.patch -
Ok, the patches certainly look pretty enough, and you fixed the only thing I complained about last time (naming), so as far as I'm concerned it's now just a matter of whether it *works* or not. I guess being in -mm will help somewhat, but it would be good to have people with several disks etc actively test this out. Linus -
There are positive reports in the never-ending "my system crawls like an XT when copying large files" bugzilla entry: http://bugzilla.kernel.org/show_bug.cgi?id=7372 " vfs_cache_pressure=1 TCQ nr_requests 8 128 not that bad 1 128 snappiest configuration, almost no pauses (or unnoticable ones) " " 1) vfs_cache_pressure at 100, 2.6.21.5+per bdi throttling patch Result is good, not as snappier as I'd want during a large copy but still usable. No process seems stuck for agen, but there seems to be some short (second or subsecond) moment where everything is stuck (like if you run a top d 0.5, the screen is not updated on a regular basis). 2) vfs_cache_pressure at 1, 2.6.21.5+per bdi throttling patch Result is at 2.6.17 level. It is the better combination since 2.6.17. " " 1) I've applied the patches posted by Peter Zijlstra in comment #76 to the 2.6.21-mm2 kernel to check if it removes the problem. My impression is that the problem is still there with those patches, although less visible then with the clean 2.6.21 kernel. " so the whole problem area seems to be a "perfect storm" created by a combination of TCQ, IO scheduling and VM dirty handling weaknesses. Per device dirty throttling is a good step forward and it makes a very visible positive difference. Ingo -
i forgot this entry: " We recently upgraded our office to gigabit Ethernet and got some big AMD64 / 3ware boxes for file and vmware servers... only to find them almost useless under any kind of real load. I've built some patched 2.6.21.6 kernels (using the bdi throttling patch you mentioned) to see if our various Debian Etch boxes run better. So far my testing shows a *great* improvement over the stock Debian 2.6.18 kernel on our configurations. " and bdi has been in -mm in the past i think, so we also know (to a certain degree) that it does not hurt those workloads that are fine either. [ my personal interest in this is the following regression: every time i start a large kernel build with DEBUG_INFO on a quad-core 4GB RAM box, i get up to 30 seconds complete pauses in Vim (and most other tasks), during plain editing of the source code. (which happens when Vim tries to write() to its swap/undo-file.) ] Ingo -
I have an issue that sounds like it's related. I've got a syslog server that's got two Opteron 246 cpu's, 16G ram, 2x140G 15k rpm drives (fusion MPT hardware mirroring), 16x500G 7200rpm SATA drives on 3ware 9500 cards (software raid6) running 2.6.20.3 with hz set at default and preempt turned off. I have syslog doing buffered writes to the SCSI drives and every 5 min a cron job copies the data to the raid array. I've found that if I do anything significant on the large raid array that the system looses a significant amount of the UDP syslog traffic, even though there should be pleanty of ram and cpu (and the spindles involved in the writes are not being touched), even a grep can cause up to 40% losses in the syslog traffic. I've experimented with nice levels (nicing down the grep and nicing up the syslogd) without a noticable effect on the losses. I've been planning to try a new kernel with hz=1000 to see if that would help, and after that experiment with the various preempt settings, but it sounds like the per-device queues may actually be more relavent to the problem. what would you suggest I test, and in what order and combination? David Lang -
(adding netdev cc:) At least on a surface level, your report has some similarities to http://lkml.org/lkml/2007/5/21/84 . In that message, John Miller mentions several things he tried without effect: < - I increased the max allowed receive buffer through < proc/sys/net/core/rmem_max and the application calls the right < syscall. "netstat -su" does not show any "packet receive errors". < < - After getting "kernel: swapper: page allocation failure. < order:0, mode:0x20", I increased /proc/sys/vm/min_free_kbytes < < - ixgb.txt in kernel network documentation suggests to increase < net.core.netdev_max_backlog to 300000. This did not help. < < - I also had to increase net.core.optmem_max, because the default < value was too small for 700 multicast groups. As they're all pretty simple to test, it may be worthwhile to give them a shot just to rule things out. Ray -
I will try them later today. I forgot to mention that the filesystems are ext2 for the mirrored high speed disks and xfs for the 8TB array. David Lang -
mercury1:/proc/sys/net/core# cat rmem_*
124928
131071
mercury1:/proc/sys/net/core# netstat -su
Udp:
697853177 packets received
10025642 packets to unknown port received.
191726680 packet receive errors
63194 packets sent
RcvbufErrors: 191726680
UdpLite:
mercury1:/proc/sys/net/core# cat netdev_*
300
1000
unfortunantly the load is not high enough right now to see a real
difference (it's only doing ~1400 logs/sec) I'll catch it at a higher load
point to see if these make any difference.
-
hm, it turns out that it's due to vim doing an occasional fsync not only on writeout, but during normal use too. "set nofsync" in the .vimrc solves this problem. Ingo -
Yes, that's independent. The fact is, ext3 *sucks* at fsync. I hate hate hate it. It's totally unusable, imnsho. The whole point of fsync() is that it should sync only that one file, and avoid syncing all the other stuff that is going on, and ext3 violates that, because it ends up having to sync the whole log, or something like that. So even if vim really wants to sync a small file, you end up waiting for megabytes of data being written out. I detest logging filesystems. Linus -
yeah, it's really ugly. But otherwise i've got no real complaint about ext3 - with the obligatory qualification that "noatime,nodiratime" in /etc/fstab is a must. This speeds up things very visibly - especially when lots of files are accessed. It's kind of weird that every Linux desktop and server is hurt by a noticeable IO performance slowdown due to the constant atime updates, while there's just two real users of it: tmpwatch [which can be configured to use ctime so it's not a big issue] and some backup tools. (Ok, and mail-notify too i guess.) Out of tens of thousands of applications. So for most file workloads we give Windows a 20%-30% performance edge, for almost nothing. (for RAM-starved kernel builds the performance difference between atime and noatime+nodiratime setups is more on the order of 40%) Ingo -
Not just more IO: it will cause great gobs of blockdev pagecache to remain -
i tried to convince distro folks about it ... but there's fear, uncertainty and doubt about touching /etc/fstab and i suspect no major distro will do it until another does it - which is a catch-22 :-/ So i guess we should add a kernel config option that allows the kernel rpm maker to just disable atime by default. (re-enableable via boot-line and fstab entry too) [That new kernel config option would be disabled by default.] That makes it much easier to control and introduce. Ingo -
It makes it much more messy and awkward as the same system behaves in arbitary different ways under different builds of the kernel. If you want to sort this in Fedora for example you just need to package and announce a desktop-tuning rpm which makes the relevant updates on install and reverses them on remove. Stick the scheduler/vm tuning values in as well and the disk queue tweaks. Regardless of the kernel defaults people will install such a package en-mass... Alan -
Just curious - do you have numbers with relatime? -
nope. Stupid question, i just tried it and got this: EXT3-fs: Unrecognized mount option "relatime" or missing value i've got util-linux-2.13-0.46.fc6 and 2.6.22 on that box, shouldnt that be recent enough? As far as i can see it from the kernel-side code, this works on the general VFS level and hence should be supported by ext3 already. even relatime means one extra write IO after a file has been created, but at least for read-mostly files it avoids the continuous atime update. Ingo -
Mmmh, "mount -o remount,noatime /" seems to Work For Me in Ubuntu with util-linux/mount "2.12r-17ubuntu"...but then Google says [1] that Ubuntu has been shipping with relatime enabled as default for months, so it's probably patched (probably only in the kernel). So maybe upstream util-linux hasn't merged the relatime patch. [1]: http://lkml.org/lkml/2007/2/12/30 -
^^^^^ Obviously, i meant "noatime"...(so it's unlikely that ubuntu has patched -
The relatime patch has been applied to util-lilnux-ng-2.13 (now -rc3),
you will see it in Fedora 8 (and probably in the others distros).
