From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0E2D242B726; Mon, 20 Jul 2026 14:17:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784557030; cv=none; b=h4getuWQJV4yGDCDyBd/LNI3XQs7RJLN73xSswESLLnujk3u6H8jU6i+Ia/8LlW/Oq5xyjlSptmtuN4iLZvdWKZS2CNcp1buTPcpujvF29PkBePuTBZVL6WkMdufTRMD4EPEWu1ib6cnr7Ev/x1d71QXvLwNJXpfz+XSxcTwZVk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784557030; c=relaxed/simple; bh=ebUJQq50hWtJS9nsVENCUjdOnHucNEhidB+p61SyW3c=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=MFH+SRehte1HV8TW2Satxf0hJs0Ch692gWoNQygQfX52UNb6RsQoUgoIWwxNc9+1VbLKvr8v31Pb+21fqh3bqFusRPiyNhBKZ4PgFYPDm9lGx/4E+zsigs0c4DVkbDEPQ2sjslU6LI+iZ3x6em83tSUAn+LC4vDqlyv0Ym3dFUo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=KIzxc26D; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="KIzxc26D" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 080271F000E9; Mon, 20 Jul 2026 14:17:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784557028; bh=zNnHaVXxj/mvFCRCqUFR4sjoNHHhPJC/qg6efDIn92M=; h=From:Date:Subject:References:In-Reply-To:To:Cc; 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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