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 7E9FC367B86; Mon, 27 Jul 2026 12:54:08 +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=1785156849; cv=none; b=DZycWNw4FYiqdjt6XpO04S4k83ADFk3nlfLFnPfaS/5HzHo30cWEHtz0x46RMJUBHCT4L7FZHTwk0p+GsVnHLLf2mACcQM9/6z425O9hwZcR8gw6lQVY8Bm3pAcIoA6RJjOGRQ3FpJ7kyH8/1mlaMq9hr63Cp9w2pSZGsj2GeuE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785156849; c=relaxed/simple; bh=voXlQsdNnQ7Hv2FMR6To+pkYh4z0pNUG74KxFNkT5wU=; h=From:Subject:Date:Message-Id:MIME-Version:Content-Type:To:Cc; b=W5JFQL/trYRSt1heLaKebfV7fNMcCuXQQXAcer5nGJW75nXMzp8Cv+EoeLkVMa3jBgc3I5jINzhmJKS5qtRAUy0fPH5E37uQ2Vb6ksb0hj6ZVP9Q6NnLvgrOpz+tk75kfGegMZALuQQIpNPx+KpFJHiDajrzFEpyVm+rZ4NIl+Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ls8MpmHA; 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="ls8MpmHA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 548CD1F00A3A; Mon, 27 Jul 2026 12:54:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785156848; bh=y9olFz4RC6C1U7zYxBQoZxiDRdf5OldBtN1enHJw5Kc=; h=From:Subject:Date:To:Cc; b=ls8MpmHAhsKvwNvNa/Q/2fVB4LTcEBCBfbTZKm2UUX2BO7+/BUTL7sNffmT1Ve+nY aeBznRVglidHOLdmOzrmE+NWF3ZmFlV3K14BdaSDfDCGk4lKpIYtOYnK+TlI6+QcU2 mB8hFL5MLoflRqpTyupnU5a/1A18lQ/pgZZKbbZQffF04SSTqxmC7KTf7wA4piH2dp 9Ml+7RJN7lFQex4koS3qSgxEW/NPz8yzLUOcSFy1QqW2XszJCM8nnanHdeL3o/ROdx PKYNROUsWzXLiUVGTiZ8rFzf9RYVl6zvQwhXYwB6xUk4sOXeEDFiRYgti7leuPhbNT XaxZHjsBTBsqg== From: "Vlastimil Babka (SUSE)" Subject: [PATCH v3 00/13] mm/slab, alloc_tag: reduce obj_ext memory waste Date: Mon, 27 Jul 2026 14:53:54 +0200 Message-Id: <20260727-b4-objext_split-v3-0-c29ef0f1f257@kernel.org> 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 X-B4-Tracking: v=1; b=H4sIAOJUZ2oC/2XN0QqCMBgF4FeJXbeYv1Ozq94jIub2qytxsq1hi O/eNILCywPnfGciDq1GR067iVgM2mnTx5Dud0S2om+QahUzAQY5KxJOK05NdcfR39zQaU+VOAK HHLJCZSSuBou1Hlfxcv1k94wD6RdmabTaeWNf62VIlt5XzzZ6SCijpeCl5FLWXKbnB9oeu4OxD Vn4AD8AsC0AEYBaFDKvc6Yq/APmeX4D9bEfMgIBAAA= X-Change-ID: 20260714-b4-objext_split-da82426257d5 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 The recent fixes for objext array handling inspired me to look into this finally. It's been bothering me that the memory usage of struct slabobj_ext depend only on config options and not whether the fields are actually used. So with both CONFIG_MEMCG=y and CONFIG_MEM_ALLOC_PROFILING=y there is always objcg field and codetag_ref field. And thus: 1) Having memory allocation profiling config-enabled but not boot-enabled means wasted memory on unused codetag_refs. This makes it less suitable for a general distro config and the page allocator side doesn't suffer from this, only slab and percpu. 2) Complementary, with memory allocation profiling enabled, there are caches/slabs that don't need the objcg field, so memory is wasted on those. This series should solve the point 1) fully for slab, pcpuobj_ext handling can be perhaps improved similarly, haven't looked into that. For 2) it avoids allocating objcg fields for KMALLOC_NORMAL and KMALLOC_NO_OBJ_EXT caches where we know they are not necessary because kmalloc() with __GFP_ACCOUNT will pick a KMALLOC_CGROUP type (except with SLUB_TINY). The named kmem_caches are tricky. They can be created with SLAB_ACCOUNT and then we know objcg fields are always needed. But also they can be created without SLAB_ACCOUNT and then some allocations have __GFP_ACCOUNT and some not and we don't know that in advance. This series introduces a SLAB_MAY_ACCOUNT flag that's currently internal only and is applied to all caches (unless kmem accounting