Karel
--
Karel Zak <kzak@redhat.com>
-
I agree, we really should do something about atime. But the fsync thing is a real issue. It literally makes ext3 almost unusable from a latency standpoint on many loads. I have a fast disk, and don't actually tend to have all that much going on normally, and it still hurts occasionally. One of the most common (and *best*) reasons for using fsync is for the mail spool. So anybody that uses local email will actually be doing a lot of fsync, and while you could try to thread the interfaces, I don't think a lot of mailers do. So fsync ends up being a latency issue for something that a lot of people actually see, and something that you actually end up working with and you notice the latencies very clearly. Your editor auto-save feature is another good example of that exact same thing: the fsync actually is there for a very good reason, even if you apparently decided that you'd rather disable it. But yeah, "noatime,data=writeback" will quite likely be *quite* noticeable (with different effects for different loads), but almost nobody actually runs that way. I ended up using O_NOATIME for the individual object "open()" calls inside git, and it was an absolutely huge time-saver for the case of not having "noatime" in the mount options. Certainly more than your estimated 10% under some loads. The "relatime" thing that David mentioned might well be very useful, but it's probably even less used than "noatime" is. And sadly, I don't really see that changing (unless we were to actually change the defaults inside the kernel). Linus -
I actually vote for that. IMO, distros should turn -on- atime updates when they know its needed. Jeff -
If you mean "relatime" I concur. "noatime" hurts mutt and others while "relatime" has no known problems, afaics. Jörn -- Joern's library part 5: http://www.faqs.org/faqs/compression-faq/part2/section-9.html -
so ... one app can keep 30,000+ apps hostage? i use Mutt myself, on such a filesystem: /dev/md0 on / type ext3 (rw,noatime,nodiratime,user_xattr) and i can see no problems, it notices new mails just fine. Ingo -
Given the choice between only "atime" and "noatime" I'd agree with you. Heck, I use it myself. But "relatime" seems to combine the best of both worlds. It currently just suffers from mount not supporting it in any relevant distro. Jörn -- Joern's library part 2: http://www.art.net/~hopkins/Don/unix-haters/tirix/embarrassing-memo.html -
And here is a completely untested patch to enable it by default. Ingo, can you see how good this fares compared to "atime" and "noatime,nodiratime"? Jörn -- Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it. -- Brian W. Kernighan --- linux-2.6.22_relatime/fs/namespace.c~default_relatime 2007-05-16 02:01:39.000000000 +0200 +++ linux-2.6.22_relatime/fs/namespace.c 2007-08-04 21:36:20.000000000 +0200 @@ -1401,6 +1401,10 @@ long do_mount(char *dev_name, char *dir_ if (data_page) ((char *)data_page)[PAGE_SIZE - 1] = 0; +#ifdef CONFIG_DEFAULT_RELATIME + flags |= MS_RELATIME; +#endif + /* Separate the per-mountpoint flags */ if (flags & MS_NOSUID) mnt_flags |= MNT_NOSUID; --- linux-2.6.22_relatime/fs/Kconfig~default_relatime 2007-05-16 02:01:38.000000000 +0200 +++ linux-2.6.22_relatime/fs/Kconfig 2007-08-04 21:39:46.000000000 +0200 @@ -6,6 +6,15 @@ menu "File systems" if BLOCK +config DEFAULT_RELATIME + bool "Mount all filesystems with 'relatime' by default" + default y + help + Relatime only updates atime once after any file has been changed. + Setting this should give a noticeable performance bonus. + + If unsure, say Y. + config EXT2_FS tristate "Second extended fs support" help -
Umm, no f**king way. atime selection is 100% policy and belongs into userspace. Add to that the problem that we can't actually re-enable atimes because of the way the vfs-level mount flags API is designed. Instead of doing such a fugly kernel patch just talk to the handfull of distributions that matter to update their defaults. -
We already tried that here. The response: "If noatime is so great, why isn't it the default in the kernel?" -
Yes, and around and around we go :/ Jeff -
Ok so we have a pile of people @redhat.com sitting on linux-kernel complaining about Red Hat distributions not taking it up. Guys - can we just fix it internally please like sensible folk ? Ingo's latest 'not quite noatime' seems to cure mutt/tmpwatch so it might finally make sense to do so. Alan -
Do we report max(ctime, mtime) as the atime by default when noatime is set or do we still need that to be done? -
noatime is unchanged by my patch (it is not the same as the 'improved relatime' mode my patch activates), but it would make sense to do your change, independently. Ingo -
From what I've seen the problem seems to be that the inode gets marked dirty when we update atime. Why isn't this easily fixable by just adding an additional dirty flag that says atime has changed? Then we only cause a write when we remove the inode from the inode cache, if only atime is updated. Unlike relatime, there's no user-visible change (unless the machine crashes without clean unmount, but not sure anyone cares that much about that cornercase). Atime changes are thus kept in-ram until umount / inode reclaim. -
On Wed, 08 Aug 2007 14:10:15 -0700 I think that could be made to work, and it would fix the performance issue. It is a behaviour change. At present ext3 (for example) commits everything every five seconds. After a change like this, a crash+recovery could cause a file's atime to go backwards by an arbitrarily large time interval - it could easily be months. -
A second pdflush / workqueue at a slower rate would alleviate that. Yes, it's a semantic change ... but only in an incredibly small corner-case ? -
This becomes delayed atime writes. I'm not sure that it's better to batch up the writes and do them all in one big seeky go, or to trickle them out as they are done. Best of all is not to do them at all. Note when talking about saving up atime updates to write out that the final write is going to be sloooooow. Inodes are typically 128 bytes, and you may have to do a seek between every one. Currents disks can do on the order of 100 seeks a second. So do a find on 1000 files and you've just created 10 seconds of I/O hanging out in memory. -VAL -
I would think that (really) updating atime on open would be enough, hopefully without being too much. The "lazyatime" thing I was playing with only updated on open, final close, write, and fork. I like the idea of updating once in a while, but one of the benefits of noatime is allowing drives to spin down via inactivity. If something does get done in the area of less but non-zero atime tracking, perhaps that could be taken into account. I have to check what "laptop_mode actually does, since my laptops are old installs. -- Bill Davidsen <davidsen@tmr.com> "We have more to fear from the bungling of the incompetent than from the machinations of the wicked." - from Slashdot -
Indeed. Just change /bin/mount so it defaults to "noatime" unless there is an explicit "atime". Similiar for diratime. Problem solved. Helge Hafting -
Well, we could make it the default for the kernel (possibly under a "fast-atime" config option), and then people can add "atime" or "noatime" as they wish, since mount has supported _those_ options for a long time. Linus -
Side note: while I think the fsync() behaviour is more irritating than atime, that one is harder to fix. I think it's reasonable to have "relatime" as a default strategy for the kernel, but I don't think it's necessarily at all as reasonable to change a filesystem-specific ordering constraint. Linus -
the patch below implements this, but there's a problem: we only have MNT_NOATIME, we have no MNT_ATIME option AFAICS. So there's no good way to detect it when a user _does_ want to have atime :-( Perhaps a boot option to turn this off? [sucks a bit but keeps the solution within the kernel.] Ingo ---------------------------------> Subject: [patch] add CONFIG_FASTATIME From: Ingo Molnar <mingo@elte.hu> add the CONFIG_FASTATIME kernel option, which makes "relatime" the default for all mounts. Signed-off-by: Ingo Molnar <mingo@elte.hu> --- fs/Kconfig | 10 ++++++++++ fs/namespace.c | 4 ++++ 2 files changed, 14 insertions(+) Index: linux/fs/Kconfig =================================================================== --- linux.orig/fs/Kconfig +++ linux/fs/Kconfig @@ -2060,6 +2060,16 @@ config 9P_FS endmenu +config FASTATIME + bool "Fast atime support by default" + default y + help + If you say Y here, all your filesystems that do not have + the "noatime" or "atime" mount option specified will get + the "relatime" option by default, which speeds up atime + updates. (atime will only be updated if ctime or mtime + is more recent than atime) + if BLOCK menu "Partition Types" Index: linux/fs/namespace.c =================================================================== --- linux.orig/fs/namespace.c +++ linux/fs/namespace.c @@ -1409,6 +1409,10 @@ long do_mount(char *dev_name, char *dir_ mnt_flags |= MNT_NODIRATIME; if (flags & MS_RELATIME) mnt_flags |= MNT_RELATIME; +#ifdef CONFIG_FASTATIME + if (!(flags & (MNT_NOATIME | MNT_NODIRATIME))) + mnt_flags |= MNT_RELATIME; +#endif flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE | MS_NOATIME | MS_NODIRATIME | MS_RELATIME); -
btw., "relatime" does not seem to make much of a difference, if i do
this:
ls -l x ; sync
on a "relatime" mounted filesystem ('x' is a regular file), then there's
disk IO for every such command. Only if i mount it noatime,nodiratime do
i get zero disk IO. Or my patch is wrong somehow.
Ingo
-
here's an updated patch that implements a full spectrum of config, boot and sysctl parameters to make it easy for users and distros to make noatime the default. Tested on ext3, with and without atime. for compatibility reasons the config option defaults to disabled, so this patch has no impact by default. If CONFIG_DEFAULT_NOATIME is enabled for a kernel then all filesystems will be noatime mounted. The boot and sysctl options are available unconditionally. Ingo ----------------------------> Subject: [patch] add noatime/atime boot options, CONFIG_DEFAULT_NOATIME From: Ingo Molnar <mingo@elte.hu> add the "noatime" (and "atime") boot options to enable/disable atime updates for all filesystems. also add the CONFIG_DEFAULT_NOATIME kernel option (disabled by default for compatibility reasons), which makes "noatime" the default for all mounts without an extra kernel boot option. also add the /proc/sys/kernel/mount_with_atime flag which can be changed runtime to modify the behavior of subsequent new mounts. Signed-off-by: Ingo Molnar <mingo@elte.hu> --- Documentation/kernel-parameters.txt | 12 +++++++ fs/Kconfig | 21 +++++++++++++ fs/namespace.c | 56 ++++++++++++++++++++++++++++++++++++ include/linux/mount.h | 2 + kernel/sysctl.c | 9 +++++ 5 files changed, 100 insertions(+) Index: linux/Documentation/kernel-parameters.txt =================================================================== --- linux.orig/Documentation/kernel-parameters.txt +++ linux/Documentation/kernel-parameters.txt @@ -303,6 +303,12 @@ and is between 256 and 4096 characters. atascsi= [HW,SCSI] Atari SCSI + atime [FS] default to enabled atime updates on all + filesystems. + + atime= [FS] default to enabled/disabled atime updates on all + filesystems. + atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, EzKey and similar keyboards @@ ...
