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authorSonny Rao <sonnyrao@chromium.org>2012-12-20 15:05:07 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-01-11 09:06:48 -0800
commit711cf004f2148f1d1967bc5eca025019e5001212 (patch)
tree83ba439251b29610cc5ea1f6626d0190521769d9 /mm
parent6cb6a94380506d9e5491b8e145811bd676ce6f3d (diff)
downloadlinux-linaro-stable-711cf004f2148f1d1967bc5eca025019e5001212.tar.gz
mm: fix calculation of dirtyable memory
commit c8b74c2f6604923de91f8aa6539f8bb934736754 upstream. 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> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/page-writeback.c25
1 files changed, 20 insertions, 5 deletions
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 26adea8ca2e7..bc8465f579a8 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -187,6 +187,18 @@ static unsigned long highmem_dirtyable_memory(unsigned long total)
zone_reclaimable_pages(z) - z->dirty_balance_reserve;
}
/*
+ * Unreclaimable memory (kernel memory or anonymous memory
+ * without swap) can bring down the dirtyable pages below
+ * the zone's dirty balance reserve and the above calculation
+ * will underflow. However we still want to add in nodes
+ * which are below threshold (negative values) to get a more
+ * accurate calculation but make sure that the total never
+ * underflows.
+ */
+ if ((long)x < 0)
+ x = 0;
+
+ /*
* Make sure that the number of highmem pages is never larger
* than the number of the total dirtyable memory. This can only
* occur in very strange VM situations but we want to make sure
@@ -208,8 +220,8 @@ unsigned long global_dirtyable_memory(void)
{
unsigned long x;
- x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages() -
- dirty_balance_reserve;
+ x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages();
+ x -= min(x, dirty_balance_reserve);
if (!vm_highmem_is_dirtyable)
x -= highmem_dirtyable_memory(x);
@@ -276,9 +288,12 @@ static unsigned long zone_dirtyable_memory(struct zone *zone)
* highmem zone can hold its share of dirty pages, so we don't
* care about vm_highmem_is_dirtyable here.
*/
- return zone_page_state(zone, NR_FREE_PAGES) +
- zone_reclaimable_pages(zone) -
- zone->dirty_balance_reserve;
+ unsigned long nr_pages = zone_page_state(zone, NR_FREE_PAGES) +
+ zone_reclaimable_pages(zone);
+
+ /* don't allow this to underflow */
+ nr_pages -= min(nr_pages, zone->dirty_balance_reserve);
+ return nr_pages;
}
/**