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 D92AE3AC0D7; Tue, 26 May 2026 05:44:25 +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=1779774266; cv=none; b=S5F9/EMBTeeMyGuIrrJsGBAiEcIA0+9cih68OCBic0GDhzr6PihAEqrEgIr3muoZcs0h7lhJPebYwhGqlz5m170uhC/8ofIG8Zx380auLl0O/8/eItcQone+T3LkxpcFpMOr1f+G1WRHxYqHdq5SfBTccZIQX9isLeHHSD7xi0I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779774266; c=relaxed/simple; bh=6wqgINfsAdR/z7Yl9b3319gY8kjh/uhm+d3m9EjO+kM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=qdyYBOQyGTnq+WxifRVDJPQKZ+hPsUbv0QQiPvoiPHqyWwmPS9U5bi4+DafLPcsyVzHoDnl/RS0G+Rrdw3uajY88C3V9lJmI00ZPmLA/r8EfFh/0TSoIuT7W3YnS4MLt+foEn15ioJtlieg5U8ZYqadMRDb2eb4jE9+tcBTihqg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=nq04UDJh; 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="nq04UDJh" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 28A101F000E9; Tue, 26 May 2026 05:44:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1779774265; bh=3LOeGxgwB1u3VB8Q18Mmd6WSv8GQDWdxyl8YN5KUzh0=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=nq04UDJhGT7I6ZyKgOKhlOU2vI2Gz8n1X0V80IftTAF9gZBfmk28aGNvgAY1ORehc ruai1IVtmqjSfo44/I6fbdYOVqpxvL+1929F5bp1/pH5HYB3dOqwRW7YWBlpTOVjyt 8TliOeKRU+O/WTWqVT4z5hc+y7AyMshF35rVTpH0x+ZpyE5a+suLLpewyvEifFzACp rU8QFbyPKrBaaJcCPQlDWVc9MeKngzVq7hNWy8dgW850yXHMVCY52QGHPMnYmbY/ih 0Sl+VdkCyjtMfLnrQGD9BsQGy5/Oy22bFsOQAeIubfXGS4Okcc5wblSAzY9djw9tE9 J/epgrSL3JDSg== Message-ID: Date: Tue, 26 May 2026 14:44:21 +0900 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: [PATCH v3 4/4] memcg: multi objcg charge support To: Shakeel Butt , Andrew Morton Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Qi Zheng , Alexandre Ghiti , Joshua Hahn , David Laight , Meta kernel team , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel test robot References: <20260526033931.1760588-1-shakeel.butt@linux.dev> <20260526033931.1760588-5-shakeel.butt@linux.dev> Content-Language: en-US From: Harry Yoo In-Reply-To: <20260526033931.1760588-5-shakeel.butt@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 5/26/26 12:39 PM, Shakeel Butt wrote: > Commit 01b9da291c49 ("mm: memcontrol: convert objcg to be per-memcg > per-node type") split a memcg's single obj_cgroup into one per NUMA > node so that reparenting LRU folios can take per-node lru locks. As a > side effect, the per-CPU obj_stock_pcp -- which caches exactly one > cached_objcg -- thrashes on workloads where threads of the same memcg > run on different NUMA nodes. The kernel test robot reported a 67.7% > regression on stress-ng.switch.ops_per_sec from this pattern. > > Mirror the multi-slot pattern already used by memcg_stock_pcp: turn > nr_bytes and cached_objcg into NR_OBJ_STOCK-element arrays, scan all > slots on consume/refill/account, prefer empty slots when inserting, > and evict a random slot only when full. With multiple slots a CPU can > hold the per-node objcg variants of one memcg plus a few siblings > without ever forcing a drain. nit: evict a random slot -> evict a slot round-robin > A single int8_t index records which slot the cached slab stats belong > to; the stats are flushed on slot or pgdat change. With NR_OBJ_STOCK > = 5 the layout (verified with pahole) is: > > offset 0 : lock(1) + index(1) + node_id(2) + slab stats(4) = 8B > offset 8 : nr_bytes[5] = 10B > offset 18 : padding = 6B > offset 24 : cached[5] = 40B > offset 64 : (line 2) work_struct + flags (cold) > > so consume_obj_stock, refill_obj_stock and the slab account path each > touch exactly one 64-byte cache line on non-debug 64-bit builds. > > Reported-by: kernel test robot > Closes: https://lore.kernel.org/oe-lkp/202605121641.b6a60cb0-lkp@intel.com > Fixes: 01b9da291c49 ("mm: memcontrol: convert objcg to be per-memcg per-node type") > Tested-by: kernel test robot > Signed-off-by: Shakeel Butt > --- Looks good to me, Reviewed-by: Harry Yoo (Oracle) -- Cheers, Harry / Hyeonggon