[PATCH 03/97] slab: correct pfmemalloc check

From: Mel Gorman
Date: Thu Aug 28 2014 - 15:09:54 EST

From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>

commit 73293c2f900d0adbb6a415b312cd57976d5ae242 upstream.

We checked pfmemalloc by slab unit, not page unit. You can see this
in is_slab_pfmemalloc(). So other pages don't need to be set/cleared

And, therefore we should check pfmemalloc in page flag of first page,
but current implementation don't do that. virt_to_head_page(obj) just
return 'struct page' of that object, not one of first page, since the SLAB
don't use __GFP_COMP when CONFIG_MMU. To get 'struct page' of first page,
we first get a slab and try to get it via virt_to_head_page(slab->s_mem).

Acked-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Signed-off-by: Pekka Enberg <penberg@xxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
mm/slab.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index 2580db0..0b4ddaf 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -930,7 +930,8 @@ 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_head_page(objp);
+ struct slab *slabp = virt_to_slab(objp);
+ struct page *page = virt_to_head_page(slabp->s_mem);
if (PageSlabPfmemalloc(page))
@@ -1776,7 +1777,7 @@ static void *kmem_getpages(struct kmem_cache *cachep, gfp_t flags, int nodeid)
__SetPageSlab(page + i);

if (page->pfmemalloc)
- SetPageSlabPfmemalloc(page + i);
+ SetPageSlabPfmemalloc(page);
memcg_bind_pages(cachep, cachep->gfporder);

@@ -1809,9 +1810,10 @@ static void kmem_freepages(struct kmem_cache *cachep, void *addr)
+ __ClearPageSlabPfmemalloc(page);
while (i--) {
- __ClearPageSlabPfmemalloc(page);

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