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 9057243F4BE; Wed, 15 Jul 2026 10:11:25 +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=1784110286; cv=none; b=GU2xHX4TKJ8BoAiJazN1unYUubBffC6Ta5B4oI80izDUtekIDlwqaO3sfi1TB5pfzHa+HOeZyMbDNDmGPHt/4h+YSfPYod8CAaGMfhc0JoZ2frT683FMNqlSX3iPBK/BwxJqsoBoFzYmGYWPtTlpFZqoXGB1qi/YtEhafVOBvXc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784110286; c=relaxed/simple; bh=O0CIznq26Ds2kUKsMvzrT8Dx5jQK5mnuzi2ty7qEc0g=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=HW/ggma22lmkTOrelZPYw1j+J6MWy4hpqDc6QB0duZRkDedNEHHOBYHVNwYWPqqv5ima3xBY3r60wgnGXi8xK+ASNFaJT0thW++rX0EERbqK217BDJBE16lym8fRISY2vYZma5MmRU3w/Y2ESXuI2FejRYbmQuOMIYxB+MGsfR4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=lGHDqt5V; 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="lGHDqt5V" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 831751F00A3A; Wed, 15 Jul 2026 10:11:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784110285; bh=sxiKNmbJD7zBEkDQUyHwImzWMYztIT9SravkSnuQT8g=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=lGHDqt5VwPjEwT8kk2s3Ys3pWyu6FyVPdbFgHVC0vlQvErAZH6PxAPutt7waAvKb1 sPYK5/rI9F0AP/MopFYh0hscAsBpuqgr9stRYMtsJLwEx5cZFa2CqqG2BtumyMr4RQ /hdyfFlwdEVyK6CqDt6Aw3di232txGDH7dTfQYIH4cBQr03QpcwYOFZFhSRChqb3QA oKJxtdn3g/R09HDdzGF+jWLF6W1mxKlW5KU5aG4hwofplZUCD62EZib4C+NScRzNck jrdi2vF5fS7y4GuXcuUiRVEi3CLpi8hW41rXZHlemscDJhmv5TF+l4h6MGNDHxZNbj BMiRwr9Ga9v0g== From: "Vlastimil Babka (SUSE)" Date: Wed, 15 Jul 2026 12:10:52 +0200 Subject: [PATCH RFC 12/12] 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: <20260715-b4-objext_split-v1-12-9a49c4ccf4c3@kernel.org> References: <20260715-b4-objext_split-v1-0-9a49c4ccf4c3@kernel.org> In-Reply-To: <20260715-b4-objext_split-v1-0-9a49c4ccf4c3@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 | 12 ++++++++++-- mm/slub.c | 3 +++ 3 files changed, 19 insertions(+), 2 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 6303a2b1a9d0..09659722ec85 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_objcgp(obj_ext); @@ -3581,6 +3584,9 @@ 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 948d075cdbef..072cc2506756 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -622,7 +622,15 @@ static inline size_t static_obj_ext_size(void) static inline size_t slab_obj_ext_size(struct slab *slab) { - return static_obj_ext_size(); + 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 @@ -741,7 +749,7 @@ static inline struct obj_cgroup **slab_obj_ext_objcgp(struct slabobj_ext *obj_ex 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 771d73abacb6..09c4931e5435 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2503,6 +2503,9 @@ 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