From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id E29CAC55160 for ; Thu, 30 Jul 2026 11:17:20 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id AC8D56B008A; Thu, 30 Jul 2026 07:17:19 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A79846B0093; Thu, 30 Jul 2026 07:17:19 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 98F596B0095; Thu, 30 Jul 2026 07:17:19 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 786416B008A for ; Thu, 30 Jul 2026 07:17:19 -0400 (EDT) Received: from smtpin10.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 0507E1C12C7 for ; Thu, 30 Jul 2026 11:17:18 +0000 (UTC) X-FDA: 85045191798.10.57DD9A9 Received: from out-181.mta1.migadu.com (out-181.mta1.migadu.com [95.215.58.181]) by imf22.hostedemail.com (Postfix) with ESMTP id CE9E3C0009 for ; Thu, 30 Jul 2026 11:17:16 +0000 (UTC) Authentication-Results: imf22.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=YaPbCgjo; spf=pass (imf22.hostedemail.com: domain of hao.li@linux.dev designates 95.215.58.181 as permitted sender) smtp.mailfrom=hao.li@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1785410237; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=O62DfahAFLdgUNQd+mEROE3kc1IiFSoToX+T1c6EMNs=; b=qWMFNVPgOsMJkQ7f/KYRDAtcnYmsFlr4Q+4DAsTvyjUbVNvvpu6eNwfM+RMjrX9LRdYAoa cI61qZtvLW5DxbwKhuLOJzcwfVFiul0js+PDPE6r59z3m35L5WhaY4dUwKapjwf+Uxuw/I PrCNizvpmcQ3gpRAF31vLZxS7NkH1tg= ARC-Authentication-Results: i=1; imf22.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=YaPbCgjo; spf=pass (imf22.hostedemail.com: domain of hao.li@linux.dev designates 95.215.58.181 as permitted sender) smtp.mailfrom=hao.li@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1785410237; b=ZhWN6+0B3lfO/7vNWexrnipPgOSDumq/NkIWGBjzZP8CSRYR+2Or1idvtCizV+T8vd7Tsi Tt8JpxWZslYyVbaYP9bQw+z68k1O86ajD0dcG4xv5L/WrvC5uSp1R+iu2sxiWiacYX8/4I HM7TMercpc4NBPzdvEh7cT26QxUcNWU= Date: Thu, 30 Jul 2026 19:16:47 +0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1785410234; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=O62DfahAFLdgUNQd+mEROE3kc1IiFSoToX+T1c6EMNs=; b=YaPbCgjoftbhSR29RzI9Advqe32g7LQ+h0mgAHtNfh88j26Di9HQPwtfZ2qZL8RShRsfg+ X9u9qjJROPUyXbjGsv9JAAGTvz08KdUC6F2SlIH/17UBk2C6BLlkTOvFewXBx3wMSD3Rkj jWoAh/y38URdus2BcU5fMHYXHePLsaM= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Hao Li To: "Vlastimil Babka (SUSE)" Cc: Harry Yoo , Suren Baghdasaryan , 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 Subject: Re: [PATCH v3 01/13] mm/slab: skip kfence objects in allocation profiling Message-ID: References: <20260727-b4-objext_split-v3-0-c29ef0f1f257@kernel.org> <20260727-b4-objext_split-v3-1-c29ef0f1f257@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260727-b4-objext_split-v3-1-c29ef0f1f257@kernel.org> X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: CE9E3C0009 X-Rspam-User: X-Stat-Signature: uia8c856irxwcyzgjn3gcicxyfdrjziq X-Rspamd-Server: rspam04 X-HE-Tag: 1785410236-20537 X-HE-Meta: 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 o0bXlEdl 9b1L4CQyLm2Y5E5BAHjqpvH7dtfzeN1p4sCNSTtNwX2iVZsb2WHPB12NLvXVQKELF1IJGBgbVIEg4louwTn2mCgQIFejwOS/xGCay8gpw8diJjAjOaAbVvFQPQJF1ET2IhykWGG6aTSDXo01iIvpiEsh81zoaIvsLeWHGZm+QjOjFa4ktR6wjCZoS4xSWVPolH6QdHOSLOMFyPFpDUxW6xyobbTiSsPC2c63yJJYEWR+4V24= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Jul 