From: Mel Gorman <mgorman@suse.de>
Date: Sat, 13 Dec 2014 00:56:33 +0000 (-0800)
Subject: mm: fadvise: document the fadvise(FADV_DONTNEED) behaviour for partial pages
X-Git-Tag: omap-for-v3.19/fixes-rc1~100^2~49
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=441c228f817f7597e090d84aca74bdb7c2bd5040;p=pandora-kernel.git

mm: fadvise: document the fadvise(FADV_DONTNEED) behaviour for partial pages

A random seek IO benchmark appeared to regress because of a change to
readahead but the real problem was the benchmark.  To ensure the IO
request accesssed disk, it used fadvise(FADV_DONTNEED) on a block boundary
(512K) but the hint is ignored by the kernel.  This is correct but not
necessarily obvious behaviour.  As much as I dislike comment patches, the
explanation for this behaviour predates current git history.  Clarify why
it behaves like this in case someone "fixes" fadvise or readahead for the
wrong reasons.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

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