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b=KIzxc26DhH1045e+ExrzClszygTXStN9ECH4U/XdwnS8Yusfg53YVrEKplbAB88oc 4X+Df9BjB+OdTt+/vJnXkTl4OX5SBWervBjCoAA748KRgWIZhdBX/djV/P7R8F1YM/ tIsk4nrzCIQ1zt8B/G5PRTp/VhZHNtwvuUhscDZsaHynVXz3lybUDVJRWT842UFc5I H8DRaiXxjTn0fWntsAXEQq0EPBS4RMl0wgaTYpU1fHKm1VIZAkmg2bjW3Em7oGJfA8 LZT3aAjEa3WdIoDoB+W6P0Scq2wxGAktVuXYVe9SBwmjsnNgQS5VD5Cy3uV/D2FTaX MUHPhfGNWXbng== From: "Vlastimil Babka (SUSE)" Date: Mon, 20 Jul 2026 16:16:27 +0200 Subject: [PATCH v2 13/13] mm/slab: stop allocating objcg pointers when unnecessary MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260720-b4-objext_split-v2-13-2fa7c6f60dbe@kernel.org> References: <20260720-b4-objext_split-v2-0-2fa7c6f60dbe@kernel.org> In-Reply-To: <20260720-b4-objext_split-v2-0-2fa7c6f60dbe@kernel.org> To: Harry Yoo , Suren Baghdasaryan Cc: Hao Li , Shakeel Butt , Alexander Potapenko , Marco Elver , Andrew Morton , Christoph Lameter , David Rientjes , Roman Gushchin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, "Vlastimil Babka (SUSE)" X-Mailer: b4 0.15.2 X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 4E26380010 X-Stat-Signature: y8wof353nrxsixbba7sby7put1yz6btj X-Rspam-User: X-HE-Tag: 1784557029-325388 X-HE-Meta: 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 RimE304a +dylerhLLPNzr09u1at2+tfKn8GycRZn+xdNN/LtrgdI8++nu5qoRTfRHH7o+ep7nrwGnnevj5nWljbk2T1UByGB1LFm5rDaVcQ+20wwRcHEuOFVJ1CRyAWqz6SLsiCCom2OVtzgBBNL5jH1C+Bd9AcX64mKMMo4+es/5qRwS36Ek3+hbgUBPh/KMJ1TTNFqHfd5l3SlUFJA5iWPouN4WyMO1K+BzXP19sDsmJ1h36rlFZ1FHrAhIzRYwyw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Start using the slab_needs_objcg() helper to calculate slabobj_ext size. Caches that we know to never need objcg pointers (currently KMALLOC_NORMAL caches) will thus stop wasting memory on them when memory allocation profiling is enabled. For things to work properly, we need to also add slab_needs_objcg() checks to mem_cgroup_from_obj_slab() and memcg_slab_free_hook(), because when obj_exts array exists for a slab only due to mem_alloc profiling, we would otherwise attempt to access a non-existing objcg pointer in that slab. The function __memcg_slab_post_alloc_hook() should not be possible to call for a slab where slab_needs_objcg() is false, but add a DEBUG_VM check there to prevent breaking this assumption accidentally. Signed-off-by: Vlastimil Babka (SUSE) --- mm/memcontrol.c | 6 ++++++ mm/slab.h | 14 +++++++++++--- mm/slub.c | 3 +++ 3 files changed, 20 insertions(+), 3 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index cb1e97b4edc1..aace85fb99f9 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2871,6 +2871,9 @@ struct mem_cgroup *mem_cgroup_from_obj_slab(struct slab *slab, void *p) if (!obj_exts) return NULL; + if (!slab_needs_objcg(slab)) + return NULL; + get_slab_obj_exts(obj_exts); obj_ext = slab_obj_ext(slab->slab_cache, slab, obj_exts, p); objcg = slab_obj_ext_objcg(obj_ext); @@ -3580,6 +3583,9 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru, slab = virt_to_slab(p[i]); + if (IS_ENABLED(CONFIG_DEBUG_VM) && WARN_ON_ONCE(!slab_needs_objcg(slab))) + continue; + if (!slab_obj_exts(slab) && alloc_slab_obj_exts(slab, s, flags, slab_alloc_flags)) { continue; diff --git a/mm/slab.h b/mm/slab.h index 65b44902c06e..18c2a807f023 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -615,7 +615,7 @@ static inline size_t cache_obj_ext_size(struct kmem_cache *s) { size_t sz = 0; - if (IS_ENABLED(CONFIG_MEMCG)) + if (cache_needs_objcg(s)) sz += 1; if (slab_obj_ext_has_codetag()) @@ -626,7 +626,15 @@ static inline size_t cache_obj_ext_size(struct kmem_cache *s) static inline size_t slab_obj_ext_size(struct slab *slab) { - return cache_obj_ext_size(slab->slab_cache); + size_t sz = 0; + + if (slab_needs_objcg(slab)) + sz += 1; + + if (slab_obj_ext_has_codetag()) + sz += 1; + + return sizeof(struct slabobj_ext) * sz; } #ifdef CONFIG_SLAB_OBJ_EXT @@ -753,7 +761,7 @@ static inline void slab_obj_ext_set_objcg(struct slabobj_ext *obj_ext, static inline union codetag_ref * slab_obj_ext_codetag_ref(struct slab *slab, struct slabobj_ext *obj_ext) { - if (IS_ENABLED(CONFIG_MEMCG)) + if (slab_needs_objcg(slab)) obj_ext += 1; return &obj_ext->_ctref; diff --git a/mm/slub.c b/mm/slub.c index 30435e2509ea..e6148b73b92f 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2512,6 +2512,9 @@ void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p, if (likely(!obj_exts)) return; + if (!slab_needs_objcg(slab)) + return; + get_slab_obj_exts(obj_exts); __memcg_slab_free_hook(s, slab, p, objects, obj_exts); put_slab_obj_exts(obj_exts); -- 2.55.0