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 8AE34C531D0 for ; Mon, 27 Jul 2026 06:21:30 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id EACC26B008C; Mon, 27 Jul 2026 02:21:28 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E5F2C6B0093; Mon, 27 Jul 2026 02:21:28 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D4F886B0095; Mon, 27 Jul 2026 02:21:28 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 9890A6B008C for ; Mon, 27 Jul 2026 02:21:28 -0400 (EDT) Received: from smtpin01.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 1195E1A065F for ; Mon, 27 Jul 2026 06:21:28 +0000 (UTC) X-FDA: 85033559856.01.5B16A7F Received: from out-186.mta0.migadu.com (out-186.mta0.migadu.com [91.218.175.186]) by imf10.hostedemail.com (Postfix) with ESMTP id 012CBC0006 for ; Mon, 27 Jul 2026 06:21:25 +0000 (UTC) Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=paWi0RpD; spf=pass (imf10.hostedemail.com: domain of hao.li@linux.dev designates 91.218.175.186 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=1785133286; 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=/fgIomM+t2T3cQpKKoj4SNC1imJIcl8wBpZBAKlnU9I=; b=GnCH6SOSl1y+m7YjDNGKgj1isReHwxOCvmhCzN4k5MHnaVA+rj7j0bXb7Ed2CvKyYB+6Nw ye4rCmAgiTDsAKRvUTXA1hPgkb4u17FdqX6gIV5zh4t5JjaR4TyLchb7Y5jUvw3/WDiMfg CcGf65LaKRTcVAJ6Yx0E1dofbumIJMM= ARC-Authentication-Results: i=1; imf10.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=paWi0RpD; spf=pass (imf10.hostedemail.com: domain of hao.li@linux.dev designates 91.218.175.186 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=1785133286; b=v+Sx8qVUC/vp+3+e1ygeaZjlITWjWnGc4OAQu0+db5r2OqwcVcrU95yNTXhbj8wiKyUMox 7uwxO/X49teBbnpW4jfmG5CNd+vM6TdY4NYebUs3IGjFKpfOgz7iP6vbAg9jVk6FkDvXAK 7+dMPaDKjx8YNSwCzU02wyhtJzCBY/o= Date: Mon, 27 Jul 2026 14:21:12 +0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1785133284; 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=/fgIomM+t2T3cQpKKoj4SNC1imJIcl8wBpZBAKlnU9I=; b=paWi0RpDJlvEn9JWEzhmuu1dzQj5I0SoPhXg10lFhGyhsZ6JfGv4JgmP//o//Y9g8URFoE ypLyygwDMPj6xYquuYt5ZQLa/sm43KrJLofswsr+LVr4z5ZgWcbmEo1uOIGzwnXldxQbkt 1YeUDEMzwEnyeu74CAbGekuNrK3tDiQ= 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 v2 01/13] mm/slab: skip kfence objects in allocation profiling Message-ID: References: <20260720-b4-objext_split-v2-0-2fa7c6f60dbe@kernel.org> <20260720-b4-objext_split-v2-1-2fa7c6f60dbe@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 012CBC0006 X-Rspam-User: X-Stat-Signature: b6ed8w5oqgf75tsniffh978hoheker7j X-Rspamd-Server: rspam04 X-HE-Tag: 1785133285-764827 X-HE-Meta: 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 EhZ9BSTb Mrsm3REiWvLwDs3F77HZFATcnhvkDZRx5i9bVb/+xG04YeHWLAR4YmnufRB+gUYWr1VGePp8YgBekP89eh7LcUc/Ll9C8n25pyI3eCrLO9YRN60BrT8XYBpeBWDEgpgVgMsKBkWJyk3lmI5H6N8ntkNOKn0thYngkxBT00xgUOFfU4pMYZzMDeWz6qtaPh0LkNTA77Y46MoXAB8C4H2cgWwJb3qzl0HKLrN0JWgGp1aeVhOg= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Jul 24, 2026 at 05:58:36PM +0200, Vlastimil Babka (SUSE) wrote: > On 7/22/26 14:47, Hao Li wrote: > > On Mon, Jul 20, 2026 at 04:16:15PM +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 | 11 +++++++++++ > >> 2 files changed, 18 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. > >> + 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..76acb78f2655 100644 > >> --- a/mm/slub.c > >> +++ b/mm/slub.c > >> @@ -2076,6 +2076,11 @@ static inline void mark_obj_codetag_empty(const void *obj) > >> struct slabobj_ext *ext = slab_obj_ext(obj_slab, > >> slab_exts, offs); > >> > >> + if (is_kfence_address(obj)) { > >> + put_slab_obj_exts(slab_exts); > >> + return; > >> + } > >> + > >> if (unlikely(is_codetag_empty(&ext->ref))) { > >> put_slab_obj_exts(slab_exts); > >> return; > >> @@ -2352,6 +2357,9 @@ __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 +2407,9 @@ __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]); > > > > I noticed obj_to_index also does the `if (is_kfence_address(obj))` check, so > > maybe we could use: > > > > if (is_kfence_address(p[i])) > > continue; > > off = __obj_to_index(cache, slab_address(slab), obj); > > Hm it would work, but go away after patch 5/13 anyway, so will leave as is. make sense! > Thanks! > > >> > >> + 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