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 414566453 for ; Tue, 22 Mar 2022 21:45:45 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0AF3BC340EC; Tue, 22 Mar 2022 21:45:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1647985545; bh=J09gnwx+pM4OrqpRiCN3GoxRGIEM2JJo77DhAVWt2/o=; h=Date:To:From:In-Reply-To:Subject:From; b=Z29Wx5GtoDHoMxP/UeJv0ahkKwvT7trNuaLYNZYmdV5hP9wwM38v/0M0h1JnS6uZ3 4ZAyhMilkOT0yTM9hfGX3ypoYuhRsMWTMu1iPLN9uBVbQnomGeh5K/4aAK4LkGR9hm jbJy5M2iUhFSr+KzeM25ZzroUYyWoISJFWA21BzI= Date: Tue, 22 Mar 2022 14:45:44 -0700 To: songmuchun@bytedance.com,shakeelb@google.com,roman.gushchin@linux.dev,mhocko@suse.com,hannes@cmpxchg.org,longman@redhat.com,akpm@linux-foundation.org,patches@lists.linux.dev,linux-mm@kvack.org,mm-commits@vger.kernel.org,torvalds@linux-foundation.org,akpm@linux-foundation.org From: Andrew Morton In-Reply-To: <20220322143803.04a5e59a07e48284f196a2f9@linux-foundation.org> Subject: [patch 142/227] mm/list_lru: optimize memcg_reparent_list_lru_node() Message-Id: <20220322214545.0AF3BC340EC@smtp.kernel.org> Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: From: Waiman Long Subject: mm/list_lru: optimize memcg_reparent_list_lru_node() Since commit 2c80cd57c743 ("mm/list_lru.c: fix list_lru_count_node() to be race free"), we are tracking the total number of lru entries in a list_lru_node in its nr_items field. In the case of memcg_reparent_list_lru_node(), there is nothing to be done if nr_items is 0. We don't even need to take the nlru->lock as no new lru entry could be added by a racing list_lru_add() to the draining src_idx memcg at this point. On systems that serve a lot of containers, it is possible that there can be thousands of list_lru's present due to the fact that each container may mount its own container specific filesystems. As a typical container uses only a few cpus, it is likely that only the list_lru_node that contains those cpus will be utilized while the rests may be empty. In other words, there can be a lot of list_lru_node with 0 nr_items. By skipping a lock/unlock operation and loading a cacheline from memcg_lrus, a sizeable number of cpu cycles can be saved. That can be substantial if we are talking about thousands of list_lru_node's with 0 nr_items. Link: https://lkml.kernel.org/r/20220309144000.1470138-1-longman@redhat.com Signed-off-by: Waiman Long Reviewed-by: Roman Gushchin Cc: Muchun Song Cc: Michal Hocko Cc: Johannes Weiner Cc: Shakeel Butt Signed-off-by: Andrew Morton --- mm/list_lru.c | 6 ++++++ 1 file changed, 6 insertions(+) --- a/mm/list_lru.c~mm-list_lru-optimize-memcg_reparent_list_lru_node +++ a/mm/list_lru.c @@ -395,6 +395,12 @@ static void memcg_reparent_list_lru_node struct list_lru_one *src, *dst; /* + * If there is no lru entry in this nlru, we can skip it immediately. + */ + if (!READ_ONCE(nlru->nr_items)) + return; + + /* * Since list_lru_{add,del} may be called under an IRQ-safe lock, * we have to use IRQ-safe primitives here to avoid deadlock. */ _ From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9FA94C43217 for ; Tue, 22 Mar 2022 21:45:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236486AbiCVVr0 (ORCPT ); Tue, 22 Mar 2022 17:47:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33734 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236518AbiCVVrP (ORCPT ); Tue, 22 Mar 2022 17:47:15 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CB8875F8F0 for ; Tue, 22 Mar 2022 14:45:47 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 7148CB81D77 for ; Tue, 22 Mar 2022 21:45:46 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0AF3BC340EC; Tue, 22 Mar 2022 21:45:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1647985545; bh=J09gnwx+pM4OrqpRiCN3GoxRGIEM2JJo77DhAVWt2/o=; h=Date:To:From:In-Reply-To:Subject:From; b=Z29Wx5GtoDHoMxP/UeJv0ahkKwvT7trNuaLYNZYmdV5hP9wwM38v/0M0h1JnS6uZ3 4ZAyhMilkOT0yTM9hfGX3ypoYuhRsMWTMu1iPLN9uBVbQnomGeh5K/4aAK4LkGR9hm jbJy5M2iUhFSr+KzeM25ZzroUYyWoISJFWA21BzI= Date: Tue, 22 Mar 2022 14:45:44 -0700 To: songmuchun@bytedance.com, shakeelb@google.com, roman.gushchin@linux.dev, mhocko@suse.com, hannes@cmpxchg.org, longman@redhat.com, akpm@linux-foundation.org, patches@lists.linux.dev, linux-mm@kvack.org, mm-commits@vger.kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org From: Andrew Morton In-Reply-To: <20220322143803.04a5e59a07e48284f196a2f9@linux-foundation.org> Subject: [patch 142/227] mm/list_lru: optimize memcg_reparent_list_lru_node() Message-Id: <20220322214545.0AF3BC340EC@smtp.kernel.org> Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org From: Waiman Long Subject: mm/list_lru: optimize memcg_reparent_list_lru_node() Since commit 2c80cd57c743 ("mm/list_lru.c: fix list_lru_count_node() to be race free"), we are tracking the total number of lru entries in a list_lru_node in its nr_items field. In the case of memcg_reparent_list_lru_node(), there is nothing to be done if nr_items is 0. We don't even need to take the nlru->lock as no new lru entry could be added by a racing list_lru_add() to the draining src_idx memcg at this point. On systems that serve a lot of containers, it is possible that there can be thousands of list_lru's present due to the fact that each container may mount its own container specific filesystems. As a typical container uses only a few cpus, it is likely that only the list_lru_node that contains those cpus will be utilized while the rests may be empty. In other words, there can be a lot of list_lru_node with 0 nr_items. By skipping a lock/unlock operation and loading a cacheline from memcg_lrus, a sizeable number of cpu cycles can be saved. That can be substantial if we are talking about thousands of list_lru_node's with 0 nr_items. Link: https://lkml.kernel.org/r/20220309144000.1470138-1-longman@redhat.com Signed-off-by: Waiman Long Reviewed-by: Roman Gushchin Cc: Muchun Song Cc: Michal Hocko Cc: Johannes Weiner Cc: Shakeel Butt Signed-off-by: Andrew Morton --- mm/list_lru.c | 6 ++++++ 1 file changed, 6 insertions(+) --- a/mm/list_lru.c~mm-list_lru-optimize-memcg_reparent_list_lru_node +++ a/mm/list_lru.c @@ -395,6 +395,12 @@ static void memcg_reparent_list_lru_node struct list_lru_one *src, *dst; /* + * If there is no lru entry in this nlru, we can skip it immediately. + */ + if (!READ_ONCE(nlru->nr_items)) + return; + + /* * Since list_lru_{add,del} may be called under an IRQ-safe lock, * we have to use IRQ-safe primitives here to avoid deadlock. */ _