there is another trick possible (more involved though, Al will have to jump in on that one I suspect): Have 2 types of "dirty inode" states; one is the current dirty state (meaning the full range of ext3 transactions etc) and "lighter" state of "atime-dirty"; which will not do the background syncs or journal transactions (so if your machine crashes, you lose the atime update) but it does keep atime for most normal cases and keeps it standard compliant "except after a crash". -
That would make us standards compliant (POSIX explicitly says that what happens after a unclean shutdown is Unspecified) and it would make things a heck of a lot faster. However, there is a potential problem which is that it will keep a large number of inodes pinned in memory, which is its own problem. So there would have to be some way to force the atime updates to be merged when under memory pressure, and and perhaps on some much longer background interval (i.e., every hour or so). - Ted -
on the journalling side this would be one transaction (not 5 milion) and... since inodes are grouped on disk, you can even get some better coalescing this way... Wonder if we could do inode-grouping smartly; eg if we HAVE to write inode X, also write out the atime-dirty inodes in range X-Y to X+Y (where Y is some tunable) in the same IO.. -- if you want to mail me at work (you don't), use arjan (at) linux.intel.com Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org -
We already have filesystems in the tree that do such advances things as inode writeback clustering for more than ten years :) -
In some setups it will and in others it won't. Nor is it the only application that has this requirement. Ext3 currently is a standards compliant file system. Turn off atime and its very non standards compliant, turn to relatime and its not standards compliant but nobody will break (which is good) Either change is a big user/kernel interface change and no major vendor targets desktop as primary market so I'm not suprised they haven't done this. The fix is to educate them further not to break the kernel. There are several reasons for that - Distros will change the least conservative stuff first so we have the dedicated followers of fashion finding problems first - Existing systems won't suddenly change behaviour and break (and as the catastrophic failure case is backup failure we do not want to break them) People just need to know about the performance differences - very few realise its more than a fraction of a percent. I'm sure Gentoo will use relatime the moment anyone knows its > 5% 8) Alan -
Linux has always been a "POSIX unless its stupid" type of system. For the upstream kernel, we should do the right thing -- noatime by default -- but allow distros and people that care about rigid compliance to easily change the default. <chuckle> Sounds like an effective idea :) Though strictly in the context of atime vs. noatime, servers benefit from that too, not just desktop. Jeff -
Linux has never been a "suprise your kernel interfaces all just changed today" kernel, nor a "gosh you upgraded and didn't notice your backups broke" kernel. -
Can you give examples of backup solutions that rely on atime being updated? I can understand backup tools using mtime/ctime for incremental backups (like tar + Amanda, etc), but I'm having trouble figuring out why someone would want to use atime for that. Best regards Claudio -
HSM is the usual one, and to a large extent probably why Unix originally had atime. Basically migrating less used files away so as to keep the system disks tidy. Its not something usally found on desktop boxes so it doesn't in anyway argue against the distribution using noatime or relative atime, but on big server boxes it matters -
atime is used as a _hint_, at most and HSM sure works just fine on an atime-incapable filesystem too. So it's the same deal as "add user_xattr mount option to the filesystem to make Beagle index faster". It's now: "if you use HSM storage add the atime mount option to make it slightly more intelligent. Expect huge IO slowdowns though." The only remotely valid compatibility argument would be Mutt - but even that handles it just fine. (we broke way more software via noexec) Ingo -
I find it pretty normal to use tmpreaper to clear out unused files from certain types of semi-temporary directory structures. Those files are often only ever read. They'd start randomly disappearing while in use. But then again, maybe I'm the only guy on the planet who uses tmpreaper. -- / jakob -
And went through a sensible process of resolving it. And its not just mutt. HSM stuff stops working which is a big deal as stuff clogs up. The /tmp/ cleaning tools go wrong as well. These are big deals because you seem intent on using a large hammer to force a change that should be done properly by other means. The /tmp cleaning for example can probably be done other ways in future but the changes should be in place first. -
what OSS HSM software stops working and what is its failure mode? /tmp
cleaning tools will work _just fine_ if we report back max(mtime,ctime)
as atime - they'll zap more /tmp stuff as they used to. There's no
guarantee for /tmp contents anyway if tmpwatch is running. Or the patch
below.
Ingo
--- /etc/cron.daily/tmpwatch.orig 2007-08-05 14:44:25.000000000 +0200
+++ /etc/cron.daily/tmpwatch 2007-08-05 14:45:10.000000000 +0200
@@ -1,9 +1,9 @@
#! /bin/sh
-/usr/sbin/tmpwatch -x /tmp/.X11-unix -x /tmp/.XIM-unix -x /tmp/.font-unix \
+/usr/sbin/tmpwatch --mtime -x /tmp/.X11-unix -x /tmp/.XIM-unix -x /tmp/.font-unix \
-x /tmp/.ICE-unix -x /tmp/.Test-unix 10d /tmp
-/usr/sbin/tmpwatch 30d /var/tmp
+/usr/sbin/tmpwatch --mtime 30d /var/tmp
for d in /var/{cache/man,catman}/{cat?,X11R6/cat?,local/cat?}; do
if [ -d "$d" ]; then
- /usr/sbin/tmpwatch -f 30d "$d"
+ /usr/sbin/tmpwatch --mtime -f 30d "$d"
fi
done
-
Ingo, In your example above, maybe it's the opposite, users know they can keep a file in /tmp one more week by simply cat'ing it. Changing the kernel in a non-easily reversible way is not kind to the users. As you pointed it, there's no "atime" option in mount, and quite frankly, having to reboot an NFS server to change a command line option which should belong to fstab is quite gross. And yes, there may be people realying on atime in specific environments. I remember having used it in the past to automatically archive unused files. Those people might not be affected by the drop in performance at all and would rather keep the feature. I like Alan's idea of a package to automatically add "noatime" everywhere in fstab, not only because it's easy to use, but because it will also teach users how they can proceed on their other systems. Also, if you make the package yourself, it will benefit from the "coolness factor" many people see in everything that's done by renown persons (you know, the type of people who regularly ask you if you use vi/emacs and what type of window manager, and who then consider it must be good if you use it). I'll stop ranting here, some of them may be reading ;-) As a second step, once many people explicitly ask for "noatime" by default, it will be time to add MS_ATIME to the kernel and to mount, and set NOATIME as the default with big warnings. This will make everyone happy. But expecting the admins to recompile their kernels or to reboot to change the atime status is not acceptable IMHO. Moreover, they will not even know they have to do this and they will feel frustrated because the system will not do what they want. I've already been bothered a lot by ext3 filesystems with dirindex enabled. When you boot from an old CD and you cannot mount them, it's already quite irritating (not to mention that tune2fs from the old CD does not know about it either so you cannot disable the option). But it's even worse when you plug an USB hard disk into an old ...
