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Wed, 06 Dec 2023 18:40:13 -0800 (PST) Date: Thu, 7 Dec 2023 11:40:05 +0900 From: Hyeonggon Yoo <42.hyeyoo@gmail.com> To: Vlastimil Babka Cc: David Rientjes , Christoph Lameter , Pekka Enberg , Joonsoo Kim , Andrew Morton , Roman Gushchin , Andrey Ryabinin , Alexander Potapenko , Andrey Konovalov , Dmitry Vyukov , Vincenzo Frascino , Marco Elver , Johannes Weiner , Michal Hocko , Shakeel Butt , Muchun Song , Kees Cook , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, cgroups@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH v2 21/21] mm/slub: optimize free fast path code layout Message-ID: References: <20231120-slab-remove-slab-v2-0-9c9c70177183@suse.cz> <20231120-slab-remove-slab-v2-21-9c9c70177183@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231120-slab-remove-slab-v2-21-9c9c70177183@suse.cz> X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: A359B40005 X-Stat-Signature: cftimzhcmxp4xu6tkx37ju36m9tcinik X-HE-Tag: 1701916815-280145 X-HE-Meta: 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 rdmOIQrM 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Nov 20, 2023 at 07:34:32PM +0100, Vlastimil Babka wrote: > 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 > --- > 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); > } > > > -- Looks good to me, Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com> > 2.42.1 > >