Hi ,
 just to give some feedback on 2.6.24-rc1. For some time I am tracking IO/writeback problems that hurt system responsiveness big-time. I tested Peters stuff together with Fenguangs additions and it looked promising. Therefore I was very happy to see Peters stuff going into 2.6.24 and waited eagerly for rc1. In short, I am impressed. This really looks good. IO throughput is great and I could not reproduce the responsiveness problems so far.
 Below are a some numbers of my brute-force I/O tests that I can use to bring responsiveness down. My platform is a HP/DL380g4, dual CPUs, HT-enabled, 8 GB Memory, SmartaArray6i controller with 4x72GB SCSI disks as RAID5 (battery protected writeback cahe enabled) and gigabit networking (tg3). User space is 64-bit RHEL4.3
 I am basically doing copies using "dd" with 1MB blocksize. Local Filesystem ist ext2 (noatime). IO-Scheduler is dealine, as it tends to give best results. NFS3 Server is a Sun/T2000/Solaris10. The tests are:
dd1 - copy 16 GB from /dev/zero to local FS

dd1-dir - same, but using O_DIRECT for output

dd2/dd2-dir - copy 2x7.6 GB in parallel from /dev/zero to local FS

dd3/dd3-dir - copy 3x5.2 GB in parallel from /dev/zero lo local FS

net1 - copy 5.2 GB from NFS3 share to local FS

mix3 - copy 3x5.2 GB from /dev/zero to local disk and two NFS3 shares
 I did the numbers for 2.6.19.2, 2.6.22.6 and 2.6.24-rc1. All units are MB/sec.
test           2.6.19.2     2.6.22.6    2.6.24.-rc1

----------------------------------------------------------------

dd1           28            50                96

dd1-dir     88                88                86

dd2          2x16.5       2x11            2x44.5

dd2-dir      2x44          2x44            2x43

dd3            3x9.8        3x8.7         3x30

dd3-dir      3x29.5      3x29.5        3x28.5

net1            30-33         50-55         37-52

mix3           17/32         25/50        96/35 (disk/combined-network)
 Some observations:
- single threaded disk speed really went up wit 2.6.24-rc...
[ message continues ]

wow, really nice results! Peter does know how to make stuff fast :) Now 
Such as the rewritten reclaim (clockpro) patches:
  http://programming.kicks-ass.net/kernel-patches/page-replace/
The improve-swap-performance (swap-token) patches:
  http://programming.kicks-ass.net/kernel-patches/swap_token/
His enable-swap-over-NFS [and other complex IO transports] patches:
  http://programming.kicks-ass.net/kernel-patches/vm_deadlock/
And the concurrent pagecache patches:
  http://programming.kicks-ass.net/kernel-patches/concurrent-pagecache/
as a starter :-) I think the MM should get out of deep-feature-freeze

mode - there's tons of room to improve :-/
	Ingo "runs and hides" Molnar

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On Fri, 26 Oct 2007 17:22:21 +0200
Those changes seem suspiciously large to me.  I wonder if there's less

physical IO happening during the timed run, and correspondingly more
Kidding.  We merge about 265 MM patches in 2.6.24-rc1:
 482 files changed, 8071 insertions(+), 5142 deletions(-)
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On Fri, 26 Oct 2007 12:21:55 -0700
another option... this is ext2.. didn't the ext2 reservation stuff get

merged into -rc1? for ext3 that gave a 4x or so speed boost (much

better sequential allocation pattern)
(or maybe I'm just wrong)

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Yes, one would expect that to make a large difference in dd2/dd2-dir and

dd3/dd3-dir - but only on SMP.  On UP there's not enough concurrency in the

fs block allocator for any damage to occur.
Reservations won't affect dd1 though, and that went faster too.

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so a final 'sync' should be added to the test too, and the time it takes 
impressive :)
	Ingo

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On Fri, 26 Oct 2007 21:33:40 +0200
That's one way of doing it.  Or just run the test for a "long" time.  ie:

much longer than (total-memory / disk-bandwidth).  Probably the latter
A lot of that was new functionality.  That's easier to add than things

which change long-standing functionality.

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Longer might be less inaccurate, but without flushing the last data you

really don't get best accuracy, you just reduce the error. Clearly doing

fdatasync() is best, since other i/o caused by sync() can skew the results.
--

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
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I think riel is taking over that stuff with his split vm and policies
Will post that one again, soonish.... Esp. after Linus professed liking

to have swap over NFS.
I've been working on improving the changelogs and comments in that code.
latest code (somewhat raw, as rushed by ingo posting this) in:
Yeah, that one would be cool, but it depends on Nick getting his

lockless pagecache upstream. For those who don't know, both are in -rt

(and have been for some time) so it's not unproven code.

On Fri, 26 Oct 2007 17:29:00 +0200
I am.  Taking every single reference to a page into account simply

won't scale to systems with 1TB of RAM.  This is why I am working

on implementing:
http://linux-mm.org/PageReplacementDesign
At the moment I only have the basic "plumbing" of the split VM

working and am fixing some bugs in that.  Expect a patch series

with that soon, so you guys can review that code and tell me

where to beat it into shape some more :)
After that I will work on the policy bits, where we can really

get performance benefits.  The patch series should be mergeable

in smaller increments, so we can take things slowly if desired.
--

"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

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