There is no consideration for pfmemalloc_match() in get_partial(). If we don't consider that, we can't restrict access to PFMEMALLOC page mostly.
We may encounter following scenario. Assume there is a request from normal allocation and there is no objects in per cpu cache and no node partial slab. In this case, slab_alloc go into slow-path and new_slab_objects() is invoked. It may return PFMEMALLOC page. Current user is not allowed to access PFMEMALLOC page, deactivate_slab() is called (commit 5091b74a95d447e34530e713a8971450a45498b3), then return object from PFMEMALLOC page. Next time, when we meet another request from normal allocation, slab_alloc() go into slow-path and re-go new_slab_objects(). In new_slab_objects(), we invoke get_partial() and we get a partial slab which we have been deactivated just before, that is, PFMEMALLOC page. We extract one object from it and re-deactivate. "deactivate -> re-get in get_partial -> re-deactivate" occures repeatedly. As a result, we can't restrict access to PFMEMALLOC page and moreover, it introduce much performance degration to normal allocation because of deactivation frequently. Now, we need to consider pfmemalloc_match() in get_partial_node() It prevent "deactivate -> re-get in get_partial". Instead, new_slab() is called. It may return !PFMEMALLOC page, so above situation will be suspended sometime. Signed-off-by: Joonsoo Kim <js1...@gmail.com> Cc: David Miller <da...@davemloft.net> Cc: Neil Brown <ne...@suse.de> Cc: Peter Zijlstra <a.p.zijls...@chello.nl> Cc: Mike Christie <micha...@cs.wisc.edu> Cc: Eric B Munson <emun...@mgebm.net> Cc: Eric Dumazet <eric.duma...@gmail.com> Cc: Sebastian Andrzej Siewior <sebast...@breakpoint.cc> Cc: Mel Gorman <mgor...@suse.de> Cc: Christoph Lameter <c...@linux-foundation.org> Cc: Andrew Morton <a...@linux-foundation.org> --- This patch based on Pekka's slab/next tree with my two patches. [PATCH 1/2] slub: rename cpu_partial to max_cpu_object https://lkml.org/lkml/2012/8/24/293 [PATCH 2/2] slub: correct the calculation of the number of cpu objects in get_partial_node https://lkml.org/lkml/2012/8/24/290 diff --git a/mm/slub.c b/mm/slub.c index c96e0e4..a21da3a 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -1529,12 +1529,13 @@ static inline void *acquire_slab(struct kmem_cache *s, } static int put_cpu_partial(struct kmem_cache *s, struct page *page, int drain); +static inline bool pfmemalloc_match(struct page *page, gfp_t gfpflags); /* * Try to allocate a partial slab from a specific node. */ -static void *get_partial_node(struct kmem_cache *s, - struct kmem_cache_node *n, struct kmem_cache_cpu *c) +static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n, + struct kmem_cache_cpu *c, gfp_t flags) { struct page *page, *page2; void *object = NULL; @@ -1551,8 +1552,12 @@ static void *get_partial_node(struct kmem_cache *s, spin_lock(&n->list_lock); list_for_each_entry_safe(page, page2, &n->partial, lru) { - void *t = acquire_slab(s, n, page, object == NULL); + void *t; + if (!pfmemalloc_match(page, flags)) + continue; + + t = acquire_slab(s, n, page, object == NULL); if (!t) break; @@ -1620,7 +1625,7 @@ static void *get_any_partial(struct kmem_cache *s, gfp_t flags, if (n && cpuset_zone_allowed_hardwall(zone, flags) && n->nr_partial > s->min_partial) { - object = get_partial_node(s, n, c); + object = get_partial_node(s, n, c, flags); if (object) { /* * Return the object even if @@ -1649,7 +1654,7 @@ static void *get_partial(struct kmem_cache *s, gfp_t flags, int node, void *object; int searchnode = (node == NUMA_NO_NODE) ? numa_node_id() : node; - object = get_partial_node(s, get_node(s, searchnode), c); + object = get_partial_node(s, get_node(s, searchnode), c, flags); if (object || node != NUMA_NO_NODE) return object; -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
