slab: correct pfmemalloc check

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Gitweb:     http://git.infradead.org/?p=mtd-2.6.git;a=commit;h=73293c2f900d0adbb6a415b312cd57976d5ae242
Commit:     73293c2f900d0adbb6a415b312cd57976d5ae242
Parent:     6e4664525b1db28f8c4e1130957f70a94c19213e
Author:     Joonsoo Kim <iamjoonsoo.kim at lge.com>
AuthorDate: Thu Oct 24 10:07:37 2013 +0900
Committer:  Pekka Enberg <penberg at iki.fi>
CommitDate: Thu Oct 24 20:17:19 2013 +0300

    slab: correct pfmemalloc check
    
    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
    pfmemalloc.
    
    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 at linux.intel.com>
    Signed-off-by: Joonsoo Kim <iamjoonsoo.kim at lge.com>
    Signed-off-by: Pekka Enberg <penberg at iki.fi>
---
 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))
 			set_obj_pfmemalloc(&objp);
 	}
@@ -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)
 	else
 		sub_zone_page_state(page_zone(page),
 				NR_SLAB_UNRECLAIMABLE, nr_freed);
+
+	__ClearPageSlabPfmemalloc(page);
 	while (i--) {
 		BUG_ON(!PageSlab(page));
-		__ClearPageSlabPfmemalloc(page);
 		__ClearPageSlab(page);
 		page++;
 	}