commit 441c228f817f7597e090d84aca74bdb7c2bd5040
author Mel Gorman <mgorman@suse.de> Fri Dec 12 16:56:33 2014 -0800
committer Linus Torvalds <torvalds@linux-foundation.org> Sat Dec 13 12:42:49 2014 -0800
tree 2b03cb17475aeb302d230e4c36dcd18a374a05f6
parent 7e5b528b4ce31208ef5c240c14beec4853d8262c

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>