sure - and i'm not arguing that noatime should the kernel-wide default. In every single patch i sent it was a .config option (and a boot option _and_ a sysctl option that i think you missed) that a user/distro enables or disabled. But i think the /tmp argument is not very strong: /tmp is fundamentally volatile, and you can grow dependencies on pretty much _any_ aspect of the kernel. So the question isnt "is there impact" (there is, at least for noatime), the question is "is it still worth none of my patches did any of that... anyway, my latest patch doesnt do noatime, it does the "more intelligent relatime" approach. Ingo -
I did not notice you talked about a sysctl. A sysctl provides the ability to switch the behaviour without rebooting, while both the config option ... which is not equivalent noatime in the initial example. Regards, Willy -
In addition, big server boxes are usually not reading a huge *number* of files per second. The place where you see this as a problem is (a) compilation, thanks to huge /usr/include hierarchies (and here things have gotten worse over time as include files have gotten much more complex than in the early Unix days), and (b) silly desktop apps that want to scan huge numbers of XML files or who want to read every single image file on the desktop or in an open file browser window to show c00l icons. Oh, and I guess I should include Maildir setups. If you are always reading from the same small set of files (i.e., a database workload), then those inodes only get updated every 5 seconds (the traditional/default metadata update sync time, as well as the default ext3 journal update time), it's no big deal. Or if you are running a mail server, most of the time the mail queue files are getting updated anyway as you process them, and usually the mail is delivered before 5 seconds is up anyway. So earlier, when Ingo characterized it as, "whenever you read from a file, even one in memory cache.... do a write!", it's probably a bit unfair. Traditional Unix systems simply had very different workload characteristics than many modern dekstop systems today. - Ted -
yeah, i didnt mean to say that it is _always_ a big issue, but "only a small number of files are read" is a very, very small minority of even the database server world. Ingo -
OTOH, consider a popular Linux task, web serving. atime results in a lot of unnecessary disk traffic. Jeff -
it's a big, noticeable effect on 99% of the Linux boxes. Ingo -
it's just one of those things that get compounded with journaling filesystems though..... a single async write that happens "sometime in the future" is one thing... having a full transaction (which acts as barrier and synchronisation point) is something totally worse. -- if you want to mail me at work (you don't), use arjan (at) linux.intel.com Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org -
Programs which migrate unused files or delete them are the usual cases. -- Bill Davidsen <davidsen@tmr.com> "We have more to fear from the bungling of the incompetent than from the machinations of the wicked." - from Slashdot -
HSM uses atime as a _hint_. The only even remotely valid argument is Mutt, and even that one could easily be fixed _it is not even installed by default on most distros_ and nobody but me uses it ;) [and i've been using Mutt on noatime filesystems for years] So basically a single type of package and use-case (against tens of thousands of packages) held all of Linux desktop IO performance hostage for 10 years, to the tune of a 20-30-50-100% performance degradation (depending on the workload)? Wow. And the atime situation is _so_ obvious, what will we do in the much less obvious cases? Ingo -
However, relatime has the POSIX behavior without the overhead. Therefore that (and maybe reldiratime?) are a far better choice. I don't see a big problem with some version of utils not supporting it, since it can be in the kernel and will be in the utils soon enough. We have lived without it this long, sounds as if we could live a bit longer. -- Bill Davidsen <davidsen@tmr.com> "We have more to fear from the bungling of the incompetent than from the machinations of the wicked." - from Slashdot -
> However, relatime has the POSIX behavior without the overhead. Therefore No. relatime has approximately SuS behaviour. Its not the same as "correct" behaviour. -
Actually correct, but in terms of what can or does break, relatime seems a lot closer than noatime, I can't (personally) come up with any scenario where real applications would see something which would change behavior adversely. Making noatime a default in the kernel requiring a boot option to restore current behavior seems to be a turn toward the "it doesn't really work right but it's *fast*" model. If vendors wanted noatime they are smart enough to enable it. Now with relatime giving most of the benefits and few (of any) of the side effects, I would expect a change. By all means relatime by default in FC8, but not noatime, and let those who find some measurable benefit from noatime use it. -- Bill Davidsen <davidsen@tmr.com> "We have more to fear from the bungling of the incompetent than from the machinations of the wicked." - from Slashdot -
earlier in the thread it was claimed that Ubuntu is now defaulting to noatime+nodiratime, and has done so for several months. Could be one of the reasons why: noatime,nodiratime gave 50% of wall-clock kernel rpm build performance improvement for Dave Jones, on a beefy box. Unless i misunderstood what you meant under 'fraction of a percent' your numbers are _WAY_ off. Atime updates are a _huge everyday deal_, from laptops to servers. Everywhere on the planet. Give me a Linux desktop anywhere and i can tell you whether it has atimes on or off, just by clicking around and using apps (without looking at the mount options). That's how i notice it that i forgot to turn off atime on any newly installed system - the come on! Any standards testsuite needs tons of tweaks to the system to run through to completion. Mounting the filesystem atime will just be one more item in the long list of (mostly silly) 'needed for standards compliance' items (most of which nobody configures). What matters are the apps, and nary any app depends on atime, and those people who depend on them can turn on atime just fine. (it's the same as for extended attributes for example - and attributes are infinitely _more_ useful than atime.) Ingo -
it's also a Watt or so of power if you have the AHCI ALPM patches in the kernel (which are pending mainline inclusion)... -
i cannot over-emphasise how much of a deal it is in practice. Atime
updates are by far the biggest IO performance deficiency that Linux has
today. Getting rid of atime updates would give us more everyday Linux
performance than all the pagecache speedups of the past 10 years,
_combined_.
it's also perhaps the most stupid Unix design idea of all times. Unix is
really nice and well done, but think about this a bit:
' For every file that is read from the disk, lets do a ... write to
the disk! And, for every file that is already cached and which we
read from the cache ... do a write to the disk! '
tell that concept to any rookie programmer who knows nothing about
kernels and the answer will be: 'huh, what? That's gross!'. And Linux
does this unconditionally for everything, and no, it's not only done on
some high-security servers that need all sorts of auditing enabled that
logs every file read - no, it's done by 99% of the Linux desktops and
servers. For the sake of some lazy mailers that could now be using
inotify, and for the sake of ... nothing much, really - forensics
software perhaps.
Ingo
-
Think about the user for a moment instead. Do things right. The job of the kernel is not to "correct" for distribution policy decisions. The distributions need to change policy. You do that by showing the distributions the numbers. With a Red Hat on if we can move from /dev/hda to /dev/sda in FC7 then we can move from atime to noatime by default on FC8 with appropriate release note warnings and having a couple of betas to find out what other than mutt goes boom. -
btw., Mutt does not go boom, i use it myself. It works just fine and notices new mails even on a noatime,nodiratime filesystem. Ingo -
noatime is a superset of nodiratime, btw. -
heh, indeed. I've been using this trick for 10 years on my desktops so it's an ancient thinko :) Ingo -
IIRC, atime is used by mailers and by the shell to detect that new mail has arrived and report it only once if there are several intances watching the same mbox. I too use mutt and noatime,nodiratime everywhere (same 10 year-old thinko), and the only side effect is that when I have a new mail, it is reported in all of my xterms until I read it, clearly something I can live with (and sometimes it's even desirable). In fact, mutt is pretty good at this. It updates atime and ctime itself as soon as it opens the mbox, so the shell is happy and only reports "you have mail" afterwards. Well, I hope we're not getting too much off-topic here... Willy -
For me mutt fails to recognize new mail. And the difference might be this: http://www.google.de/search?q=enable-buffy-size Jörn -- Fancy algorithms are slow when n is small, and n is usually small. Fancy algorithms have big constants. Until you know that n is frequently going to be big, don't get fancy. -- Rob Pike -
Like a greased penguin. I had to reboot with my ugly patch posted earlier in the patch to actually test it, though. Relatime suffers from a distribution problem, nothing else. Guess I should throw in a kernel compile test as well, just to get a feel for the performance. Jörn -- Homo Sapiens is a goal, not a description. -- unknown -
Three runs each of noatime, relatime and atime, both with cold caches and with warm caches. Scripts below. Run on a Thinkpad T40, 1.5GHz, 2GiB RAM, 60GB 2.5" IDE disk, ext3. Biggest difference between atime and noatime (median run, cold cache) is ~2.3%, nowhere near the numbers claimed by Ingo. Ingo, how did you measure 10% and more? noatime, cold cache relatime, cold cache atime, cold cache real 2m10.242s real 2m10.549s real 2m10.388s user 1m46.886s user 1m46.680s user 1m47.000s sys 0m8.243s sys 0m8.423s sys 0m8.239s real 2m11.270s real 2m11.212s real 2m14.280s user 1m46.940s user 1m46.776s user 1m46.670s sys 0m8.139s sys 0m8.283s sys 0m8.503s real 2m11.601s real 2m14.861s real 2m14.335s user 1m46.920s user 1m47.103s user 1m46.846s sys 0m8.246s sys 0m8.266s sys 0m8.349s noatime, warm cache relatime, warm cache atime, warm cache real 1m55.894s real 1m56.053s real 1m56.905s user 1m46.683s user 1m46.600s user 1m46.853s sys 0m8.186s sys 0m8.349s sys 0m8.249s real 1m55.823s real 1m56.093s real 1m57.077s user 1m46.583s user 1m46.913s user 1m46.590s sys 0m8.259s sys 0m7.966s sys 0m8.523s real 1m55.789s real 1m56.214s real 1m57.224s user 1m46.803s user 1m46.753s user 1m46.953s sys 0m8.053s sys 0m8.113s sys 0m8.113s Jörn -- Data expands to fill the space available for storage. -- Parkinson's Law Cold cache script: #!/bin/sh make distclean echo 1 > /proc/sys/vm/drop_caches echo 2 > /proc/sys/vm/drop_caches echo 3 > /proc/sys/vm/drop_caches make allnoconfig time make Warm cache script: #!/bin/sh make distclean make allnoconfig rgrep ...
