From a8364d5555b2030d093cde0f07951628e55454e1 Mon Sep 17 00:00:00 2001 From: Gilad Ben-Yossef Date: Wed, 28 Mar 2012 14:42:44 -0700 Subject: [PATCH] slub: only IPI CPUs that have per cpu obj to flush flush_all() is called for each kmem_cache_destroy(). So every cache being destroyed dynamically ends up sending an IPI to each CPU in the system, regardless if the cache has ever been used there. For example, if you close the Infinband ipath driver char device file, the close file ops calls kmem_cache_destroy(). So running some infiniband config tool on one a single CPU dedicated to system tasks might interrupt the rest of the 127 CPUs dedicated to some CPU intensive or latency sensitive task. I suspect there is a good chance that every line in the output of "git grep kmem_cache_destroy linux/ | grep '\->'" has a similar scenario. This patch attempts to rectify this issue by sending an IPI to flush the per cpu objects back to the free lists only to CPUs that seem to have such objects. The check which CPU to IPI is racy but we don't care since asking a CPU without per cpu objects to flush does no damage and as far as I can tell the flush_all by itself is racy against allocs on remote CPUs anyway, so if you required the flush_all to be determinstic, you had to arrange for locking regardless. Without this patch the following artificial test case: $ cd /sys/kernel/slab $ for DIR in *; do cat $DIR/alloc_calls > /dev/null; done produces 166 IPIs on an cpuset isolated CPU. With it it produces none. The code path of memory allocation failure for CPUMASK_OFFSTACK=y config was tested using fault injection framework. Signed-off-by: Gilad Ben-Yossef Acked-by: Christoph Lameter Cc: Chris Metcalf Acked-by: Peter Zijlstra Cc: Frederic Weisbecker Cc: Russell King Cc: Pekka Enberg Cc: Matt Mackall Cc: Sasha Levin Cc: Rik van Riel Cc: Andi Kleen Cc: Mel Gorman Cc: Alexander Viro Cc: Avi Kivity Cc: Michal Nazarewicz Cc: Kosaki Motohiro Cc: Milton Miller Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/slub.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/mm/slub.c b/mm/slub.c index f4a6229848fd..dcbb1926cb7f 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2028,9 +2028,17 @@ static void flush_cpu_slab(void *d) __flush_cpu_slab(s, smp_processor_id()); } +static bool has_cpu_slab(int cpu, void *info) +{ + struct kmem_cache *s = info; + struct kmem_cache_cpu *c = per_cpu_ptr(s->cpu_slab, cpu); + + return !!(c->page); +} + static void flush_all(struct kmem_cache *s) { - on_each_cpu(flush_cpu_slab, s, 1); + on_each_cpu_cond(has_cpu_slab, flush_cpu_slab, s, 1, GFP_ATOMIC); } /*