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

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Date:	Tue, 13 Feb 2007 17:11:19 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	NeilBrown <neilb@...e.de>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	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.

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.

Thanks,
Nick

-- 
SUSE Labs, Novell Inc.
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