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 D0150C11F64 for ; Tue, 29 Jun 2021 02:38:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BD6F561D07 for ; Tue, 29 Jun 2021 02:38:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231682AbhF2Cka (ORCPT ); Mon, 28 Jun 2021 22:40:30 -0400 Received: from mail.kernel.org ([198.145.29.99]:32950 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231348AbhF2Cka (ORCPT ); Mon, 28 Jun 2021 22:40:30 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 685BA61D04; Tue, 29 Jun 2021 02:38:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1624934283; bh=N3haBBzWkQNuEOaEtNGYN2d3zDMqfoK5HvKbOnXH3Pc=; h=Date:From:To:Subject:In-Reply-To:From; b=Qlj/muaGildoMi00SSb4lazbLaw24Tf5U9L8rd18gepZN2eaWeaE/NNwF0NbtI+z4 HLp2B3vEjt5F6moW6kxeJwNB0FEClfGNOvD4pUahwc3nihZsm9kZl5apfIVd9f7+7R YvKdksPLh1zGohpl/JM79x8KIJjAPHxkOCbaKmB8= Date: Mon, 28 Jun 2021 19:38:03 -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 090/192] mm: memcontrol: simplify the logic of objcg pinning memcg Message-ID: <20210629023803.yWrgqzH02%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: simplify the logic of objcg pinning memcg The obj_cgroup_release() and memcg_reparent_objcgs() are serialized by the css_set_lock. We do not need to care about objcg->memcg being released in the process of obj_cgroup_release(). So there is no need to pin memcg before releasing objcg. Remove those pinning logic to simplfy the code. There are only two places that modifies the objcg->memcg. One is the initialization to objcg->memcg in the memcg_online_kmem(), another is objcgs reparenting in the memcg_reparent_objcgs(). It is also impossible for the two to run in parallel. So xchg() is unnecessary and it is enough to use WRITE_ONCE(). Link: https://lkml.kernel.org/r/20210417043538.9793-7-songmuchun@bytedance.com Signed-off-by: Muchun Song Acked-by: Johannes Weiner Reviewed-by: Shakeel Butt Acked-by: Roman Gushchin Cc: Michal Hocko Cc: Vladimir Davydov Cc: Xiongchun Duan Signed-off-by: Andrew Morton --- mm/memcontrol.c | 20 ++++++-------------- 1 file changed, 6 insertions(+), 14 deletions(-) --- a/mm/memcontrol.c~mm-memcontrol-simplify-the-logic-of-objcg-pinning-memcg +++ a/mm/memcontrol.c @@ -261,7 +261,6 @@ static void obj_cgroup_uncharge_pages(st static void obj_cgroup_release(struct percpu_ref *ref) { struct obj_cgroup *objcg = container_of(ref, struct obj_cgroup, refcnt); - struct mem_cgroup *memcg; unsigned int nr_bytes; unsigned int nr_pages; unsigned long flags; @@ -291,11 +290,9 @@ static void obj_cgroup_release(struct pe nr_pages = nr_bytes >> PAGE_SHIFT; spin_lock_irqsave(&css_set_lock, flags); - memcg = obj_cgroup_memcg(objcg); if (nr_pages) obj_cgroup_uncharge_pages(objcg, nr_pages); list_del(&objcg->list); - mem_cgroup_put(memcg); spin_unlock_irqrestore(&css_set_lock, flags); percpu_ref_exit(ref); @@ -330,17 +327,12 @@ static void memcg_reparent_objcgs(struct spin_lock_irq(&css_set_lock); - /* Move active objcg to the parent's list */ - xchg(&objcg->memcg, parent); - css_get(&parent->css); - list_add(&objcg->list, &parent->objcg_list); - - /* Move already reparented objcgs to the parent's list */ - list_for_each_entry(iter, &memcg->objcg_list, list) { - css_get(&parent->css); - xchg(&iter->memcg, parent); - css_put(&memcg->css); - } + /* 1) Ready to reparent active objcg. */ + list_add(&objcg->list, &memcg->objcg_list); + /* 2) Reparent active objcg and already reparented objcgs to parent. */ + list_for_each_entry(iter, &memcg->objcg_list, list) + WRITE_ONCE(iter->memcg, parent); + /* 3) Move already reparented objcgs to the parent's list */ list_splice(&memcg->objcg_list, &parent->objcg_list); spin_unlock_irq(&css_set_lock); _