[PATCH] mm: slub: Do not take expensive steps for SLUBs speculative high-order allocations

[Mel Gorman]

To avoid locking and per-cpu overhead, SLUB optimisically uses
high-order allocations and falls back to lower allocations if they
fail.  However, by simply trying to allocate, the caller can enter
compaction or reclaim - both of which are likely to cost more than
the benefit of using high-order pages in SLUB. On a desktop system,
two users report that the system is getting locked up with kswapd
using large amounts of CPU. Using SLAB instead of SLUB makes this
problem go away.

This patch prevents SLUB taking any expensive steps when trying to use
high-order allocations. Instead, it is expected to fall back to smaller
orders more aggressively.

Not-signed-off-yet: Mel Gorman <mgorman@xxxxxxx>
---
 mm/page_alloc.c |    3 ++-
 mm/slub.c       |    3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9f8a97b..f160d93 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1972,6 +1972,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
 {
 	int alloc_flags = ALLOC_WMARK_MIN | ALLOC_CPUSET;
 	const gfp_t wait = gfp_mask & __GFP_WAIT;
+	const gfp_t wakes_kswapd = !(gfp_mask & __GFP_NO_KSWAPD);
 
 	/* __GFP_HIGH is assumed to be the same as ALLOC_HIGH to save a branch. */
 	BUILD_BUG_ON(__GFP_HIGH != (__force gfp_t) ALLOC_HIGH);
@@ -1984,7 +1985,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
 	 */
 	alloc_flags |= (__force int) (gfp_mask & __GFP_HIGH);
 
-	if (!wait) {
+	if (!wait && wakes_kswapd) {
 		/*
 		 * Not worth trying to allocate harder for
 		 * __GFP_NOMEMALLOC even if it can't schedule.
diff --git a/mm/slub.c b/mm/slub.c
index 98c358d..1071723 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1170,7 +1170,8 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
 	 * Let the initial higher-order allocation fail under memory pressure
 	 * so we fall-back to the minimum order allocation.
 	 */
-	alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY | __GFP_NO_KSWAPD) & ~__GFP_NOFAIL;
+	alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY | __GFP_NO_KSWAPD) &
+			~(__GFP_NOFAIL | __GFP_WAIT);
 
 	page = alloc_slab_page(alloc_gfp, node, oo);
 	if (unlikely(!page)) {

--vkogqOf2sHV7VnPd--
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/