From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 BBF9E19FA93; Wed, 25 Feb 2026 11:29:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772018970; cv=none; b=buntlCRSBf5kBG5hCCudSL95IdbZqDEm6jdqqZ/V0EQSKQa1ZDOlxpJMVDhtZwT/ZsaWIPvqqB4HCOmOkpR0STi5VrBRPByoD3f2lTZT44yTnG2maMrFuU9QKmIsq/4Cm/1EkHkXLmZZo8mRYOUXeB8Co16hY2dP/JIPJOUNSK8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772018970; c=relaxed/simple; bh=ZoMjdr0T6OM95kTpTHlHC/FoYXWZ4T8BYxxD5K3H2Qo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Ni0prRihUoTivoR0lgVdzSlxqtWEGdBKYm4ky/CSKASWO7Ppuvs6SVmJT8+/04Hcae1UkE3trCu8H/SDpJMZyksiII2UPoFb5z394e8RcQSv/YRGR9pV8QzCFG6MNSkm/RrgMaA64DE3/Jb1LPNuXbNM54QAjZD9AtIf1RW2zME= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=PWpiXD1v; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="PWpiXD1v" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B3DA3C116D0; Wed, 25 Feb 2026 11:29:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772018970; bh=ZoMjdr0T6OM95kTpTHlHC/FoYXWZ4T8BYxxD5K3H2Qo=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=PWpiXD1vPXYvxvOheOYqV1U5YoimDIoPoi+fFNBTpYbOOXaZz5UfXmpwYuZG158E8 40GGsVEDIH7wfNfv0tFBHRGOMHZBRK4elGleYsKFoaJMG5qjfuSYF0yzqkVV8/7zBt 2wTnop450r3CkoMM58GF+dcSJ3/+WHYWJw5tmKOubTtfrHoFuXZ2k1ttVqdYOMPSDi oi7Tsn+TURZe/oRzDmMdFCVytlfba2ab6DDYgXZRbvYgRVPFyDKXRCzwF1Dg30+EGE VFocWPZ7GYHPLjDZZB7d4Gm0IkS7klHUd2KkNL+eJiyiveZ0ChhDoq2Mbs7imb5mL/ JTad5V2+X7U5A== Message-ID: Date: Wed, 25 Feb 2026 12:29:26 +0100 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [Regression] mm:slab/sheaves: severe performance regression in cross-CPU slab allocation Content-Language: en-US To: Ming Lei Cc: Vlastimil Babka , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, Harry Yoo , Hao Li , Christoph Hellwig References: <5cf75a95-4bb9-48e5-af94-ef8ec02dcd4d@suse.cz> <724310c2-46a2-4410-8a5d-c69dcc8de35d@kernel.org> From: "Vlastimil Babka (SUSE)" In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 2/25/26 10:31, Ming Lei wrote: > Hi Vlastimil, > > On Wed, Feb 25, 2026 at 09:45:03AM +0100, Vlastimil Babka (SUSE) wrote: >> On 2/24/26 21:27, Vlastimil Babka wrote: >> > >> > It made sense to me not to refill sheaves when we can't reclaim, but I >> > didn't anticipate this interaction with mempools. We could change them >> > but there might be others using a similar pattern. Maybe it would be for >> > the best to just drop that heuristic from __pcs_replace_empty_main() >> > (but carefully as some deadlock avoidance depends on it, we might need >> > to e.g. replace it with gfpflags_allow_spinning()). I'll send a patch >> > tomorrow to test this theory, unless someone beats me to it (feel free to). >> Could you try this then, please? Thanks! > > Thanks for working on this issue! > > Unfortunately the patch doesn't make a difference on IOPS in the perf test, > follows the collected perf profile on linus tree(basically 7.0-rc1 with your patch): Hm that's weird, still the slowpath is prominent in your profile. I followed your reproducer instructions, although only with a small virtme-ng based setup. What's the output of "numactl -H" on yours, btw? Anyway what I saw is my patch raised the IOPS substantially, and with CONFIG_SLUB_STATS=y enabled I could see that /sys/kernel/slab/bio-248/alloc_slowpath had substantial values before the patch and zero afterwards. Maybe if you could also enable CONFIG_SLUB_STATS=y and see in which cache(s) there's significant alloc_slowpath even after the patch, it could help. Thanks! > ``` > 04cb971e2d28 (HEAD -> master) mm:slab/sheaves: severe performance regression in cross-CPU slab allocation > a5a9cf3f020f mm: fix NULL NODE_DATA dereference for memoryless nodes on boot > 7dff99b35460 (origin/master) Remove WARN_ALL_UNSEEDED_RANDOM kernel config option > 551d44200152 default_gfp(): avoid using the "newfangled" __VA_OPT__ trick > 6de23f81a5e0 (tag: v7.0-rc1) Linux 7.0-rc1 > ``` > > + 49.03% 2.00% io_uring [kernel.kallsyms] [k] __blkdev_direct_IO_async > - 38.66% 1.16% io_uring [kernel.kallsyms] [k] bio_alloc_bioset > - 37.51% bio_alloc_bioset > - 34.98% mempool_alloc_noprof > - 34.87% kmem_cache_alloc_noprof > - 33.82% ___slab_alloc > - 30.25% get_from_any_partial > - 29.59% get_from_partial_node > - 28.42% __raw_spin_lock_irqsave > native_queued_spin_lock_slowpath > + 2.16% allocate_slab > + 0.60% alloc_from_new_slab > 0.51% __pcs_replace_empty_main > 1.58% bio_associate_blkg > + 1.16% submitter_uring_fn > + 35.16% 0.30% io_uring [kernel.kallsyms] [k] kmem_cache_alloc_noprof > + 35.13% 0.12% io_uring [kernel.kallsyms] [k] mempool_alloc_noprof > > > Thanks, > Ming >