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 2F4CF3CCFC4; Fri, 24 Jul 2026 15:58:39 +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=1784908721; cv=none; b=IB+rTgqIFiwEYfPRh/EZCqypAz89f6/LrLm+FRkC5Tk1IeXqH3eJAeCuN4u3QNowpB0k/Bu7Z4mScwVDbz/4MrmwGw8A7LjXDraSch/o5vEAjPi2X/Q8VEoAhpYlhoNbBewIpmqwcLS0/0to8F8UVJRAT04EdYLdyHhuccqkUYY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784908721; c=relaxed/simple; bh=FFhgyd20eZJcVmzCjIbz4H6kvXz4YIdmMPHxPc8SLTo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=sgALUyQypUwRAxmrUvZ2RGHOLBsWEtZ8gsHmh23rOMBi1y2IBR+sD9qpnHudtlLS325jzSYRguj4oakZR0XUmRfjUsm0MozA6ummqloUVoBKLHtaIIB8pe4eMuVsSNsPRw0SOzjfvq3qYhJrs+73DfgrDLUA3QLAd2QUXZKaeKQ= ARC-Authentication-Results:i=1; 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charset=UTF-8 Content-Transfer-Encoding: 7bit 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. 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 >> >