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 X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DFF1EC11F65 for ; Tue, 29 Jun 2021 02:37:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C98EE61D0B for ; Tue, 29 Jun 2021 02:37:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231888AbhF2CkT (ORCPT ); Mon, 28 Jun 2021 22:40:19 -0400 Received: from mail.kernel.org ([198.145.29.99]:32768 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231857AbhF2CkS (ORCPT ); Mon, 28 Jun 2021 22:40:18 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 0DEB061A2B; Tue, 29 Jun 2021 02:37:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1624934271; bh=ESap7zNuUQCqQjXySUlVmt3kNR0N5nNLmN2XZAAxv0E=; h=Date:From:To:Subject:In-Reply-To:From; b=y/HDjMbly7Rrcp4K/lKMudHUqGynIXEi5Cev5awrqBcUWJsU03yHH6jMxFRSw3rKp rnir+YP3eqDrM1psHm4n7LmoMyCSObO1oJBWiMsAQm3qUlOe0bHdd6IW9k5Ti5aNrc sBgEZU6Qi2+OWvCD0xOAidW0JiRiVFbgMpttd9z4= Date: Mon, 28 Jun 2021 19:37:50 -0700 From: Andrew Morton To: akpm@linux-foundation.org, duanxiongchun@bytedance.com, guro@fb.com, hannes@cmpxchg.org, linux-mm@kvack.org, mhocko@suse.com, mm-commits@vger.kernel.org, shakeelb@google.com, songmuchun@bytedance.com, torvalds@linux-foundation.org, vdavydov.dev@gmail.com Subject: [patch 086/192] mm: memcontrol: bail out early when !mm in get_mem_cgroup_from_mm Message-ID: <20210629023750.ujb1MXmvq%akpm@linux-foundation.org> In-Reply-To: <20210628193256.008961950a714730751c1423@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org From: Muchun Song Subject: mm: memcontrol: bail out early when !mm in get_mem_cgroup_from_mm When mm is NULL, we do not need to hold rcu lock and call css_tryget for the root memcg. And we also do not need to check !mm in every loop of while. So bail out early when !mm. Link: https://lkml.kernel.org/r/20210417043538.9793-3-songmuchun@bytedance.com Signed-off-by: Muchun Song Acked-by: Johannes Weiner Reviewed-by: Shakeel Butt Acked-by: Roman Gushchin Acked-by: Michal Hocko Cc: Vladimir Davydov Cc: Xiongchun Duan Signed-off-by: Andrew Morton --- mm/memcontrol.c | 25 ++++++++++++++----------- 1 file changed, 14 insertions(+), 11 deletions(-) --- a/mm/memcontrol.c~mm-memcontrol-bail-out-early-when-mm-in-get_mem_cgroup_from_mm +++ a/mm/memcontrol.c @@ -919,20 +919,23 @@ struct mem_cgroup *get_mem_cgroup_from_m if (mem_cgroup_disabled()) return NULL; + /* + * Page cache insertions can happen without an + * actual mm context, e.g. during disk probing + * on boot, loopback IO, acct() writes etc. + * + * No need to css_get on root memcg as the reference + * counting is disabled on the root level in the + * cgroup core. See CSS_NO_REF. + */ + if (unlikely(!mm)) + return root_mem_cgroup; + rcu_read_lock(); do { - /* - * Page cache insertions can happen without an - * actual mm context, e.g. during disk probing - * on boot, loopback IO, acct() writes etc. - */ - if (unlikely(!mm)) + memcg = mem_cgroup_from_task(rcu_dereference(mm->owner)); + if (unlikely(!memcg)) memcg = root_mem_cgroup; - else { - memcg = mem_cgroup_from_task(rcu_dereference(mm->owner)); - if (unlikely(!memcg)) - memcg = root_mem_cgroup; - } } while (!css_tryget(&memcg->css)); rcu_read_unlock(); return memcg; _