Messages in this thread Patch in this message | | | Subject | [PATCH] [3.7-rc] fix incorrect NR_FREE_PAGES accounting (appears like memory leak) | From | Dave Hansen <> | Date | Wed, 21 Nov 2012 14:21:51 -0500 |
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This needs to make it in before 3.7 is released.
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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 <dave@linux.vnet.ibm.com> Acked-by: Mel Gorman <mgorman@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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