27, 2026 at 02:53:55PM +0200, Vlastimil Babka (SUSE) wrote: > struct kfence_metadata only contains struct slabobj_ext with > CONFIG_MEMCG, which is then used for the "fake" slab's obj_exts field. > If CONFIG_MEMCG is enabled, the struct can also end up used for memory > allocation profiling. If CONFIG_MEMCG is disabled but profiling is > enabled, it will end up allocating its obj_exts via > prepare_slab_obj_exts_hook() and assigning them to the fake struct slab. > These will probably then never be freed. > > So things sorta work, but not always in the intended and optimal way. > The upcoming changes to slabobj_ext layout would additionally need a > proper refactoring to keep working. > > However, there's little benefit in accounting KFENCE objects. KFENCE > allocations are rare and there can be only CONFIG_KFENCE_NUM_OBJECTS > (default to 255) outstanding ones at any time. For any callsite > prominent enough in the memory allocation profiling stats, allocations > served from KFENCE will be lost in the noise. > > Thus let's not complicate things and simply stop accounting KFENCE > objects in allocation profiling and skip them in the related slab hooks. > > We also need to skip kfence objects in mark_obj_codetag_empty() in case > a sheaf is allocated from kfence, per earlier sashiko review. > > Signed-off-by: Vlastimil Babka (SUSE) > --- > Documentation/mm/allocation-profiling.rst | 7 +++++++ > mm/slub.c | 9 +++++++++ > 2 files changed, 16 insertions(+) > > diff --git a/Documentation/mm/allocation-profiling.rst b/Documentation/mm/allocation-profiling.rst > index 5389d241176a..d02eb54ee8f2 100644 > --- a/Documentation/mm/allocation-profiling.rst > +++ b/Documentation/mm/allocation-profiling.rst > @@ -112,3 +112,10 @@ break it out by rhashtable type. > > - Then, use the following form for your allocations: > alloc_hooks_tag(ht->your_saved_tag, kmalloc_noprof(...)) > + > +Notes > +===== > + > +- When a slab object is allocated from KFENCE, its accounting is skipped. should this be 'allocation profiling is skipped' instead? Otherwise, looks good to me. Reviewed-by: Hao Li > + KFENCE allocations are rare and limited to a small number, so this omission > + is negligible. > diff --git a/mm/slub.c b/mm/slub.c > index 0337e60db5ac..d702d273253c 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -2067,6 +2067,9 @@ static inline void mark_obj_codetag_empty(const void *obj) > struct slab *obj_slab; > unsigned long slab_exts; > > + if (is_kfence_address(obj)) > + return; > + > obj_slab = virt_to_slab(obj); > slab_exts = slab_obj_exts(obj_slab); > if (slab_exts) { > @@ -2352,6 +2355,9 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags, > if (alloc_flags & SLAB_ALLOC_NO_RECURSE) > return; > > + if (is_kfence_address(object)) > + return; > + > slab = virt_to_slab(object); > obj_exts = prepare_slab_obj_exts_hook(s, slab, flags, alloc_flags, object); > /* > @@ -2399,6 +2405,9 @@ __alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p > for (i = 0; i < objects; i++) { > unsigned int off = obj_to_index(s, slab, p[i]); > > + if (is_kfence_address(p[i])) > + continue; > + > alloc_tag_sub(&slab_obj_ext(slab, obj_exts, off)->ref, s->size); > } > put_slab_obj_exts(obj_exts); > > -- > 2.55.0 > -- Thanks, Hao