linux-kernel - Re: patch: improve generic_file_buffered

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Message-Id: <200709080612.52749.nickpiggin@yahoo.com.au>
Date:	Sat, 8 Sep 2007 06:12:52 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Goswin von Brederlow <brederlo@...ormatik.uni-tuebingen.de>
Cc:	Bernd Schubert <bs@...eap.de>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	linux-kernel@...r.kernel.org,
	"J. Bruce Fields" <bfields@...ldses.org>, brian@...sterfs.com
Subject: Re: patch: improve generic_file_buffered_write() (2nd try 1/2)

On Saturday 08 September 2007 19:43, Goswin von Brederlow wrote:
> Nick Piggin <nickpiggin@...oo.com.au> writes:
> > Lustre should probably have to be ported over to write_begin/write_end in
> > order to use it too. With the patches in -mm, if a filesystem is still
> > using prepare_write/commit_write, the vm reverts to a safe path which
> > avoids the deadlock (and allows multi-seg io copies), but copies the data
> > twice.
>
> Not quite relevant for the performance problem. The situation is like
> this:
>
> lustre servers  <-lustre network protocol-> lustre client <-NFS-> desktop
>
> The NFSd problem is on the lustre client that only plays gateway. That
> is not to say that the lustre servers or desktop loose performance due
> to fragmenting writes too but it isn't that noticeable there.

OK, but the filesystem client would need to support write_begin/write_end
in order for writes to do multi-seg iovecs. nfsd of course will also be fixed
by the earlier patch I referenced, but you did want userspace multi-seg
writes to work too...


> > OTOH, this is very likely to go upstream, so your filesystem will need to
> > be ported over sooner or later anyway.
>
> Lustre copies the ext3 source from the kernel, patches in some extra
> features and renames them during build. So one the one hand it always
> breaks whenever someone meddles with the ext3 code. On the other hand
> improvement for ext3 get picked up by lustre semi automatically.
>
> In this case lustre would get the begin_write() function from ext3 and
> use it.

OK. Yes ext3 is converted in -mm.
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