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| author | Sonny Rao <sonnyrao@chromium.org> | 2012-12-20 15:05:07 -0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2013-01-11 09:06:48 -0800 |
| commit | 711cf004f2148f1d1967bc5eca025019e5001212 (patch) | |
| tree | 83ba439251b29610cc5ea1f6626d0190521769d9 /mm/page-writeback.c | |
| parent | 6cb6a94380506d9e5491b8e145811bd676ce6f3d (diff) | |
| download | lwn-711cf004f2148f1d1967bc5eca025019e5001212.tar.gz lwn-711cf004f2148f1d1967bc5eca025019e5001212.zip | |
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/page-writeback.c')
| -rw-r--r-- | mm/page-writeback.c | 25 |
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; } /** |