Re: [2/3] POHMELFS: Documentation.

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To: Jamie Lokier <jamie@...>
Cc: <linux-kernel@...>, <netdev@...>, <linux-fsdevel@...>
Date: Saturday, June 14, 2008 - 2:56 am

On Sat, Jun 14, 2008 at 03:15:47AM +0100, Jamie Lokier (jamie@shareable.org) wrote:

Noreover, that's true :)
I regulary run and post various benchmarks comparing POHMELFS, NFS,
XFS and Ext4, main goal of POHMELFS at this stage is to be
essentially as fast as underlying local filesystem. And it is...
Though there is a single place (random reading, all others reached
FS speed, so it is from 10 to 300% faster than NFS in various loads :),
but I'm working on it, I think it is not server's side though.


Maybe it was a bit naive though :)
But I checked lots of implementation, all of them use send()/recv()
approach. NFSv4 uses a bit different, but it is a cryptic, and at least
from its names it is not clear:
like nfs_pagein_multi() -> nfs_pageio_complete() -> add_stats. Presumably
we add stats when we have data handy...
CIFS/SMB use synchronous approach.

From those projects, which are not in kernel, like CRFS and CEPH, the
former uses async receiving thread, while the latter is synchronous,
but can select different servers for reading, more like NFSv4.1 leases.


It covers all operations, including reading, directory listing, lookups,
attribite changes and so on. Its main goal is to allow transaparent
failover, so it has to be done for reading too.


Oplocks and leases are essentially lock on given file, which allows one
client to operate on it. POHMELFS does not have locks now, and they will
be created depending on how distributed server will require them. In the
simplesst case it can just lock file for writing and do not allow its
updates from other clients. Lock aciquite can be done at write_begin
time. Without lock and writeback cache in your case writeback for file Y
can happen before writeback for file X, but if client does not only
write, but also sync after its write, then yes, client will see later
updates after more earlier. POHMELFS does not broadcast its interest in
the file content until real writing happens, i.e. at writeback time.
Although I can add a mode, when the same will be done during
write_begin() time. In that case your example will work without sync.


-- 
	Evgeniy Polyakov
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Messages in current thread:
[0/3] POHMELFS high performance network filesystem. First st..., Evgeniy Polyakov, (Fri Jun 13, 12:37 pm)
[3/3] POHMELFS high performance network filesystem., Evgeniy Polyakov, (Fri Jun 13, 12:42 pm)
Re: [3/3] POHMELFS high performance network filesystem., Vegard Nossum, (Sun Jun 15, 3:47 am)
Re: [3/3] POHMELFS high performance network filesystem., Evgeniy Polyakov, (Sun Jun 15, 5:14 am)
[2/3] POHMELFS: Documentation., Evgeniy Polyakov, (Fri Jun 13, 12:41 pm)
Re: [2/3] POHMELFS: Documentation., Jamie Lokier, (Fri Jun 13, 10:15 pm)
Re: [2/3] POHMELFS: Documentation., Evgeniy Polyakov, (Sat Jun 14, 2:56 am)
Re: [2/3] POHMELFS: Documentation., Sage Weil, (Sun Jun 15, 12:27 am)
Re: [2/3] POHMELFS: Documentation., Evgeniy Polyakov, (Sun Jun 15, 1:57 am)
Re: [2/3] POHMELFS: Documentation., Sage Weil, (Sun Jun 15, 12:41 pm)
Re: [2/3] POHMELFS: Documentation., Evgeniy Polyakov, (Sun Jun 15, 1:50 pm)
Re: [2/3] POHMELFS: Documentation., Sage Weil, (Sun Jun 15, 11:17 pm)
Re: [2/3] POHMELFS: Documentation., Evgeniy Polyakov, (Mon Jun 16, 6:20 am)
Re: [2/3] POHMELFS: Documentation., Trond Myklebust, (Sat Jun 14, 2:45 pm)
Re: [2/3] POHMELFS: Documentation., Evgeniy Polyakov, (Sat Jun 14, 3:25 pm)
Re: [2/3] POHMELFS: Documentation., Jeff Garzik, (Sat Jun 14, 5:49 am)
[1/3] POHMELFS: VFS trivial change., Evgeniy Polyakov, (Fri Jun 13, 12:40 pm)