Ingo had CONFIG_DEBUG_INFO=y, which generates heaps more writeout, but no additional atime updates. Ingo had a faster computer ;) That will generate many more MB/sec write traffic, so the cost of those atime seeks becomes proportionally higher. Basically: you're CPU-limited, Ingo is seek-limited. -
Configuration dependant, and also mutt and the shell will misreport new mail with noatime on the mail spool. The shell should probably use inotify of course but that change has to be made. -
just to quote from this same email thread: | I too use mutt and noatime,nodiratime everywhere (same 10 year-old | thinko), and the only side effect is that when I have a new mail, it | is reported in all of my xterms until I read it, clearly something I | can live with (and sometimes it's even desirable). | | In fact, mutt is pretty good at this. It updates atime and ctime | itself as soon as it opens the mbox, so the shell is happy and only | reports "you have mail" afterwards. Ingo -
On Sun, Aug 05, 2007 at 09:21:41AM +0200, Ingo Molnar wrote: > * Alan Cox <alan@lxorguk.ukuu.org.uk> wrote: > > > With a Red Hat on if we can move from /dev/hda to /dev/sda in FC7 then > > we can move from atime to noatime by default on FC8 with appropriate > > release note warnings and having a couple of betas to find out what > > other than mutt goes boom. > > btw., Mutt does not go boom, i use it myself. It works just fine and > notices new mails even on a noatime,nodiratime filesystem. It still fails miserably for me. If I hit 'C' and '?' I get a list of my mail folders, with some of them marked 'N' if they have new mail. Without atime, those N's never show up and every mbox looks like it has no new mail. Dave -- http://www.codemonkey.org.uk -
This is true for one using mbox_type=mbox (i.e unix native mailbox format). Maildir type should work just fine as mutt will noticed that new mail has arrived on 'new' subdir (according to maildir spec). Then yes, it is configuration dependent. Regards, P.Y. Adi Prasaja -
does it work with the "atime on steroids" patch below? (no need to configure anything, just apply the patch and go.) Ingo -----------------------> Subject: [patch] [patch] implement smarter atime updates support From: Ingo Molnar <mingo@elte.hu> change relatime updates to be performed once per day. This makes relatime a compatible solution for HSM, mailer-notification and tmpwatch applications too. also add the CONFIG_DEFAULT_RELATIME kernel option, which makes "norelatime" the default for all mounts without an extra kernel boot option. add the "default_relatime=0" boot option to turn this off. also add the /proc/sys/kernel/default_relatime flag which can be changed runtime to modify the behavior of subsequent new mounts. tested by moving the date forward: # date Sun Aug 5 22:55:14 CEST 2007 # date -s "Tue Aug 7 22:55:14 CEST 2007" Tue Aug 7 22:55:14 CEST 2007 access to a file did not generate disk IO before the date was set, and it generated exactly one IO after the date was set. Signed-off-by: Ingo Molnar <mingo@elte.hu> --- Documentation/kernel-parameters.txt | 8 +++++ fs/Kconfig | 22 ++++++++++++++ fs/inode.c | 53 +++++++++++++++++++++++++++--------- fs/namespace.c | 24 ++++++++++++++++ include/linux/mount.h | 3 ++ kernel/sysctl.c | 17 +++++++++++ 6 files changed, 114 insertions(+), 13 deletions(-) Index: linux/Documentation/kernel-parameters.txt =================================================================== --- linux.orig/Documentation/kernel-parameters.txt +++ linux/Documentation/kernel-parameters.txt @@ -525,6 +525,10 @@ and is between 256 and 4096 characters. This is a 16-member array composed of values ranging from 0-255. + default_relatime= + [FS] mount all filesystems with relative atime + updates by default. + default_utf8= [VT] Format=<0|1> Set ...
On Mon, Aug 06, 2007 at 08:39:09AM +0200, Ingo Molnar wrote: > > * Dave Jones <davej@redhat.com> wrote: > > > > btw., Mutt does not go boom, i use it myself. It works just fine > > > and notices new mails even on a noatime,nodiratime filesystem. > > > > It still fails miserably for me. > > > > If I hit 'C' and '?' I get a list of my mail folders, with some of > > them marked 'N' if they have new mail. Without atime, those N's never > > show up and every mbox looks like it has no new mail. > > does it work with the "atime on steroids" patch below? (no need to > configure anything, just apply the patch and go.) people have reported that relatime does work, but my util-linux isn't new enough to support it, so I've never got it to work. I'll give your diff a try later, though as it seems to be equivalent I expect it'll work. Dave -- http://www.codemonkey.org.uk -
would still be nice if you could test it and report back :) Ingo -
you try to put the blame into distribution makers' shoes but in reality, had the kernel stepped forward with a neat .config option sooner (combined with a neat boot option as well to turn it off), we'd have had noatime systems 10 years ago. A new entry into relnotes and done. It's _much less_ of a compatibility impact than many of the changes that happen in a new distro release. (new glibc, new compiler, new kernel) Distro makers did not dare to do this sooner because some kernel developers came forward with these mostly bogus arguments ... The impact of atime is far better understood by the kernel community, so it is the responsibility of _us_ to signal such things towards distributors, not the other way around. Ingo -
Pretty much. AFAICS there was never a "policy decision" on the part of distro makers to begin with. The kernel had its default -- atime -- and the distros ran with that. Jeff -
Sorry Ingo, having been in the distribution business for over ten years I have to disagree. Kernel options that magically totally change the kernel You are trying to put a bogus divide between kernel community and developer community. Yet you know perfectly well that a large part of the kernel community yourself included work for distribution vendors and are actively building the distribution kernels. You are perfectly positioned to provide timing examples to the Fedora development team and make the case for FC8 beta going out that way. You are perfectly able to propose, build and submit a FC7 extras package of tuning which people can try in the meantime, but you haven't do so. Other people in this discussion can do likewise for Debian, SuSE etc. Your argument appears to be "I can't be bothered to use the due processes of the distribution but I can do it quickly with an ugly kernel hack". That is not the right approach. Propose it with your presented numbers to fedora-devel and I'll be happy to back up such a proposal for the next FC as will many other kernel folk I'm sure. Heck, go write a piece for LWN with the benchmark numbers and how to change your atime options. You'll make Jon happy and lots of folks read it and will give feedback on improvements as a result. Alan -
i've periodically pushed for a noatime distro kernel for like ... 5-10 years and last time this argument came up [i brought it up 6 months ago] most of the distro kernel developer actually recommended using noatime, but it took only 1-2 kernel developers to come out with the 'compatibility' and 'compliance' boogeyman to scare the distro userspace people away from changing /etc/fstab. so yes, things like this needs a clear message from the kernel folks, and a kernel option for that is a pretty good way of doing it. Ingo -
> it's default off of course. A distro can turn it on or off. And you honestly think that putting it in Kconfig as well as allowing users to screw up horribly and creating incompatible defaults you can't test for in a user space app where it matters is going to *change* this. Do you really think anyone who said "noatime, compatibility, umm errr" is going to say "noatime, compatibility, but hey its in Kconfig lets do it". You argument doesn't hold up to minimal rational consideration. Posting to the distribution devel list with: "Its a 50% performance win, we need to fix these corner cases, here's a tmpwatch patch" is *exactly* what is needed to change it, and Kconfig options are irrelevant to that. Be serious and do this the proper way, propose it for FC8, go through the proper due process. Otherwise the FC8 process will simply continue as "umm err, compatibility" and it'll go nowhere. You can't really complain about the CK scheduler and Con trying to do stuff his own way without listening and then do this can you ? Alan -
So far you've not offered one realistic scenario of "screw up horribly". People have been using noatime for a long time and there are no horror The patch i posted today adds /proc/sys/kernel/mount_with_atime. That i did exactly that 6 months ago, check your email folders. I went by the "process". But it doesnt really matter anymore, Ubuntu has done the step and Fedora will be forced to do it too. But it's sad that it took us 10 years. I'd like to remind you again: || ...For me, I would say 50% is not enough to describe the _visible_ || benefits... Not talking any specific number but past 10sec-1min+ || lagging in X is history, it's gone and I really don't miss it that || much... :-) Cannot reproduce even a second long delay anymore in || window focusing under considerable load as it's basically || instantaneous (I can see that it's loaded but doesn't affect the || feeling of responsiveness I'm now getting), even on some loads that I || couldn't previously even dream of... [...] we really have to ask ourselves whether the "process" is correct if advantages to the user of this order of magnitude can be brushed aside with simple "this breaks binary-only HSM" and "it's not standards compliant" arguments. Ingo -
On Sun, 5 Aug 2007 20:08:26 +0200 Whats this about "OSS". OSS or proprietary. And you've been given one example already - tmpwatch. Although its more of a trash compactor than And your Kconfig argument is still not rational. A question I note you chose not to answer. Anyway if Ubuntu has switched to noatime by default (or relatime) and hasn't used a Kconfig line that proves my whole point - Thats a discussion to have with your distribution development team. The kernel provides the required facilities already. Open source means everyone can do cool stuff as they see fit and natural selection will do the rest. Look I agree entirely with you that relatime, or noatime + minor package patches is the right thing to do for FC8. I've also pointed out you can build and release tuning packages for FC 7 and they'll make the distribution. FC8 beta 1 approaches so now is the time to be talking to the distribution people and to the ever kernel building Dave Jones about it. But none of this makes stupid Kconfig hacks the right answer. Alan -
