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. [[email protected]: Original implementation and problem identification] Signed-off-by: Mel Gorman <[email protected]> --- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
