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 43D9835F8B9; Thu, 16 Jul 2026 09:11:13 +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=1784193082; cv=none; b=pSohBush+9T67N/t8EhXG1/z3kmjiIugEX7Hny4JvjtDmG5CAe+jBF104imJ4rnjeAkioAbV8AdTKzBokdvZVKNPiVmfwiPOT0fls6Ex7bpOH/XWxxl4RwLa0+hn7HVij6SiMovneG2G9aTgM68h/pYDk3mXQG6MAQ/Tc7NQL/4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784193082; c=relaxed/simple; bh=KPce9QFMgAIwe+cwCpgtpgfsU9rtNqF4p5MVTIBLk84=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=WWVYLcFFXMBnp6aWR+wTtrcTdnyyHBK+R0IU7DstKYb07pAsm6JZHM8bMJ5UWySThBSbovDRYDEy4b7xCT/IMUxH4urJTDEqyszBQdZkhab2aMu4F1jUkTDmh/IAEnmKlEtuIDr/ct1I00cwYDNaioEo111myA0HimW8lyJ+SXE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Z2vbq3wO; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Z2vbq3wO" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 45C981F000E9; Thu, 16 Jul 2026 09:11:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784193071; bh=iKN5NO81HJ06ZzzJkfJP7JqXMoZORuMoTwUI7uq6cgs=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Z2vbq3wOpl76S0pNL0BrryzAjWr95MujoIU0p1D4TZj1lBt/ZIgS18pgjo/Z5r/jV wTpZvwRRRrReEfLqcNc+TMBxpomB+f7LPVQuAi/mzYUmVg5NuiwcSo14a5Z0ZVF9aC CkG2S1iU/K3K8q1xWNrudiqqdEgb7KCiTkK4jce5pLs0IQtn5s6XULuzZ0jhdnlks7 WgzMFWZOy3kzi6l6gSAHAYHHFGoQ4jAGglmqi3ABDTBVHDiG4FaGlvHFA5L4tUFMUt 0ehqga7FYirHu/3EtF3fXQ5UhHrbWXs9kOYAGwXUy+1lpJw4+cjDzWPkC6z0g/3+rf 5dKtDD8PK04vA== Message-ID: Date: Thu, 16 Jul 2026 11:11:06 +0200 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 01/12] mm/slab: skip kfence objects in allocation profiling Content-Language: en-US To: Suren Baghdasaryan Cc: Harry Yoo , Hao Li , 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 References: <20260715-b4-objext_split-v1-0-9a49c4ccf4c3@kernel.org> <20260715-b4-objext_split-v1-1-9a49c4ccf4c3@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 7/15/26 18:02, Suren Baghdasaryan wrote: > On Wed, Jul 15, 2026 at 3:10 AM Vlastimil Babka (SUSE) > wrote: >> >> struct kfence_metadata only has obj_exts with CONFIG_MEMCG. > > I don't quite understand this statement. obj_exts are allocated when > either CONFIG_MEMCG or CONFIG_MEM_ALLOC_PROFILING is enabled. See in mm/kfence/kfence.h struct kfence_metadata { ... #ifdef CONFIG_MEMCG struct slabobj_ext obj_exts; #endif ... then in mm/kfence/core.c kfence_init_pool() #ifdef CONFIG_MEMCG struct slab *slab = page_slab(page); slab->obj_exts = (unsigned long)&kfence_metadata_init[i / 2 - 1].obj_exts | MEMCG_DATA_OBJEXTS; #endif So the slab kfence fakes only has this pre-inited obj_exts with CONFIG_MEMCG. What happens if we run memalloc profiling without MEMCG and this fake slab doesn't have a pre-assigned obj_exts? I guess __alloc_tagging_slab_alloc_hook() will allocate it via prepare_slab_obj_exts_hook(). But it's something that was done consciously and probably just accidentally works. >> If it's >> enabled, it does also work for allocation profiling, but there's little >> value recording tags for KFENCE objects. > > Unless we are leaking them, right? Well if there are leaks in a particular callsite, we should see that from all the allocations that don't end up in kfence (as kfence allocations are rare). So we are very unlikely to miss a leak due to this. >> Furthermore it would complicate >> the upcoming changes, so just skip them in the slab hooks. > > Ok, I can understand that. If we do this, we should document that > kfence objects are no longer tracked. > >> >> Signed-off-by: Vlastimil Babka (SUSE) >> --- >> mm/slub.c | 6 ++++++ >> 1 file changed, 6 insertions(+) >> >> diff --git a/mm/slub.c b/mm/slub.c >> index 0337e60db5ac..a4be70d080fb 100644 >> --- a/mm/slub.c >> +++ b/mm/slub.c >> @@ -2352,6 +2352,9 @@ __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 +2402,9 @@ __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 >>