Being standards compliant is not an argument it's a design goal, a requirement. Standards compliance is like pregant, you are or you're not. And to deliberately ignore standards for speed is saying "it's too hard to do it right, I'll do it wrong and it will be faster." The answer is to do it smarter, with solutions like relatime (which can be enhanced as Linus noted) which provide performance benefits without ignoring standards, or use of a filesystem which does a better job. But when it goes in the kernel the choice of having per-filesystem behavior either vanishes or becomes an exercise in complex and as-yet unwritten mount options. There are certainly ways to improve ext3, not journaling atime updates would certainly be one, less frequent updates of dirty inodes, whatever. But if a user wants to give up standards compliance it should be a deliberate choice, not something which the average user will not understand or learn to do. -- Bill Davidsen <davidsen@tmr.com> "We have more to fear from the bungling of the incompetent than from the machinations of the wicked." - from Slashdot -
Linux history says different. There was always the "final 1%" of compliance that required silliness we really did not want to bother with. Jeff -
This is not 1%, this is a user-visible change in behavior, relative to all previous Linux versions. There has been a way for ages to trade performance for standards for users or distributions, and standards have been chosen. Given that there is now a way to get virtually all of the performance without giving up atime completely, why the sudden attempt to change to a less satisfactory default? I could understand a push to quickly get relatime with a few enhancements (the functionality if not the exact code) into distributions, even as a default, but forcing user or distribution changes just to retain the same dehavior doesn't seem reasonable. It assumes that vendors and users are so stupid they can't understand why benchmark results and more important than standards. People who run servers are smart enough to decide if their application will run as expected without atime. People have lived with this compromise for a very long time, and it seems that a far more balanced solution will be in the kernel soon. -- bill davidsen <davidsen@tmr.com> CTO TMR Associates, Inc Doing interesting things with small computers since 1979 -
On Wed, 08 Aug 2007 15:39:52 -0400 This isn't about the 1% however. Its about API and ABI. Changing the default is a fairly evil ABI change. Telling everyone relatime is cool on desktops and defaulting it in the distro is not an ABI change and is very sensible -
Is there really enough benefit between relatime and noatime to justify that? If atime doesn't get updated at all it *will* impact operations, and unless there's a real performance gain the path which provides at least nominal POSIX compliance seems best. Plauger's law of least astonishment. -- Bill Davidsen <davidsen@tmr.com> "We have more to fear from the bungling of the incompetent than from the machinations of the wicked." - from Slashdot -
What numbers - I didn't quote any performance numbers ? -
ok, i misunderstood your "very few realise its more than a fraction of a percent" sentence, i thought you were saying it's a fraction of a percent. Measurements show that noatime helps 20-30% on regular desktop workloads, easily 50% for kernel builds and much more than that (in excess of 100%) for file-read-intense workloads. We cannot just walk past such a _huge_ performance impact so easily without even reacting to the performance arguments, and i'm happy Ubuntu picked up noatime,nodiratime and is whipping up the floor with Fedora on the desktop. just look at the spontaneous feedback this thread prompted: | ...For me, I would say 50% is not enough to describe the _visible_ | benefits... Not talking any specific number but past 10sec-1min+ | lagging in X is history, it's gone and I really don't miss it that | much... :-) Cannot reproduce even a second long delay anymore in | window focusing under considerable load as it's basically | instantaneous (I can see that it's loaded but doesn't affect the | feeling of responsiveness I'm now getting), even on some loads that I | couldn't previously even dream of... I still can get drawing lag a bit | by pushing enough stuff to swap but still it's definately quite well | under control, though rare 1-2 sec spikes in drawing appear due to | swap loads I think. ...And this is 2.6.21.5 so no fancies ala Ingo's | CFS or so yet... | | ...Thanks about this hint. :-) much of the hard performance work we put into the kernel and into userspace is basically masked by the atime stupidity. How many man-years did it take to implement prelink? It has less of an impact than noatime! How much effort did we put into smart readahead and bootup optimizations? It has less of an impact than noatime. Ingo -
And as everybody knows in servers is a popular practice to disable it. According to an interview to the kernel.org admins.... "Beyond that, Peter noted, "very little fancy is going on, and that is good because fancy is hard to maintain." He explained that the only fancy thing being done is that all filesystems are mounted noatime meaning that the system doesn't have to make writes to the filesystem for files which are simply being read, "that cut the load average in half." I bet that some people would consider such performance hit a bug... -
On Sun, 5 Aug 2007, Diego Calleja wrote: > El Sun, 5 Aug 2007 09:13:20 +0200, Ingo Molnar <mingo@elte.hu> escribi
yep - but note that this was a gradual effect along the years, today the assymetry between CPU performance and disk-seek performance is proportionally larger than 10 years ago. Today CPUs are nearly 100 times faster than 10 years ago, but disk seeks got only 2-3 times faster. (and even that only if you have a high rpm disk - most desktops dont.) 10 years ago noatime was a nifty hack that made a difference if you had lots of files. But it still was a problem with no immediate easy solution and people developed their counter-arguments. Today the same counter-arguments are used, but the situation has evolved alot. and note that often this has a bigger everyday effect than the tweaking of CPU scheduling, IO scheduling or swapping behavior (!). My desktop systems rarely swap, have plenty of CPU power to spare, but atime updates still have a noticeable latency impact, regardless of the memory pressure. Linux has _lots_ of "performance reserves", so people dont normally notice when comparing it to other OSs, but still we should not be so wasteful with our IO performance, for such a fundamental thing as reading files. Ingo -
To get that magnitude you need slow disk with very fast CPU. It helps most of systems where the disk hardware is marginal or worse for the i/o -- Bill Davidsen <davidsen@tmr.com> "We have more to fear from the bungling of the incompetent than from the machinations of the wicked." - from Slashdot -
I suspect that almost every single laptop with a Core2 Duo in it falls in= to that classification, and it's getting worse every year, as we see more disparity between CPU speeds (increasing) and disk seek times (basically = nailed to the floor for the last decade).
yeah - but i'd be surprised if more than 1% of all Linux servers out yeah. Ingo -
Sorry I'm just not seeing those gains here. With my filesystems mounted with atime defaults the Quake sources build in 1m28.856s. A test with ls -ltu verifies that atime is working as expected. When I remount my filesystems with: mount [fs] -o remount,noatime,nodiratime I get a compile time of 1m23.368s, a mere 6% improvement. This is on a dual-core Athlon 4200+ box running 2.6.21, so I would have thought this to be close to a best-case file I/O test. Greg -
what sort of disks does this box have? and what filesystem? slower disks/filesystems can result in this showing a larger difference. however 6% is a fairly significant gain. David Lang -
6% is nothing to sneeze at. A lot of optimizations would kill for less -Andi -
...For me, I would say 50% is not enough to describe the _visible_ benefits... Not talking any specific number but past 10sec-1min+ lagging in X is history, it's gone and I really don't miss it that much... :-) Cannot reproduce even a second long delay anymore in window focusing under considerable load as it's basically instantaneous (I can see that it's loaded but doesn't affect the feeling of responsiveness I'm now getting), even on some loads that I couldn't previously even dream of... I still can get drawing lag a bit by pushing enough stuff to swap but still it's definately quite well under control, though rare 1-2 sec spikes in drawing appear due to swap loads I think. ...And this is 2.6.21.5 so no fancies ala Ingo's CFS or so yet... ...Thanks about this hint. :-) -- i. -
Oh dear. Why not just make ext3 fsync() a no-op while you're at it? Distros can turn it back on if it's needed... Of course I'm not serious, but like atime, fsync() is something one expects to work if it's there. Disabling atime updates or making fsync() a no-op will both result in silent failure which I am sure we can agree is disasterous. Why on earth would you cripple the kernel defaults for ext3 (which is a fine FS for boot/root filesystems), when the *fundamental* problem you really want to solve lie much deeper in the implementation of the filesystem? Noatime doesn't solve the problem, it just makes it "less horrible". If you really need different filesystem performance characteristics, you can switch to another filesystem. There's plenty to choose from. -- / jakob -
No, they are nothing alike, and you are just making yourself look silly if you compare them. fsync has to do with fundamental guarantees about <rolls eyes> Climb down from hyperbole mountain. If you can show massive amounts of users that will actually be negatively impacted, please present hard evidence. atime updates -are- a fundamental problem, one you cannot solve by tweaking filesystem implementations. No matter how much you try to hide or batch, atime dirties an inode each time on every read... for a feature a tiny minority of programs care about, much less depend on. Remember several filesystems lock atime to mtime, because they do not have a concept of atime, and programs continue to work just fine. We already have field proof of how little atime matters in reality. Jeff -
On Sun, Aug 05, 2007 at 06:42:30AM -0400, Jeff Garzik wrote: Peace Jeff :) In another mail, I gave an example with tmpreaper clearing out unused files; if some of those files are only read and never modified, tmpreaper would start deleting files which were still frequently used. That's a regression, the way I see it. As for 'massive amounts of users', well, tmpreaper exists in most distros, so it's possible it has other users than just me. -- / jakob -
you mean tmpwatch? The trivial change below fixes this. And with that
we've come to the end of an extremely short list of atime dependencies.
