From b77d5b1b83e3e14870224de7c63f115a2dc44e9a Mon Sep 17 00:00:00 2001 From: Muchun Song Date: Fri, 29 Apr 2022 20:30:44 +0800 Subject: [PATCH] mm: slab: optimize memcg_slab_free_hook() Most callers of memcg_slab_free_hook() already know the slab, which could be passed to memcg_slab_free_hook() directly to reduce the overhead of an another call of virt_to_slab(). For bulk freeing of objects, the call of slab_objcgs() in the loop in memcg_slab_free_hook() is redundant as well. Rework memcg_slab_free_hook() and build_detached_freelist() to reduce those unnecessary overhead and make memcg_slab_free_hook() can handle bulk freeing in slab_free(). Move the calling site of memcg_slab_free_hook() from do_slab_free() to slab_free() for slub to make the code clearer since the logic is weird (e.g. the caller need to judge whether it needs to call memcg_slab_free_hook()). It is easy to make mistakes like missing calling of memcg_slab_free_hook() like fixes of: commit d1b2cf6cb84a ("mm: memcg/slab: uncharge during kmem_cache_free_bulk()") commit ae085d7f9365 ("mm: kfence: fix missing objcg housekeeping for SLAB") This optimization is mainly for bulk objects freeing. The following numbers is shown for 16-object freeing. before after kmem_cache_free_bulk: ~430 ns ~400 ns The overhead is reduced by about 7% for 16-object freeing. Signed-off-by: Muchun Song Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com> Link: https://lore.kernel.org/r/20220429123044.37885-1-songmuchun@bytedance.com Signed-off-by: Vlastimil Babka --- mm/slab.c | 4 ++-- mm/slab.h | 30 +++++++------------------ mm/slub.c | 66 +++++++++++++++++++------------------------------------ 3 files changed, 32 insertions(+), 68 deletions(-) diff --git a/mm/slab.c b/mm/slab.c index f7d6ca702018..764cbadba69c 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -3406,9 +3406,10 @@ static __always_inline void __cache_free(struct kmem_cache *cachep, void *objp, { bool init; + memcg_slab_free_hook(cachep, virt_to_slab(objp), &objp, 1); + if (is_kfence_address(objp)) { kmemleak_free_recursive(objp, cachep->flags); - memcg_slab_free_hook(cachep, &objp, 1); __kfence_free(objp); return; } @@ -3441,7 +3442,6 @@ void ___cache_free(struct kmem_cache *cachep, void *objp, check_irq_off(); kmemleak_free_recursive(objp, cachep->flags); objp = cache_free_debugcheck(cachep, objp, caller); - memcg_slab_free_hook(cachep, &objp, 1); /* * Skip calling cache_free_alien() when the platform is not numa. diff --git a/mm/slab.h b/mm/slab.h index db9fb5c8dae7..a8d5eb1c323f 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -547,36 +547,22 @@ static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s, obj_cgroup_put(objcg); } -static inline void memcg_slab_free_hook(struct kmem_cache *s_orig, +static inline void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p, int objects) { - struct kmem_cache *s; struct obj_cgroup **objcgs; - struct obj_cgroup *objcg; - struct slab *slab; - unsigned int off; int i; if (!memcg_kmem_enabled()) return; + objcgs = slab_objcgs(slab); + if (!objcgs) + return; + for (i = 0; i < objects; i++) { - if (unlikely(!p[i])) - continue; - - slab = virt_to_slab(p[i]); - /* we could be given a kmalloc_large() object, skip those */ - if (!slab) - continue; - - objcgs = slab_objcgs(slab); - if (!objcgs) - continue; - - if (!s_orig) - s = slab->slab_cache; - else - s = s_orig; + struct obj_cgroup *objcg; + unsigned int off; off = obj_to_index(s, slab, p[i]); objcg = objcgs[off]; @@ -628,7 +614,7 @@ static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s, { } -static inline void memcg_slab_free_hook(struct kmem_cache *s, +static inline void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p, int objects) { } diff --git a/mm/slub.c b/mm/slub.c index 514741cd1c3c..26b00951aad1 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -3464,9 +3464,6 @@ static __always_inline void do_slab_free(struct kmem_cache *s, struct kmem_cache_cpu *c; unsigned long tid; - /* memcg_slab_free_hook() is already called for bulk free. */ - if (!tail) - memcg_slab_free_hook(s, &head, 1); redo: /* * Determine the currently cpus per cpu slab. @@ -3526,9 +3523,10 @@ redo: } static __always_inline void slab_free(struct kmem_cache *s, struct slab *slab, - void *head, void *tail, int cnt, + void *head, void *tail, void **p, int cnt, unsigned long addr) { + memcg_slab_free_hook(s, slab, p, cnt); /* * With KASAN enabled slab_free_freelist_hook modifies the freelist * to remove objects, whose reuse must be delayed. @@ -3550,7 +3548,7 @@ void kmem_cache_free(struct kmem_cache *s, void *x) if (!s) return; trace_kmem_cache_free(_RET_IP_, x, s->name); - slab_free(s, virt_to_slab(x), x, NULL, 1, _RET_IP_); + slab_free(s, virt_to_slab(x), x, NULL, &x, 1, _RET_IP_); } EXPORT_SYMBOL(kmem_cache_free); @@ -3591,79 +3589,59 @@ static inline int build_detached_freelist(struct kmem_cache *s, size_t size, void **p, struct detached_freelist *df) { - size_t first_skipped_index = 0; int lookahead = 3; void *object; struct folio *folio; - struct slab *slab; - - /* Always re-init detached_freelist */ - df->slab = NULL; - - do { - object = p[--size]; - /* Do we need !ZERO_OR_NULL_PTR(object) here? (for kfree) */ - } while (!object && size); - - if (!object) - return 0; + size_t same; + object = p[--size]; folio = virt_to_folio(object); if (!s) { /* Handle kalloc'ed objects */ if (unlikely(!folio_test_slab(folio))) { free_large_kmalloc(folio, object); - p[size] = NULL; /* mark object processed */ + df->slab = NULL; return size; } /* Derive kmem_cache from object */ - slab = folio_slab(folio); - df->s = slab->slab_cache; + df->slab = folio_slab(folio); + df->s = df->slab->slab_cache; } else { - slab = folio_slab(folio); + df->slab = folio_slab(folio); df->s = cache_from_obj(s, object); /* Support for memcg */ } - if (is_kfence_address(object)) { - slab_free_hook(df->s, object, false); - __kfence_free(object); - p[size] = NULL; /* mark object processed */ - return size; - } - /* Start new detached freelist */ - df->slab = slab; - set_freepointer(df->s, object, NULL); df->tail = object; df->freelist = object; - p[size] = NULL; /* mark object processed */ df->cnt = 1; + if (is_kfence_address(object)) + return size; + + set_freepointer(df->s, object, NULL); + + same = size; while (size) { object = p[--size]; - if (!object) - continue; /* Skip processed objects */ - /* df->slab is always set at this point */ if (df->slab == virt_to_slab(object)) { /* Opportunity build freelist */ set_freepointer(df->s, object, df->freelist); df->freelist = object; df->cnt++; - p[size] = NULL; /* mark object processed */ - + same--; + if (size != same) + swap(p[size], p[same]); continue; } /* Limit look ahead search */ if (!--lookahead) break; - - if (!first_skipped_index) - first_skipped_index = size + 1; } - return first_skipped_index; + return same; } /* Note that interrupts must be enabled when calling this function. */ @@ -3672,7 +3650,6 @@ void kmem_cache_free_bulk(struct kmem_cache *s, size_t size, void **p) if (WARN_ON(!size)) return; - memcg_slab_free_hook(s, p, size); do { struct detached_freelist df; @@ -3680,7 +3657,8 @@ void kmem_cache_free_bulk(struct kmem_cache *s, size_t size, void **p) if (!df.slab) continue; - slab_free(df.s, df.slab, df.freelist, df.tail, df.cnt, _RET_IP_); + slab_free(df.s, df.slab, df.freelist, df.tail, &p[size], df.cnt, + _RET_IP_); } while (likely(size)); } EXPORT_SYMBOL(kmem_cache_free_bulk); @@ -4581,7 +4559,7 @@ void kfree(const void *x) return; } slab = folio_slab(folio); - slab_free(slab->slab_cache, slab, object, NULL, 1, _RET_IP_); + slab_free(slab->slab_cache, slab, object, NULL, &object, 1, _RET_IP_); } EXPORT_SYMBOL(kfree);