This needs to make it in before 3.7 is released.
--
There have been some 3.7-rc reports of vm issues, including some
kswapd bugs and, more importantly, some memory "leaks":
http://www.spinics.net/lists/linux-mm/msg46187.html
https://bugzilla.kernel.org/show_bug.cgi?id=50181
The post-3.6 commit 1fb3f8ca took split_free_page() and reused
it for the compaction code. It does something curious with
capture_free_page() (previously known as split_free_page()):
int capture_free_page(struct page *page, int alloc_order,
...
__mod_zone_page_state(zone, NR_FREE_PAGES, -(1UL << order));
- /* Split into individual pages */
- set_page_refcounted(page);
- split_page(page, order);
+ if (alloc_order != order)
+ expand(zone, page, alloc_order, order,
+ &zone->free_area[order], migratetype);
Note that expand() puts the pages _back_ in the allocator, but it
does not bump NR_FREE_PAGES. We "return" 'alloc_order' worth of
pages, but we accounted for removing 'order' in the
__mod_zone_page_state() call. For the old split_page()-style use
(order==alloc_order) the bug will not trigger. But, when called
from the compaction code where we occasionally get a larger page
out of the buddy allocator than we need, we will run in to this.
This patch simply changes the NR_FREE_PAGES manipulation to the
correct 'alloc_order' instead of 'order'.
I've been able to repeatedly trigger this in my testing
environment. The amount "leaked" very closely tracks the
imbalance I see in buddy pages vs. NR_FREE_PAGES. I have
confirmed that this patch fixes the imbalance
Signed-off-by: Dave Hansen <d...@linux.vnet.ibm.com>
Acked-by: Mel Gorman <mgor...@suse.de>
---
linux-2.6.git-dave/mm/page_alloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN mm/page_alloc.c~leak-fix-20121120-2 mm/page_alloc.c
--- linux-2.6.git/mm/page_alloc.c~leak-fix-20121120-2 2012-11-21
14:14:52.053714749 -0500
+++ linux-2.6.git-dave/mm/page_alloc.c 2012-11-21 14:14:52.069714883 -0500
@@ -1405,7 +1405,7 @@ int capture_free_page(struct page *page,
mt = get_pageblock_migratetype(page);
if (unlikely(mt != MIGRATE_ISOLATE))
- __mod_zone_freepage_state(zone, -(1UL << order), mt);
+ __mod_zone_freepage_state(zone, -(1UL << alloc_order), mt);
if (alloc_order != order)
expand(zone, page, alloc_order, order,
_
--
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