Ingo
--- /etc/cron.daily/tmpwatch.orig
+++ /etc/cron.daily/tmpwatch
@@ -1,9 +1,9 @@
#! /bin/sh
-/usr/sbin/tmpwatch -x /tmp/.X11-unix -x /tmp/.XIM-unix -x /tmp/.font-unix \
+/usr/sbin/tmpwatch --mtime -x /tmp/.X11-unix -x /tmp/.XIM-unix -x /tmp/.font-unix \
-x /tmp/.ICE-unix -x /tmp/.Test-unix 10d /tmp
-/usr/sbin/tmpwatch 30d /var/tmp
+/usr/sbin/tmpwatch --mtime 30d /var/tmp
for d in /var/{cache/man,catman}/{cat?,X11R6/cat?,local/cat?}; do
if [ -d "$d" ]; then
- /usr/sbin/tmpwatch -f 30d "$d"
+ /usr/sbin/tmpwatch --mtime -f 30d "$d"
fi
done
-
Please read what I wrote, not what you think I wrote. If I only *read* those files, the mtime will not be updated, only the atime. And the files *will* then magically begin to disappear although they are frequently used. That will happen with a standard piece of software in a standard configuration, in a scenario that may or may not be common... I have no idea how common such a setup is - but I know how much it would suck to have files magically disappearing because of a kernel upgrade :) -- / jakob -
You wouldn't even need these kinds of games. What we could do is to make "relatime" updates a bit smarter. A bit smarter would be: - update atime if the old atime is <= than mtime/ctime Logic: things like mailers can care about whether some new state has been read or not. This is the current relatime. - update atime if the old atime is more than X seconds in the past (defaulting to one day or something) Logic: things like tmpwatch and backup software may want to remove stuff that hasn't been touched in a long time, but they sure don't care about "exact" atime. Now, you could also make the rule be that "X" depends on mtime/ctime, ie if a file has been "recently" created or modified, we keep more exact track of it and use one hour instead of one day, but if it's some old file that hasn't been modified in the last six months, we change X to a week. IOW, the "exactness" of atime is relative to how old the inode modifications are. We could obviously do with an additional rule: - update atime if the inode is dirty anyway. Logic: there's no downside. which just says that we'll make it exact if there is no reason not to. Linus -
ok, i've implemented this and it's working fine. Check out the relatime_need_update() function for the details of the logic. Atime update frequency is 1 day with that, and we update at least once after every modification as well, for the mailer logic. tested it by moving the date forward: # date Sun Aug 5 22:55:14 CEST 2007 # date -s "Tue Aug 7 22:55:14 CEST 2007" Tue Aug 7 22:55:14 CEST 2007 access to a file did not generate disk IO before the date was set, and it generated exactly one IO after the date was set. ( should i perhaps reduce the number of boot options and only use a single "norelatime_default" boot option to turn this off? ) Ingo ------------------------------------> Subject: [patch] add norelatime/relatime boot options, CONFIG_DEFAULT_RELATIME From: Ingo Molnar <mingo@elte.hu> change relatime updates to be performed once per day. This makes relatime a compatible solution for HSM, mailer-notification and tmpwatch applications too. also add the CONFIG_DEFAULT_RELATIME kernel option, which makes "norelatime" the default for all mounts without an extra kernel boot option. add the "norelatime" (and "relatime") boot options to enable/disable relatime updates for all filesystems. also add the /proc/sys/kernel/mount_with_relatime flag which can be changed runtime to modify the behavior of subsequent new mounts. tested by moving the date forward: # date Sun Aug 5 22:55:14 CEST 2007 # date -s "Tue Aug 7 22:55:14 CEST 2007" Tue Aug 7 22:55:14 CEST 2007 access to a file did not generate disk IO before the date was set, and it generated exactly one IO after the date was set. Signed-off-by: Ingo Molnar <mingo@elte.hu> --- Documentation/kernel-parameters.txt | 12 +++++++ fs/Kconfig | 17 ++++++++++ fs/inode.c | 48 ++++++++++++++++++++-------- fs/namespace.c | 61 ++++++++++++++++++++++++++++++++++++ include/linux/mount.h ...
ok, cleaned it up some more: only a single, consistent boot option and all the switches (be that config, boot or sysctl) are now called "default_relatime". Also, got rid of that #ifdef ugliness in namespace.c via a cleaner Kconfig solution (suggested by Peter Zijlstra). Ingo ----------------------------> Subject: [patch] implement smarter atime updates support From: Ingo Molnar <mingo@elte.hu> change relatime updates to be performed once per day. This makes relatime a compatible solution for HSM, mailer-notification and tmpwatch applications too. also add the CONFIG_DEFAULT_RELATIME kernel option, which makes "norelatime" the default for all mounts without an extra kernel boot option. add the "default_relatime=0" boot option to turn this off. also add the /proc/sys/kernel/default_relatime flag which can be changed runtime to modify the behavior of subsequent new mounts. tested by moving the date forward: # date Sun Aug 5 22:55:14 CEST 2007 # date -s "Tue Aug 7 22:55:14 CEST 2007" Tue Aug 7 22:55:14 CEST 2007 access to a file did not generate disk IO before the date was set, and it generated exactly one IO after the date was set. Signed-off-by: Ingo Molnar <mingo@elte.hu> --- Documentation/kernel-parameters.txt | 4 +++ fs/Kconfig | 22 ++++++++++++++++ fs/inode.c | 48 ++++++++++++++++++++++++++---------- fs/namespace.c | 25 ++++++++++++++++++ include/linux/mount.h | 2 + kernel/sysctl.c | 9 ++++++ 6 files changed, 97 insertions(+), 13 deletions(-) Index: linux/Documentation/kernel-parameters.txt =================================================================== --- linux.orig/Documentation/kernel-parameters.txt +++ linux/Documentation/kernel-parameters.txt @@ -525,6 +525,10 @@ and is between 256 and 4096 characters. This is a 16-member array composed of values ranging from 0-255. ...
new version: added the relatime_interval sysctl that allows the changing of the atime update frequency. (default: 1 day / 86400 seconds) Ingo --------------------------> Subject: [patch] [patch] implement smarter atime updates support From: Ingo Molnar <mingo@elte.hu> change relatime updates to be performed once per day. This makes relatime a compatible solution for HSM, mailer-notification and tmpwatch applications too. also add the CONFIG_DEFAULT_RELATIME kernel option, which makes "norelatime" the default for all mounts without an extra kernel boot option. add the "default_relatime=0" boot option to turn this off. also add the /proc/sys/kernel/default_relatime flag which can be changed runtime to modify the behavior of subsequent new mounts. tested by moving the date forward: # date Sun Aug 5 22:55:14 CEST 2007 # date -s "Tue Aug 7 22:55:14 CEST 2007" Tue Aug 7 22:55:14 CEST 2007 access to a file did not generate disk IO before the date was set, and it generated exactly one IO after the date was set. Signed-off-by: Ingo Molnar <mingo@elte.hu> --- Documentation/kernel-parameters.txt | 8 +++++ fs/Kconfig | 22 ++++++++++++++ fs/inode.c | 53 +++++++++++++++++++++++++++--------- fs/namespace.c | 24 ++++++++++++++++ include/linux/mount.h | 3 ++ kernel/sysctl.c | 17 +++++++++++ 6 files changed, 114 insertions(+), 13 deletions(-) Index: linux/Documentation/kernel-parameters.txt =================================================================== --- linux.orig/Documentation/kernel-parameters.txt +++ linux/Documentation/kernel-parameters.txt @@ -525,6 +525,10 @@ and is between 256 and 4096 characters. This is a 16-member array composed of values ranging from 0-255. + default_relatime= + [FS] mount all filesystems with relative atime + updates by default. + default_utf8= [VT] ...
What if you specify the interval as a per-mount option? i.e., mount -o relatime=86400 /dev/sda2 /u1 If you had this, I don't think we would need the sysctl tuning parameter. - Ted -
it's much more flexible if there are _more_ options available. People can thus make use of the feature earlier, use it even on distros that dont support it yet, etc. Ingo -
you might want to add /* * if the inode is dirty already, do the atime update since * we'll be doing the disk IO anyway to clean the inode. */ if (inode->i_state & I_DIRTY) return 1; -
This makes the actual result somewhat less predictable. Is that wise ? Right now its clear what happens based on what user sequence of events and that this is easily repeatable. -
I can see the repeatability argument; on the flipside, having a system of "opportunistic atime", eg as good as you can go cheaply, but with minimum guarantees has some attraction as well. For example one could imagine a system where the inode gets it's atime updated anyway, just not flagged for writing back to disk. If it later undergoes some event that would cause it to go to disk, it gets preserved... otoh that's even more unpredictable since VM pressure could drop this update early. For the dirty case, such drawbacks don't exist; it's just one more step of "when we can cheaply". -- if you want to mail me at work (you don't), use arjan (at) linux.intel.com Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org -
Changes behaviour so probably should default n. Better yet it should be All the above chunk is unneccessary as it can be a mount option. That avoids tons of messy extra code and complication. Users are far safer More code you don't need if you just leave it as a mount option. I'd much rather see the small clean patch for this as a mount option. Leave the rest to users/distros/lwn and it'll just happen now you've sorted the compabitility problems. -
no - it was not a double patch, i made all the common variants valid boot options: "relatime", "relatime=0/1", "norelatime" and "norelatime=0/1". Anyway, this is mooth, in the latest (v2) version relatime is a mount option already. And distros can disable it if they i fixed that in v2. Ingo -
Hi Jeff - just as a point to note, I think you should check the spec for fsync before stating that: "It is explicitly intended that a null implementation is permitted." and "... fsync() might or might not actually cause data to be written where it is safe from a power failure." http://www.opengroup.org/onlinepubs/009695399/functions/fsync.html So fsync() does not have to provide the fundamental guarantees you think it should. Note - I'm not saying that this is at all sane (it's crazy, IMO), I'm just pointing out that a "nofsync" mount option to avoid fsync overhead is a legal thing to do.... Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group -
I always thought the right solution would be to just sync atime only very very lazily. This means if a inode is only dirty because of an atime update put it on a "only write out when there is nothing to do or the memory is really needed" list. -Andi -
