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 91B092F5A12; Fri, 31 Jul 2026 13:49:59 +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=1785505800; cv=none; b=jz8msEcCWnLwwgSmmQbCJ0uFIMtRmo/HO66keQY4nHCrNg6G6kSxRAWHyxjic/UeUgOfkaYFet744RZIzqmnQ6xwxPgY9+DRuOqtZFfNEQTh12YBbv8Hcl1zoyFLz6Rpo/YE7IX/azCQRL9aqgszYQ4Il09aR174i4aAZrV+4cM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785505800; c=relaxed/simple; bh=iBzAO5FSJOJM0/Hs8vWNkgzEQGma4FdVaPnPk1NNgmg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=rJffb5ctxowp2Aq4XH05LFTp2Pn1ZT9v7l4f1nYwM+D20yUw603WH3eM5zeca7Ffi2PcdUGz/IOLAovgZM4KFv7qP6FQre3laOt4FiKOjKZ1qMRKGtdKA2jodt8B8XCYMLxv1pUDsGt2U25LK+deSD4kgWzMGN7bBfVEnG6Dxek= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GaXFjw9u; 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="GaXFjw9u" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 88EF41F000E9; Fri, 31 Jul 2026 13:49:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785505799; bh=E6/53IoTaITFwF6OJqnQibU8ofhN9Lsow6iDpep0Xps=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=GaXFjw9ui0agGo1svAJcB/SttjHf5dRf1X34eOINiDbZ9wl3erajDcnoFQGY4AkF+ ZdOt1sWOKikj9vjtnoJFEScSFQrHDdIJljctwT2uK6JqRFDQ5SgtSAyb1h74SLnYgc emA9164rFG2eP6Pccs7d5Qk4zL5njRqH1EK5B+wB4NoCNxg0GYJsNkxSojfarvcH8X 52YQjalKaamshJOOjaKDCCO+f5BItXxNrcBbqJlYeGefIGhNiM0C4p6+qV56WkZpx2 YL/IM9zcAVhQMileoGITOSlOYx15gQQUc3mqO/0UkbnoY9RpWa01O/sJHmv5fkaNO3 p/MK+xBS4aMRg== Message-ID: Date: Fri, 31 Jul 2026 15:49:54 +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 v3 01/13] mm/slab: skip kfence objects in allocation profiling Content-Language: en-US To: Hao Li 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 References: <20260727-b4-objext_split-v3-0-c29ef0f1f257@kernel.org> <20260727-b4-objext_split-v3-1-c29ef0f1f257@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/30/26 13:16, Hao Li wrote: > On Mon, Jul 27, 2026 at 02:53:55PM +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 | 9 +++++++++ >> 2 files changed, 16 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. > > should this be 'allocation profiling is skipped' instead? The document uses the word "accounting" when it comes to individual allocations, so this fits. > Otherwise, looks good to me. > Reviewed-by: Hao Li Thanks!