From 2e9bd483159939ed2c0704b914294653c8341d25 Mon Sep 17 00:00:00 2001 From: Roman Gushchin Date: Wed, 24 Feb 2021 12:03:11 -0800 Subject: mm: memcg/slab: pre-allocate obj_cgroups for slab caches with SLAB_ACCOUNT In general it's unknown in advance if a slab page will contain accounted objects or not. In order to avoid memory waste, an obj_cgroup vector is allocated dynamically when a need to account of a new object arises. Such approach is memory efficient, but requires an expensive cmpxchg() to set up the memcg/objcgs pointer, because an allocation can race with a different allocation on another cpu. But in some common cases it's known for sure that a slab page will contain accounted objects: if the page belongs to a slab cache with a SLAB_ACCOUNT flag set. It includes such popular objects like vm_area_struct, anon_vma, task_struct, etc. In such cases we can pre-allocate the objcgs vector and simple assign it to the page without any atomic operations, because at this early stage the page is not visible to anyone else. A very simplistic benchmark (allocating 10000000 64-bytes objects in a row) shows ~15% win. In the real life it seems that most workloads are not very sensitive to the speed of (accounted) slab allocations. [guro@fb.com: open-code set_page_objcgs() and add some comments, by Johannes] Link: https://lkml.kernel.org/r/20201113001926.GA2934489@carbon.dhcp.thefacebook.com [akpm@linux-foundation.org: fix it for mm-slub-call-account_slab_page-after-slab-page-initialization-fix.patch] Link: https://lkml.kernel.org/r/20201110195753.530157-2-guro@fb.com Signed-off-by: Roman Gushchin Acked-by: Johannes Weiner Reviewed-by: Shakeel Butt Cc: Michal Hocko Cc: Christoph Lameter Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/memcontrol.c | 23 +++++++++++++++++++---- 1 file changed, 19 insertions(+), 4 deletions(-) (limited to 'mm/memcontrol.c') diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 0b9bd354e97e..60ce452e42e6 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2935,9 +2935,10 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg) #ifdef CONFIG_MEMCG_KMEM int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s, - gfp_t gfp) + gfp_t gfp, bool new_page) { unsigned int objects = objs_per_slab_page(s, page); + unsigned long memcg_data; void *vec; vec = kcalloc_node(objects, sizeof(struct obj_cgroup *), gfp, @@ -2945,11 +2946,25 @@ int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s, if (!vec) return -ENOMEM; - if (!set_page_objcgs(page, vec)) + memcg_data = (unsigned long) vec | MEMCG_DATA_OBJCGS; + if (new_page) { + /* + * If the slab page is brand new and nobody can yet access + * it's memcg_data, no synchronization is required and + * memcg_data can be simply assigned. + */ + page->memcg_data = memcg_data; + } else if (cmpxchg(&page->memcg_data, 0, memcg_data)) { + /* + * If the slab page is already in use, somebody can allocate + * and assign obj_cgroups in parallel. In this case the existing + * objcg vector should be reused. + */ kfree(vec); - else - kmemleak_not_leak(vec); + return 0; + } + kmemleak_not_leak(vec); return 0; } -- cgit