From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-189.mta0.migadu.com (out-189.mta0.migadu.com [91.218.175.189]) (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 A8BCF3BE15E; Mon, 27 Jul 2026 06:21:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.189 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785133288; cv=none; b=oxsDVOt96zAfY7pSN8Z5zUfbceLEK0VJvN5RyQDIE7dLnAdphaiK+rXvLT+wNufzdBTna7z21aWb8ZE72YOOAfyuZIu8XEaObSsp5j7H4mkdiPr0nZO6jECzAxcROYqLWbiEsHiaqH4pbPTU6+5o+E8eQyCsRHwdIg2jjbRKc9I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785133288; c=relaxed/simple; bh=xzTt2z59QC8Q2Nk5Pd1XFFGw2YHnRkVkQPpnu40JYto=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=kN166Ru99pawKenPM6ZgdTLcRrWV7pKq880Y/GENJfGV2AJIgbikY49LynHmPBTr8CL/8q0Znr90ukPnX8FdAijbR/TVvulDsnHq5J2pKSzKMnhpreFXH2ljg0XLFraK7WVCBUsa5BQABZopPharvXMfL1PO+iiVmyITBGKAbw4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=paWi0RpD; arc=none smtp.client-ip=91.218.175.189 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="paWi0RpD" 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> 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=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT 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