linux-kernel - Re: [PATCH] knfsd: Stop NFSD writes from being broken into lots of little writes to filesystem.

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Message-Id: <20070214134408.431cddcc.akpm@linux-foundation.org>
Date:	Wed, 14 Feb 2007 13:44:08 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	NeilBrown <neilb@...e.de>, nfs@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org,
	Norman Weathers <norman.r.weathers@...ocophillips.com>,
	"Vladimir V \".\" Saveliev" <vs@...esys.com>
Subject: Re: [PATCH] knfsd: Stop NFSD writes from being broken into lots of
 little writes to filesystem.

On Tue, 13 Feb 2007 17:11:19 +1100
Nick Piggin <nickpiggin@...oo.com.au> wrote:

> NeilBrown wrote:
> > Another nfsd patch for 2.6.21...
> > 
> > ### Comments for Changeset
> > 
> > When NFSD receives a write request, the data is typically in a number
> > of 1448 byte segments and writev is used to collect them together.
> > 
> > Unfortunately, generic_file_buffered_write passes these to the filesystem
> > one at a time, so an e.g. 32K over-write becomes a series of partial-page
> > writes to each page, causing the filesystem to have to pre-read those
> > pages - wasted effort.
> > 
> > generic_file_buffered_write handles one segment of the vector at a
> > time as it has to pre-fault in each segment to avoid deadlocks.  When
> > writing from kernel-space (and nfsd does) this is not an issue, so
> > generic_file_buffered_write does not need to break and iovec from nfsd
> > into little pieces.
> > 
> > This patch avoids the splitting when  get_fs is KERNEL_DS as it is
> > from NFSd.
> > 
> > This issue was introduced by commit 6527c2bdf1f833cc18e8f42bd97973d583e4aa83
> > 
> > Cc: Nick Piggin <nickpiggin@...oo.com.au>
> 
> FWIW, you can put Acked-by: me there if you'd like.
> 

It's yet another patch we need to revert if/when we get the write()-deadlock
stuff sorted out.  So please add negative-this to that patch series.
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