As I've mentioend earlier, the memory balancing issues that arise when we add an "atime dirty" bit scare me a little. It can be addressed, obviously, but at the cost of more code complexity. An alternative is to simply have a tunable parameter, via either a mount option or stashed in the superblock which controls atime's granularity guarantee. That is, only update the atime if it is older than some set time that could be configurable as a mount option or in the superblock. Most of the time, an HSM system simply wants to know if a file has been used sometime "recently", where recently might be measured in hours or in days. This is IMHO slightly better than relatime, since it keeps the spirit of the atime update, while keeping the performance impact to a very minimal (and tunable) level. - Ted P.S. Yet alternative is to specify noatime on an individual file/directory basis. We've had this capability for a *long* time, and if a distro were to set noatime for all files in certain hierarchies (i.e., /usr/include) and certain top-level directories (since the chattr +A flag is inherited), I think folks would find that this would reduce the I/O traffic of noatime by a huge amount. This also would be 100% POSIX compliant, since we are extending the filesystem and setting certain files to use it. But if users want to know when was the last time they looked at a particular file in their home directory, they would still have that facility. -
On Sun, 5 Aug 2007 11:00:29 -0400 ext3 and reiser both use a dirty_inode method to make sure that we don't actually have dirty inodes. This way, kswapd doesn't get stuck on the log and is able to do real work. It would be interesting to see a comparison of relatime with a kinoded that is willing to get stuck on the log. The FS would need a few tweaks so that write_inode() could know if it really needed to log or not, but for testing you could just drop ext3_dirty_inode and have ext3_write_inode do real work. Then just change kswapd to kick a new kinoded and benchmark away. A real patch would have to look for places where mark_inode_dirty was used and expected the dirty_inode callback to log things right away, but for testing its good enough. -chris -
On Sun, Aug 05, 2007 at 11:00:29AM -0400, Theodore Tso wrote: > P.S. Yet alternative is to specify noatime on an individual > file/directory basis. We've had this capability for a *long* time, > and if a distro were to set noatime for all files in certain > hierarchies (i.e., /usr/include) and certain top-level directories > (since the chattr +A flag is inherited) This came across my mind again earlier, and I went digging. Can you explain how this works? I've eyeballed the ext2/ext3 code, and feel like I'm missing something obvious. I'm guessing that for eg, with /usr/include/stdio.h, we check the inodes for all four parts of path, and if any of them are +A we avoid the atime update ? If so, where does that inheritance happen in the code? Dave -- http://www.codemonkey.org.uk -
Which is the policy I implemented for XFS a while ago. -
How would that work? I didn't think XFS had separate inode lists. -Andi -
Seems like a good idea. atimes will then be written only by memory pressure - or umount. The atimes could be wrong after a crash, but loosing atimes only is not something I'd worry about. Helge Hafting -
It has been years since I used MS Windows much, but from my memories of my these days, I was under the impression that it (at least the NT line, the only surviving line these days) also maintained "last accessed" times. Except I only ever saw it at "right now" because the file explorer ... accesses the file before getting this metadata or something like that (when you right-click on a file and ask for its properties). It has creation and last modification time, too. So, if my memories are correct, there is no performance edge to be conceded by having atime (but one to be gained by not having atime). -- Lionel -
NT maintains atimes by default, at least up to XP. You have to edit the registry to turn them off, and it is a single global switch -- not per mountpoint like Unix. And it makes a huge difference there, too. -
In windows Vista they've disabled atime updates by default. And XP maintains atimes, but it uses a trick to avoid the performance penalty we suffer in linux, similar to what Andi Kleen suggested: they keep atime updates in memory for one hour, and only sync to disk after that time - of course they also sync it if there's a oportunity to do it, like when updating mtime. -
Well it's not a problem with journalling per-se. Other journalling designs may well not have this problem. It's an unfortunate coupling: - the ext3 journal contains metadata from all altered files - ordered-mode needs to write back data for a file before committing its metdata to the journal. - fsync of one file requires a commit for its metadata, which will commit metadata for all files - hence we need to write back all data for all files which have metadata in the journal. It's pretty much unfixable given the ext3 journalling design, and the guarantees which data-ordered provides. The easy preventive is to mount with data=writeback. Maybe that should have been the default. -
Andrew Morton writes: [...] > > It's pretty much unfixable given the ext3 journalling design, and the > guarantees which data-ordered provides. ZFS has intent log to handle this (http://blogs.sun.com/realneel/entry/the_zfs_intent_log). Something like that can --theoretically-- be added to ext3-style journalling. Nikita. > > The easy preventive is to mount with data=writeback. Maybe that should > have been the default. -
The documentation I could find suggests that this may lead to a security weakness (old data in blocks of a file that was grown just before the crash leaks to a different user). XFS overwrites that data -
yup. This problem also exists in ext2, reiserfs (unless using If your computer is used by multiple users who don't trust each other, sure. That covers, what? About 2% of machines? I was using data=writeback for a while on my most-thrashed disk. The results were a bit disappointing - not much difference. ext2 is a lot quicker. (I don't use anything which is fsync-happy, btw). (I used to have a patch which sysctl-tunably turned fsync, msync, fdatasync into "return 0" for use on the laptop but I seem to have lost it) -
I wasn't concerned so much with security, but with user experience. For instance, some editors don't perform fsync-then-rename, but simply truncate the file when saving (because they want to preserve hard links). With XFS, this tends to cause null bytes on crashes. Since ext3 has got a much larger install base, this would result in lots of bug reports, I fear. Without zeroing, the truncating editor might garble the file in a more obvious way, but you've got the security issue (and I agree that this is more of a PR issue). -
XFS has recently been changed to only updated the on-disk i_size after data writeback has finished to get rid of this irritation. -
The other alternative which addresses the security concern is data=journal, which if you have a big enough journal, can sometimes be *faster* than data=ordered or even data=writeback, because it reduces seeking. The problem is that it's workload dependent which is better; if the workload is very, very heavy on data writes, each data block ends up getting writen twice, once to the journal and once to the final location on disk, and so this halves your total max write bandwidth. But if the workload doesn't do as much writing, and is very seeky, and or is very, very, fsync()-centric (like a mailhub), data=journal is probably the right answer. - Ted -
XFS has never overwritten data on reboot. It leaves holes when the kernel has failed to write out data. A hole == zeros so XFS does not expose stale data in this situation. As it is, the underlying XFS problem (lack of synchronisation between inode size update and data writes has been mostly fixed in 2.6.22 by only updating the file size to be written to disk on data I/O completion. FWIW, fsync() would prevent this from happening, but many application writers seem strangely reluctant to put fsync() calls into code to ensure the data they write is safely on disk..... Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group -
It should probably be doing fdatasync() instead. Then ext3 could just write the data blocks only, but only mess with the logs when the file size changed and mtime would be written out somewhat later. [unless you have data logging enabled] Does the problem go away when you change it to that? -Andi -
Well, quite frankly, there are other changes between 2.6.18 and 2.6.21 that are more likely to be a big deal than Peter's patches. No offense to Peter, but we also cut the default dirty percentage by a factor of four in that timeframe, and that made a *huge* difference for some setups (and Hey, I'm not complaining. I think the code looks fine. I just want to make So do the patches really end up helping your case? Or is this just why you're following it, and hoping they'll eventually do so? Linus -
> Per device dirty throttling patches This one interests me most, due to various real life, reported problems with fuse filesystems. For this reason I'd really like to get this or a subset of it into mainline as soon as possible. This patchset (or rather the -v7 version) has been running on my laptop for a couple of weeks without problems. I've also verified that it solves the fuse and loop issues. I have some qualms about the complexity of various parts though. Especially the "proportions" library, which I'm having problems understanding. I'm not sure that this level of sophistication is really needed to solve the issues with the old code. Miklos -
<snip> Hi Peter, I've been testing your patch with a simple test case that copies a 3GB file from sda -> sda, and copies a 1GB file from sda -> sdb. the script is roughly this :- dd bs=64k if=[sda]/data3g of=[sda]/temp_data3g & sleep 60 dd bs=64k if=[sda]/data1g of=[sdb]/temp_data1g & wait sleep 200 On my amd64x2 desktop machine where sda is a sata 250 GB drive & sdb is an ide 300 GB drive. Running this test 5 times gives 2.6.23-rc1-mm2 1GB copy MB/s 3GB copy MB/s 16.2 16.1 15.2 14.6 17.3 14.6 18.0 14.5 19.0 14.6 2.6.23-rc1-mm2+pddt_patch 1GB copy MB/s 3GB copy MB/s 23.0 14.7 24.0 14.6 20.4 14.8 22.6 14.5 23.2 14.5 This is on a standard desktop machine so there are lots of other processes running on it, and although there is a degree of variability in the numbers,they are very repeatable and your patch always out performs the stock mm2. looks good to me Richard -
iirc the goal of this is less to get better performance, but to avoid long user visible latencies. Of course if it's faster it's great too, but that's only secondary. -Andi -
What a trade-off, if you want to get rid of long latency you have to live with better throughput. I can live with that. ;-) Your point well taken, not the intent of the patch, but it may indicate where a performance bottleneck happens as well. -- Bill Davidsen <davidsen@tmr.com> "We have more to fear from the bungling of the incompetent than from the machinations of the wicked." - from Slashdot -
| Greg KH | Og dreams of kernels |
| Jens Axboe | [PATCH 31/33] Fusion: sg chaining support |
| Arnd Bergmann | Re: finding your own dead "CONFIG_" variables |
| Mark Brown | [PATCH 2/2] Subject: natsemi: Allow users to disable workaround for DspCfg reset |
| Tony Breeds | [LGUEST] Look in object dir for .config |
git: | |
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| John Benes | Re: master has some toys |
| Matthias Lederhofer | [PATCH 4/7] introduce GIT_WORK_TREE to specify the work tree |
| Alexander Sulfrian | [RFC/PATCH] RE: git calls SSH_ASKPASS even if DISPLAY is not set |
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