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Date: Mon, 20 Nov 2023 19:34:32 +0100 From: Vlastimil Babka <vbabka@...e.cz> To: David Rientjes <rientjes@...gle.com>, Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>, Joonsoo Kim <iamjoonsoo.kim@....com> Cc: Andrew Morton <akpm@...ux-foundation.org>, Hyeonggon Yoo <42.hyeyoo@...il.com>, Roman Gushchin <roman.gushchin@...ux.dev>, Andrey Ryabinin <ryabinin.a.a@...il.com>, Alexander Potapenko <glider@...gle.com>, Andrey Konovalov <andreyknvl@...il.com>, Dmitry Vyukov <dvyukov@...gle.com>, Vincenzo Frascino <vincenzo.frascino@....com>, Marco Elver <elver@...gle.com>, Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, Shakeel Butt <shakeelb@...gle.com>, Muchun Song <muchun.song@...ux.dev>, Kees Cook <keescook@...omium.org>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com, cgroups@...r.kernel.org, linux-hardening@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz> Subject: [PATCH v2 21/21] mm/slub: optimize free fast path code layout Inspection of kmem_cache_free() disassembly showed we could make the fast path smaller by providing few more hints to the compiler, and splitting the memcg_slab_free_hook() into an inline part that only checks if there's work to do, and an out of line part doing the actual uncharge. bloat-o-meter results: add/remove: 2/0 grow/shrink: 0/3 up/down: 286/-554 (-268) Function old new delta __memcg_slab_free_hook - 270 +270 __pfx___memcg_slab_free_hook - 16 +16 kfree 828 665 -163 kmem_cache_free 1116 948 -168 kmem_cache_free_bulk.part 1701 1478 -223 Checking kmem_cache_free() disassembly now shows the non-fastpath cases are handled out of line, which should reduce instruction cache usage. Signed-off-by: Vlastimil Babka <vbabka@...e.cz> --- mm/slub.c | 40 ++++++++++++++++++++++++---------------- 1 file changed, 24 insertions(+), 16 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 77d259f3d592..3f8b95757106 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -1959,20 +1959,11 @@ void memcg_slab_post_alloc_hook(struct kmem_cache *s, struct obj_cgroup *objcg, return __memcg_slab_post_alloc_hook(s, objcg, flags, size, p); } -static inline void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab, - void **p, int objects) +static void __memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab, + void **p, int objects, + struct obj_cgroup **objcgs) { - struct obj_cgroup **objcgs; - int i; - - if (!memcg_kmem_online()) - return; - - objcgs = slab_objcgs(slab); - if (!objcgs) - return; - - for (i = 0; i < objects; i++) { + for (int i = 0; i < objects; i++) { struct obj_cgroup *objcg; unsigned int off; @@ -1988,6 +1979,22 @@ static inline void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab, obj_cgroup_put(objcg); } } + +static __fastpath_inline +void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p, + int objects) +{ + struct obj_cgroup **objcgs; + + if (!memcg_kmem_online()) + return; + + objcgs = slab_objcgs(slab); + if (likely(!objcgs)) + return; + + __memcg_slab_free_hook(s, slab, p, objects, objcgs); +} #else /* CONFIG_MEMCG_KMEM */ static inline struct mem_cgroup *memcg_from_slab_obj(void *ptr) { @@ -2047,7 +2054,7 @@ static __always_inline bool slab_free_hook(struct kmem_cache *s, * The initialization memset's clear the object and the metadata, * but don't touch the SLAB redzone. */ - if (init) { + if (unlikely(init)) { int rsize; if (!kasan_has_integrated_init()) @@ -2083,7 +2090,8 @@ static inline bool slab_free_freelist_hook(struct kmem_cache *s, next = get_freepointer(s, object); /* If object's reuse doesn't have to be delayed */ - if (!slab_free_hook(s, object, slab_want_init_on_free(s))) { + if (likely(!slab_free_hook(s, object, + slab_want_init_on_free(s)))) { /* Move object to the new freelist */ set_freepointer(s, object, *head); *head = object; @@ -4282,7 +4290,7 @@ static __fastpath_inline void slab_free(struct kmem_cache *s, struct slab *slab, * With KASAN enabled slab_free_freelist_hook modifies the freelist * to remove objects, whose reuse must be delayed. */ - if (slab_free_freelist_hook(s, &head, &tail, &cnt)) + if (likely(slab_free_freelist_hook(s, &head, &tail, &cnt))) do_slab_free(s, slab, head, tail, cnt, addr); } -- 2.42.1
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