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 40EFC440620 for ; Tue, 15 Sep 2026 07:10:26 +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=1789456227; cv=none; b=mU+aaYDIF2igSIz1NQtQ+CGvjZLshI4bOPG45Jyu2lMXnw0a2xl2Q6A2t9PCO55ndDAfncYDCTDn6Lx4Yi2843p6a/ZS7jmqolbM4B3rnsG5J2xMEc12t9HkNHXXtTBnjv82zvDhNb9G7/7bno++P7sMimp3CAcHIEoW3BYVw2U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789456227; c=relaxed/simple; bh=d0Q9BrXQeEl33vqAz13JgA5Tz08bFat37n7Ps7zdrb4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=eKj6Lr93qa6xU3JyAmFiix4RyvkDPBZBDvAflKy7ijOvELyNnBYDJH6bwOsIIwmpJ1Gi3GqGXiYfTs9P5UkW+Gy0Kt8eabiR04DqoJGiGdhmDVcMiaLDjEh9itVoiqkiybkyGtUoBohMC/G0hCLtnpk26veqTub2rDRM/eq1Umk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=O05SGGAd; 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="O05SGGAd" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1E9DB1F000FF; Tue, 15 Sep 2026 07:10:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789456225; bh=oKxcff3RknMtu3nP96OKoAusCWTbG23nN8Jci2XLj7M=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=O05SGGAdRPGrz0Iz+7XgwlSFs3F5RnNc0orTk5KU9yz8aeD27Z+fCAQ3JX0fHfAEj xCod+mWvLIGO/opeBlR1JATMb1O+8IRDeeSegYbMSJR+L9p5b2Ub+H2SkHHpUfRdLI qy6BtR30pEznfw5G2Iuf6kFVI7MNCf+iTXB84EaRmILGvGIc5FPXdkP9Ff8ytneID7 gIFmvbA+UcB/J23fjfmlJoNt24rtTwQzOs/B4UV5CiExvTA4rmgoVawucc8weY5wUN Hpb6skjv+czEk0J2VNgwAc9cIVAlFId7X9MaNUxsJqVfimJLnn0UL4iyyFxOuckQTi 5VOJUhZcIujVg== Message-ID: <4d9ebf64-e3b4-4b6c-9576-e8be59193f80@kernel.org> Date: Tue, 15 Sep 2026 09:10:22 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 0/2] mm/slub: reduce list_lock contention with slab parking Content-Language: en-US To: Hao Li Cc: harry@kernel.org, akpm@linux-foundation.org, cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Pedro Falcato References: <20260824122004.3652-1-hao.li@linux.dev> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/11/26 13:24, Hao Li wrote: > On Mon, Sep 07, 2026 at 03:44:08PM +0200, Vlastimil Babka (SUSE) wrote: >> On 8/24/26 14:19, Hao Li wrote: >> > >> > Detailed data >> > ------------- >> > >> > metric before after delta change >> > ========================================================================================== >> > alloc_fastpath 155,417 168,534 13,117 +8.44% >> > alloc_slab 55,679,646 26,702,510 -28,977,136 -52.04% >> >> It's interesting that this is reduced so much. Is it because parked slabs >> cause more slabs to stay around for reuse, despite they are unparked >> immediately when trying to allocate/refill? That seems odd? > > Yeah, it does look counter-intuitive at first glance. My understanding is that > the parking mechanism helps by bypassing the partial list spinlock, allowing > partial slabs to be parked onto the llist locklessly at any point. Because of > this, the refill path gets to see and reuse more partial slabs instead of > having to allocate fresh ones so frequently. Hmm that's an interesting effect, surprisingly large if true. Because the slabs we'd be parking are transitioning from full, there would be most often just a single free object to reuse? >> >> > alloc_slowpath 0 0 0 +0.00% >> > barn_get 2,715 2,771 56 +2.06% >> > barn_get_fail 2 0 -2 -100.00% >> > barn_put 2,715 2,770 55 +2.03% >> > barn_put_fail 1,370,488,457 1,668,257,974 297,769,517 +21.73% >> > cmpxchg_double_fail 3,827,935 549,427 -3,278,508 -85.65% >> > free_add_partial 1,684,340,964 2,161,921,625 477,580,661 +28.35% >> > free_fastpath 31,766 32,979 1,213 +3.82% >> > free_rcu_sheaf 43,855,689,417 53,384,314,553 9,528,625,136 +21.73% >> >> This metric (and others with similar numbers) should not be affected by the >> change. Does it mean the benchmark has a fixed time to run, but manages to >> do more work in that time thanks to the increased throughput? > > Exactly! In fact, the increase in free_rcu_sheaf matches the throughput gain > almost 1:1. A ~21% increase in throughput naturally translates to ~21% more object > allocations and frees. Ack!