From: Peter Staubach <staubach@redhat.com>
Subject: Re: Re: [PATCH] Smooth out NFS client writeback
Date: Wed, 29 Jun 2005 10:11:24 -0400
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Cc: Trond Myklebust <trond.myklebust@fys.uio.no>,
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To: Shantanu Goel <sgoel01@yahoo.com>
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Shantanu Goel wrote:

>Hi Trond,
>
>Attached is the long delayed revised version of the
>writeback smoothing patch this time against
>2.6.12-mm2.  I have omitted the commit w/range and
>mmap writeback from this one.  If this one is deemed
>acceptable for inclusion I'll post the other 2 later. 
>The commit w/range really should be restored as it
>makes quite a difference against Solaris NFS servers
>with regular disks.  I observed a difference of 2-3
>MB/s under sustained writes.  It makes no difference
>with the Linux NFS server since it ignores the range.
>

On Solaris, at least with UFS as the underlying file system, the COMMIT
operations are processed by looking through the entire cached page list
or by doing page lookup operations on each individual page.  If the entire
file is specified, ie. len = 0, then the page list is walked.  If a range
is specified, then just the pages within the range are looked up.

Specifying the range can result in significantly less CPU overhead on the
server.  This is why the NFSv3 COMMIT operation has a range which can be
specified...  :-)

       ps


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