linux-kernel - Re: [PATCH] fadvise: only initiate writeback for specified range with FADV

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Date:	Tue, 1 Nov 2011 16:05:55 +0100
From:	Johannes Weiner <jweiner@...hat.com>
To:	Shawn Bohrer <sbohrer@...advisors.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fadvise: only initiate writeback for specified range
 with FADV_DONTNEED

On Mon, Oct 31, 2011 at 11:16:59AM -0500, Shawn Bohrer wrote:
> Previously POSIX_FADV_DONTNEED would start writeback for the entire file
> when the bdi was not write congested.  This negatively impacts
> performance if the file contians dirty pages outside of the requested
> range.  This change uses __filemap_fdatawrite_range() to only initiate
> writeback for the requested range.
> 
> Signed-off-by: Shawn Bohrer <sbohrer@...advisors.com>

It probably makes sense for some cases to take advantage of the disk
head being nearby and flush more than requested.

But I can certainly see this go wrong by taking away the write-caching
benefits for the rest of the file just because a small part of it was
fadvised.

Acked-by: Johannes Weiner <jweiner@...hat.com>
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