From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-172.mta1.migadu.com (out-172.mta1.migadu.com [95.215.58.172]) (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 EEEC3CA52 for ; Wed, 22 Jul 2026 12:49:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784724542; cv=none; b=JX+SOWQSSK/qCtQbRgFgO3s5x3OZSI4u4OMnS0y+P9lsfYi1LopIsaMfVkF7pi+qQCYp8TNioKIoY4Cd93wr0VB5qoZpO2oxhWzrXygTzDiBXY172Z6oqr9ZsWo77mPL8m3lFoNj+v5lZviSJGfGm2ImC9b7AFoilEKqIxPGs7w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784724542; c=relaxed/simple; bh=Z7GiHQzgOLmmCHoovQUTTYnria8wPNoFHnPJkJUQiMo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=JBHAL+Brh4+j2eR9WHQz4O/oQ7oW3MovTFv5lm4Cc9TNZVwl8fEg3OmsnibMJMUMgBL83zYIrFUmW7kKPb93Y9CqX5gDTC3c8SORHC+TKtOOuBI7oYHNcYmZRksVyf5OTgPuZZLtnwxNQDZ+n2L/fb4aNUI78DpB7LYx6kc/c3Q= 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=tntCcpwE; arc=none smtp.client-ip=95.215.58.172 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="tntCcpwE" Date: Wed, 22 Jul 2026 20:47:39 +0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1784724528; 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=dfnrtyzHcc7q+v7KzgfWL76gnj0hMYo6SrwEr84OSvg=; b=tntCcpwEEhLS/XWXoNqPZperSBZt5F5W/sXXnga+w0LpJtzlyYRmmPtkIVN+6q09sqs/0e MBKLhGzAWfMEScfkDQqN2tzJwcoIJJMaLV/AiGzzB3xoYaQOKEo/ckDrFPJlKrtEDtIl+7 +yyHHnZ8vfdChOnyoYqHc0L9ttrvdyc= 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: cgroups@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: <20260720-b4-objext_split-v2-1-2fa7c6f60dbe@kernel.org> X-Migadu-Flow: FLOW_OUT 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); > > + 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