From: Roman Gushchin <guro@xxxxxx> 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@xxxxxx: open-code set_page_objcgs() and add some comments, by Johannes] Link: https://lkml.kernel.org/r/20201113001926.GA2934489@xxxxxxxxxxxxxxxxxxxxxxxxxxx [akpm@xxxxxxxxxxxxxxxxxxxx: 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@xxxxxx Signed-off-by: Roman Gushchin <guro@xxxxxx> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: Christoph Lameter <cl@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/memcontrol.h | 19 ------------------- mm/memcontrol.c | 23 +++++++++++++++++++---- mm/slab.c | 2 +- mm/slab.h | 14 ++++++++++---- mm/slub.c | 2 +- 5 files changed, 31 insertions(+), 29 deletions(-) --- a/include/linux/memcontrol.h~mm-memcg-slab-pre-allocate-obj_cgroups-for-slab-caches-with-slab_account +++ a/include/linux/memcontrol.h @@ -475,19 +475,6 @@ static inline struct obj_cgroup **page_o return (struct obj_cgroup **)(memcg_data & ~MEMCG_DATA_FLAGS_MASK); } -/* - * set_page_objcgs - associate a page with a object cgroups vector - * @page: a pointer to the page struct - * @objcgs: a pointer to the object cgroups vector - * - * Atomically associates a page with a vector of object cgroups. - */ -static inline bool set_page_objcgs(struct page *page, - struct obj_cgroup **objcgs) -{ - return !cmpxchg(&page->memcg_data, 0, (unsigned long)objcgs | - MEMCG_DATA_OBJCGS); -} #else static inline struct obj_cgroup **page_objcgs(struct page *page) { @@ -498,12 +485,6 @@ static inline struct obj_cgroup **page_o { return NULL; } - -static inline bool set_page_objcgs(struct page *page, - struct obj_cgroup **objcgs) -{ - return true; -} #endif static __always_inline bool memcg_stat_item_in_bytes(int idx) --- a/mm/memcontrol.c~mm-memcg-slab-pre-allocate-obj_cgroups-for-slab-caches-with-slab_account +++ a/mm/memcontrol.c @@ -2935,9 +2935,10 @@ static void commit_charge(struct page *p #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 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; } --- a/mm/slab.c~mm-memcg-slab-pre-allocate-obj_cgroups-for-slab-caches-with-slab_account +++ a/mm/slab.c @@ -1379,7 +1379,7 @@ static struct page *kmem_getpages(struct return NULL; } - account_slab_page(page, cachep->gfporder, cachep); + account_slab_page(page, cachep->gfporder, cachep, flags); __SetPageSlab(page); /* Record if ALLOC_NO_WATERMARKS was set when allocating the slab */ if (sk_memalloc_socks() && page_is_pfmemalloc(page)) --- a/mm/slab.h~mm-memcg-slab-pre-allocate-obj_cgroups-for-slab-caches-with-slab_account +++ a/mm/slab.h @@ -238,7 +238,7 @@ static inline bool kmem_cache_debug_flag #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); static inline void memcg_free_page_obj_cgroups(struct page *page) { @@ -315,7 +315,8 @@ static inline void memcg_slab_post_alloc page = virt_to_head_page(p[i]); if (!page_objcgs(page) && - memcg_alloc_page_obj_cgroups(page, s, flags)) { + memcg_alloc_page_obj_cgroups(page, s, flags, + false)) { obj_cgroup_uncharge(objcg, obj_full_size(s)); continue; } @@ -379,7 +380,8 @@ static inline struct mem_cgroup *memcg_f } static inline int memcg_alloc_page_obj_cgroups(struct page *page, - struct kmem_cache *s, gfp_t gfp) + struct kmem_cache *s, gfp_t gfp, + bool new_page) { return 0; } @@ -420,8 +422,12 @@ static inline struct kmem_cache *virt_to } static __always_inline void account_slab_page(struct page *page, int order, - struct kmem_cache *s) + struct kmem_cache *s, + gfp_t gfp) { + if (memcg_kmem_enabled() && (s->flags & SLAB_ACCOUNT)) + memcg_alloc_page_obj_cgroups(page, s, gfp, true); + mod_node_page_state(page_pgdat(page), cache_vmstat_idx(s), PAGE_SIZE << order); } --- a/mm/slub.c~mm-memcg-slab-pre-allocate-obj_cgroups-for-slab-caches-with-slab_account +++ a/mm/slub.c @@ -1785,7 +1785,7 @@ static struct page *allocate_slab(struct page->objects = oo_objects(oo); - account_slab_page(page, oo_order(oo), s); + account_slab_page(page, oo_order(oo), s, flags); page->slab_cache = s; __SetPageSlab(page); _
