[PATCH 3.12 172/206] mm: free compound page with correct order

From: Jiri Slaby
Date: Tue Nov 18 2014 - 09:20:44 EST

From: Yu Zhao <yuzhao@xxxxxxxxxx>

3.12-stable review patch. If anyone has any objections, please let me know.


commit 5ddacbe92b806cd5b4f8f154e8e46ac267fff55c upstream.

Compound page should be freed by put_page() or free_pages() with correct
order. Not doing so will cause tail pages leaked.

The compound order can be obtained by compound_order() or use
HPAGE_PMD_ORDER in our case. Some people would argue the latter is
faster but I prefer the former which is more general.

This bug was observed not just on our servers (the worst case we saw is
11G leaked on a 48G machine) but also on our workstations running Ubuntu
based distro.

$ cat /proc/vmstat | grep thp_zero_page_alloc
thp_zero_page_alloc 55
thp_zero_page_alloc_failed 0

This means there is (thp_zero_page_alloc - 1) * (2M - 4K) memory leaked.

Fixes: 97ae17497e99 ("thp: implement refcounting for huge zero page")
Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Mel Gorman <mel@xxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Bob Liu <lliubbo@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
mm/huge_memory.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 10532dd43abc..e497843f5f65 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -192,7 +192,7 @@ retry:
if (cmpxchg(&huge_zero_page, NULL, zero_page)) {
- __free_page(zero_page);
+ __free_pages(zero_page, compound_order(zero_page));
goto retry;

@@ -224,7 +224,7 @@ static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
struct page *zero_page = xchg(&huge_zero_page, NULL);
BUG_ON(zero_page == NULL);
- __free_page(zero_page);
+ __free_pages(zero_page, compound_order(zero_page));
return HPAGE_PMD_NR;


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