is disabled) except KMALLOC_NORMAL (unless that aliases KMALLOC_RECLAIM) and KMALLOC_NO_OBJ_EXT. As a followup we can make SLAB_MAY_ACCOUNT explicit and add it to to caches where we know __GFP_ACCOUNT is used. Then we could only honour __GFP_ACCOUNT for those, while warning for an unexpected usage elsewhere. Based on slab/for-next-fixes Git branch: https://git.kernel.org/pub/scm/linux/kernel/git/vbabka/linux.git/log/?h=b4/objext_split Moderately tested, nothing seems to crash. To check for regressions, I forward-ported a microbenchmark hacked into slub_kunit that was used to evaluate sheaves. You can find it here along with the series: https://git.kernel.org/pub/scm/linux/kernel/git/vbabka/linux.git/log/?h=objext_split-v3-bench Tried 3 scenarios, MEMCG and KFENCE were always enabled: - CONFIG_MEM_ALLOC_PROFILING=n - CONFIG_MEM_ALLOC_PROFILING=y but _ENABLED_BY_DEFAULT=n - same but booted with sysctl.vm.mem_profiling=1 The results are quite noisy, but no regression was apparent, except perhaps few percents for the last case. I don't expect it will be visible in any real workloads. Signed-off-by: Vlastimil Babka (SUSE) --- Changes in v3: - Review tags from Harry, Hao, Suren - thanks! - Patch "skip handle_failed_objexts_alloc() with profiling disabled" removed, the check is done as part of "reduce slabobj_ext memory with allocation profiling disabled" using slab_obj_ext_has_codetag() (Harry). - Move kfence checks earlier in mark_obj_codetag_empty() in Patch 1 (Harry). - Remove SLAB_MAY_ACCOUNT also for KMALLOC_NO_OBJ_EXT caches and more precise description in Patch 11 (Hao) - Add a new cleanup patch 13 that removes also memcg accounting from kfence allocations, as suggested by Harry. - Link to v2: https://patch.msgid.link/20260720-b4-objext_split-v2-0-2fa7c6f60dbe@kernel.org Changes in v2: - Apply Suren's R-b:, thanks! - Expanded explanation about no longer accounting KFENCE objects (Suren) - Also skip them in in mark_obj_codetag_empty() (sashiko) - Update slab_obj_ext() comments (sashiko) - Separate slab_obj_ext_objcg() and slab_obj_ext_set_objcg() (Suren) - Add SLAB_MAY_ACCOUNT internal flag instead of relying on is_kmalloc_normal(); also handle mem_cgroup_kmem_disabled() - Also fix the SLUB_TINY kmalloc aliasing handling, per Harry. - Link to v1: https://patch.msgid.link/20260715-b4-objext_split-v1-0-9a49c4ccf4c3@kernel.org --- Vlastimil Babka (SUSE) (13): mm/slab: skip kfence objects in allocation profiling mm/slab: remove objs_per_slab() mm: move struct slabobj_ext to mm/slab.h mm/slab: make slab_obj_ext() determine object index mm/slab: abstract slabobj_ext.objcg access mm/slab: abstract slabobj_ext.ref access mm/slab: replace slab.stride with obj_exts_in_object mm/slab: change struct slabobj_ext to a union mm/slab: introduce slab_obj_ext_has_codetag() mm/slab: reduce slabobj_ext memory with allocation profiling disabled mm/slab: add cache_ and slab_needs_objcg() helpers mm/slab: stop allocating objcg pointers when unnecessary mm/slab, kfence, memcg: completely remove obj_ext for kfence objects Documentation/mm/allocation-profiling.rst | 7 ++ include/linux/memcontrol.h | 13 -- include/linux/slab.h | 3 + mm/kfence/core.c | 12 -- mm/kfence/kfence.h | 3 - mm/kfence/kfence_test.c | 2 +- mm/memcontrol.c | 40 ++++--- mm/slab.h | 189 ++++++++++++++++++++++++------ mm/slab_common.c | 26 +++- mm/slub.c | 184 ++++++++++++++++++----------- 10 files changed, 325 insertions(+), 154 deletions(-) --- base-commit: 5ff172f6c94d282d83cb88bdfec5f647ad9c6105 change-id: 20260714-b4-objext_split-da82426257d5