From 43d77867a4f333de4e4189114c480dd365133c09 Mon Sep 17 00:00:00 2001 From: Joonsoo Kim Date: Sat, 9 Jun 2012 02:23:16 +0900 Subject: [PATCH] slub: refactoring unfreeze_partials() Current implementation of unfreeze_partials() is so complicated, but benefit from it is insignificant. In addition many code in do {} while loop have a bad influence to a fail rate of cmpxchg_double_slab. Under current implementation which test status of cpu partial slab and acquire list_lock in do {} while loop, we don't need to acquire a list_lock and gain a little benefit when front of the cpu partial slab is to be discarded, but this is a rare case. In case that add_partial is performed and cmpxchg_double_slab is failed, remove_partial should be called case by case. I think that these are disadvantages of current implementation, so I do refactoring unfreeze_partials(). Minimizing code in do {} while loop introduce a reduced fail rate of cmpxchg_double_slab. Below is output of 'slabinfo -r kmalloc-256' when './perf stat -r 33 hackbench 50 process 4000 > /dev/null' is done. ** before ** Cmpxchg_double Looping ------------------------ Locked Cmpxchg Double redos 182685 Unlocked Cmpxchg Double redos 0 ** after ** Cmpxchg_double Looping ------------------------ Locked Cmpxchg Double redos 177995 Unlocked Cmpxchg Double redos 1 We can see cmpxchg_double_slab fail rate is improved slightly. Bolow is output of './perf stat -r 30 hackbench 50 process 4000 > /dev/null'. ** before ** Performance counter stats for './hackbench 50 process 4000' (30 runs): 108517.190463 task-clock # 7.926 CPUs utilized ( +- 0.24% ) 2,919,550 context-switches # 0.027 M/sec ( +- 3.07% ) 100,774 CPU-migrations # 0.929 K/sec ( +- 4.72% ) 124,201 page-faults # 0.001 M/sec ( +- 0.15% ) 401,500,234,387 cycles # 3.700 GHz ( +- 0.24% ) stalled-cycles-frontend stalled-cycles-backend 250,576,913,354 instructions # 0.62 insns per cycle ( +- 0.13% ) 45,934,956,860 branches # 423.297 M/sec ( +- 0.14% ) 188,219,787 branch-misses # 0.41% of all branches ( +- 0.56% ) 13.691837307 seconds time elapsed ( +- 0.24% ) ** after ** Performance counter stats for './hackbench 50 process 4000' (30 runs): 107784.479767 task-clock # 7.928 CPUs utilized ( +- 0.22% ) 2,834,781 context-switches # 0.026 M/sec ( +- 2.33% ) 93,083 CPU-migrations # 0.864 K/sec ( +- 3.45% ) 123,967 page-faults # 0.001 M/sec ( +- 0.15% ) 398,781,421,836 cycles # 3.700 GHz ( +- 0.22% ) stalled-cycles-frontend stalled-cycles-backend 250,189,160,419 instructions # 0.63 insns per cycle ( +- 0.09% ) 45,855,370,128 branches # 425.436 M/sec ( +- 0.10% ) 169,881,248 branch-misses # 0.37% of all branches ( +- 0.43% ) 13.596272341 seconds time elapsed ( +- 0.22% ) No regression is found, but rather we can see slightly better result. Acked-by: Christoph Lameter Signed-off-by: Joonsoo Kim Signed-off-by: Pekka Enberg --- mm/slub.c | 48 ++++++++++++++---------------------------------- 1 file changed, 14 insertions(+), 34 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 4f406cd899b7..f96d8bcec54f 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -1879,18 +1879,24 @@ redo: */ static void unfreeze_partials(struct kmem_cache *s) { - struct kmem_cache_node *n = NULL; + struct kmem_cache_node *n = NULL, *n2 = NULL; struct kmem_cache_cpu *c = this_cpu_ptr(s->cpu_slab); struct page *page, *discard_page = NULL; while ((page = c->partial)) { - enum slab_modes { M_PARTIAL, M_FREE }; - enum slab_modes l, m; struct page new; struct page old; c->partial = page->next; - l = M_FREE; + + n2 = get_node(s, page_to_nid(page)); + if (n != n2) { + if (n) + spin_unlock(&n->list_lock); + + n = n2; + spin_lock(&n->list_lock); + } do { @@ -1903,43 +1909,17 @@ static void unfreeze_partials(struct kmem_cache *s) new.frozen = 0; - if (!new.inuse && (!n || n->nr_partial > s->min_partial)) - m = M_FREE; - else { - struct kmem_cache_node *n2 = get_node(s, - page_to_nid(page)); - - m = M_PARTIAL; - if (n != n2) { - if (n) - spin_unlock(&n->list_lock); - - n = n2; - spin_lock(&n->list_lock); - } - } - - if (l != m) { - if (l == M_PARTIAL) { - remove_partial(n, page); - stat(s, FREE_REMOVE_PARTIAL); - } else { - add_partial(n, page, - DEACTIVATE_TO_TAIL); - stat(s, FREE_ADD_PARTIAL); - } - - l = m; - } - } while (!__cmpxchg_double_slab(s, page, old.freelist, old.counters, new.freelist, new.counters, "unfreezing slab")); - if (m == M_FREE) { + if (unlikely(!new.inuse && n->nr_partial > s->min_partial)) { page->next = discard_page; discard_page = page; + } else { + add_partial(n, page, DEACTIVATE_TO_TAIL); + stat(s, FREE_ADD_PARTIAL); } } -- 2.20.1