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. Change-Id: Ib0c4a8f99870edc5ded863b88a472f2836c690d2 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> Git-commit: c8b74c2f6604923de91f8aa6539f8bb934736754 Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git Signed-off-by: Laura Abbott <lauraa@codeaurora.org>

Signed-off-by: evolutionmod <kernelcraft@gmail.com>