[PATCH 1/4] slab: do ClearSlabPfmemalloc() for all pages of slab

From: Mel Gorman
Date: Tue Sep 04 2012 - 13:24:57 EST


Right now, we call ClearSlabPfmemalloc() for first page of slab when we
clear SlabPfmemalloc flag. This is fine for most swap-over-network use
cases as it is expected that order-0 pages are in use. Unfortunately it
is possible that that __ac_put_obj() checks SlabPfmemalloc on a tail page
and while this is harmless, it is sloppy. This patch ensures that the head
page is always used.

This problem was originally identified by Joonsoo Kim.

[js1304@xxxxxxxxx: Original implementation and problem identification]
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
---
mm/slab.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index 811af03..d34a903 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1000,7 +1000,7 @@ static void *__ac_get_obj(struct kmem_cache *cachep, struct array_cache *ac,
l3 = cachep->nodelists[numa_mem_id()];
if (!list_empty(&l3->slabs_free) && force_refill) {
struct slab *slabp = virt_to_slab(objp);
- ClearPageSlabPfmemalloc(virt_to_page(slabp->s_mem));
+ ClearPageSlabPfmemalloc(virt_to_head_page(slabp->s_mem));
clear_obj_pfmemalloc(&objp);
recheck_pfmemalloc_active(cachep, ac);
return objp;
@@ -1032,7 +1032,7 @@ static void *__ac_put_obj(struct kmem_cache *cachep, struct array_cache *ac,
{
if (unlikely(pfmemalloc_active)) {
/* Some pfmemalloc slabs exist, check if this is one */
- struct page *page = virt_to_page(objp);
+ struct page *page = virt_to_head_page(objp);
if (PageSlabPfmemalloc(page))
set_obj_pfmemalloc(&objp);
}
--
1.7.9.2

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