From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from dggsgout12.his.huawei.com (dggsgout12.his.huawei.com [45.249.212.56]) (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 86612330661 for ; Tue, 6 Jan 2026 13:27:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.56 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767706072; cv=none; b=K0PjMe+qtQL8tJQF7+1eTQY3x1X5O3rFtlOQKua+BQbchGTs9P5812rh14P05jbmoyiYUMYmGYQ/poPfaMI1njujDUGag3LDuYg3gUdOvxue9mpoORY4OY3/dLVI4AnHhgZTgeAgsTnpAtOjDOX/ymRJwzmuswdL8XR70OQdG7Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767706072; c=relaxed/simple; bh=CKHHJLpe7rlM4aJ0x9THVtNxsZ4RUSGSN8fxsYhm/eM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=FdyOQ5hRuYxcRJ2fsfzo16zhEcuGuBeuaEEc/SUrHmTJFpS/9qlmld718K8UqRiHfR6P0FeABvcYupSbfHLoWaYJYkKucw8X04TGFtj/EmVNn5ta0gexxvE66TiGSCtTv2sCfdyOJ07gxuTInEEndFFRj8br+p8Cte1zKBbZ6GM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com; spf=pass smtp.mailfrom=huaweicloud.com; arc=none smtp.client-ip=45.249.212.56 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huaweicloud.com Received: from mail.maildlp.com (unknown [172.19.163.198]) by dggsgout12.his.huawei.com (SkyGuard) with ESMTPS id 4dlsQf69dqzKHMr6 for ; Tue, 6 Jan 2026 21:27:06 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.128]) by mail.maildlp.com (Postfix) with ESMTP id A221640574 for ; Tue, 6 Jan 2026 21:27:46 +0800 (CST) Received: from [10.67.111.176] (unknown [10.67.111.176]) by APP4 (Coremail) with SMTP id gCh0CgAHtfXPDV1pXzxeCw--.1359S2; Tue, 06 Jan 2026 21:27:44 +0800 (CST) Message-ID: Date: Tue, 6 Jan 2026 21:27:42 +0800 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 -next] memcg: Optimize creation performance when LRU_GEN is enabled To: Johannes Weiner Cc: akpm@linux-foundation.org, david@kernel.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, zhengqi.arch@bytedance.com, shakeel.butt@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, lujialin4@huawei.com, chenridong@huawei.com References: <20251119083722.1365680-1-chenridong@huaweicloud.com> <20251126171513.GC135004@cmpxchg.org> Content-Language: en-US From: Chen Ridong In-Reply-To: <20251126171513.GC135004@cmpxchg.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CM-TRANSID:gCh0CgAHtfXPDV1pXzxeCw--.1359S2 X-Coremail-Antispam: 1UD129KBjvJXoW7CryDXr48tF1xKw1rWF45Wrg_yoW8Ary8pF Z8XayDKa18tr9xKrs7tr9rWayFyws3Gr1Yyr1DKrnrZw43Aw12kFy7CF1UW395KF4ku3y2 qFW5Xa4rtw4UCaDanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUv0b4IE77IF4wAFF20E14v26ryj6rWUM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rwA2F7IY1VAKz4 vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_tr0E3s1l84ACjcxK6xIIjxv20xvEc7Cj xVAFwI0_Gr1j6F4UJwA2z4x0Y4vEx4A2jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x 0267AKxVW0oVCq3wAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG 6I80ewAv7VC0I7IYx2IY67AKxVWUJVWUGwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFV Cjc4AY6r1j6r4UM4x0Y48IcVAKI48JM4IIrI8v6xkF7I0E8cxan2IY04v7MxkF7I0En4kS 14v26r4a6rW5MxAIw28IcxkI7VAKI48JMxC20s026xCaFVCjc4AY6r1j6r4UMI8I3I0E5I 8CrVAFwI0_Jr0_Jr4lx2IqxVCjr7xvwVAFwI0_JrI_JrWlx4CE17CEb7AF67AKxVW8ZVWr XwCIc40Y0x0EwIxGrwCI42IY6xIIjxv20xvE14v26r1j6r1xMIIF0xvE2Ix0cI8IcVCY1x 0267AKxVW8JVWxJwCI42IY6xAIw20EY4v20xvaj40_Jr0_JF4lIxAIcVC2z280aVAFwI0_ Jr0_Gr1lIxAIcVC2z280aVCY1x0267AKxVW8JVW8JrUvcSsGvfC2KfnxnUUI43ZEXa7IU0 s2-5UUUUU== X-CM-SenderInfo: hfkh02xlgr0w46kxt4xhlfz01xgou0bp/ On 2025/11/27 1:15, Johannes Weiner wrote: > On Wed, Nov 19, 2025 at 08:37:22AM +0000, Chen Ridong wrote: >> From: Chen Ridong >> >> With LRU_GEN=y and LRU_GEN_ENABLED=n, a performance regression occurs >> when creating a large number of memory cgroups (memcgs): >> >> # time mkdir testcg_{1..10000} >> >> real 0m7.167s >> user 0m0.037s >> sys 0m6.773s >> >> # time mkdir testcg_{1..20000} >> >> real 0m27.158s >> user 0m0.079s >> sys 0m26.270s >> >> In contrast, with LRU_GEN=n, creation of the same number of memcgs >> performs better: >> >> # time mkdir testcg_{1..10000} >> >> real 0m3.386s >> user 0m0.044s >> sys 0m3.009s >> >> # time mkdir testcg_{1..20000} >> >> real 0m6.876s >> user 0m0.075s >> sys 0m6.121s >> >> The root cause is that lru_gen node onlining uses hlist_nulls_add_tail_rcu, >> which traverses the entire list to find the tail. This traversal scales >> with the number of memcgs, even when LRU_GEN is runtime-disabled. > > Can you please look into removing the memcg LRU instead? > > Use mem_cgroup_iter() with a reclaim cookie in shrink_many(), like we > do in shrink_node_memcgs(). > > The memcg LRU is complicated, and it only works for global reclaim; if > you have a subtree with a memory.max at the top, it'll go through > shrink_node_memcgs() already anyway. Hi, all, I previously attempted to remove the memcg LRU [1], but this change introduced a regression that increased kswapd overhead significantly. Now circling back to this issue: does anyone have suggestions on how to address this problem effectively? [1] https://lore.kernel.org/cgroups/0b8ea26f-71f7-4f6d-b0d6-7d42e087a7ed@huaweicloud.com/T/#t -- Best regards, Ridong