From: Sonny Rao <sonnyrao@chromium.org>
Date: Thu, 20 Dec 2012 23:05:07 +0000 (-0800)
Subject: mm: fix calculation of dirtyable memory
X-Git-Tag: v3.8-rc1~12^2~23
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c8b74c2f6604923de91f8aa6539f8bb934736754;p=pandora-kernel.git

mm: fix calculation of dirtyable memory

The system uses global_dirtyable_memory() to calculate number of
dirtyable pages/pages that can be allocated to the page cache.  A bug
causes an underflow thus making the page count look like a big unsigned
number.  This in turn confuses the dirty writeback throttling to
aggressively write back pages as they become dirty (usually 1 page at a
time).  This generally only affects systems with highmem because the
underflowed count gets subtracted from the global count of dirtyable
memory.

The problem was introduced with v3.2-4896-gab8fabd

Fix is to ensure we don't get an underflowed total of either highmem or
global dirtyable memory.

Signed-off-by: Sonny Rao <sonnyrao@chromium.org>
Signed-off-by: Puneet Kumar <puneetster@chromium.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Tested-by: Damien Wyart <damien.wyart@free.fr>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

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