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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id AEC47C433EF for ; Wed, 23 Mar 2022 01:08:03 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id EFEF16B0072; Tue, 22 Mar 2022 21:08:02 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id EAE216B0073; Tue, 22 Mar 2022 21:08:02 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D75826B0074; Tue, 22 Mar 2022 21:08:02 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.hostedemail.com [64.99.140.28]) by kanga.kvack.org (Postfix) with ESMTP id C7FF26B0072 for ; Tue, 22 Mar 2022 21:08:02 -0400 (EDT) Received: from smtpin14.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 185A699C for ; Wed, 23 Mar 2022 01:08:02 +0000 (UTC) X-FDA: 79273864404.14.6B292B6 Received: from mail-yb1-f178.google.com (mail-yb1-f178.google.com [209.85.219.178]) by imf19.hostedemail.com (Postfix) with ESMTP id F04581A001E for ; Wed, 23 Mar 2022 01:08:00 +0000 (UTC) Received: by mail-yb1-f178.google.com with SMTP id t33so29209677ybt.12 for ; Tue, 22 Mar 2022 18:08:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20210112.gappssmtp.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=TmS9XqFWOa3npmqi6akNlXoA1MxlQ02g/X1bQSimlGc=; b=eTkTfF7gsKMtnFv0vmxEwLrqozg5VjCqWuUXhurTUUzeR+U70FDajhoT65QVvBq2jk +gYcsgOMJ/1DuyZzyUEYPWah83ud2Xu5pv0Lqv7OZo96rCssZtIIVpY7jJcZRE/Jw5OP aaf/roqvZz0TbF5bcE36CTJLbsk+mCqRtidrsLWZowjhS0VvlnIPbnHN46FkiZET02Iu CORiW9OhJPibBlqvEDZYArUrFavapZu5TFLXG3NsIs7vY8IsBJIwPjeVyCYY/ZuFOStW uGnh+eTIOxFP/28ODOJyNjRsJizlUEp4hAXov/29um/mF2h13qzNWzb7QT/lZBftyhfB SzMw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=TmS9XqFWOa3npmqi6akNlXoA1MxlQ02g/X1bQSimlGc=; b=EqMj/tZbc/e1gPEYWgbqVRWZhyVGXwAb6AhbTa4sSBVozLPv37y/7rp47TcPjaeHUQ xd3Ad+iXuNp/cSbm+JXFvKqIYYNpLHEaRnDsYrRRE2c2uxH/og/pf5MFWKOh1dVusgj3 7VQEnVcDqRdW7Y/Dd2DODroaeNkyumaYabxcqxnqudRwTKyIQD2fYLCK/jfwrrkB8LG4 eLt9s+7PzELgIF9CA7M1+SSa7rZ/KaxxiMHEb6kFNlQBx015C8EC0+ck/juugefg2yfE v/UrfdWuTX07HnliazZ33Fc9wMqRCAllscqgT7lFNvrdLwspwQZM0BinFa8RD+L7ajcQ fAJg== X-Gm-Message-State: AOAM532uS4dQyYyhM4RU9RIM6dq2z5dC08rb6wAzLcHvPn5MVhPRORs9 7QAgjY9Jru4dQJAUz5mQNukGZ0KxqSPiKzmPsXvaSA== X-Google-Smtp-Source: ABdhPJx4K0OSi5k5jpLqjYDqBixWELdbP6OwP88DLE7SrBoeJU+r2PS2vf0aECo2EprR+alXYONOgw8yE7G4D9fF76E= X-Received: by 2002:a25:24d:0:b0:633:6b37:bea1 with SMTP id 74-20020a25024d000000b006336b37bea1mr29032850ybc.427.1647997680003; Tue, 22 Mar 2022 18:08:00 -0700 (PDT) MIME-Version: 1.0 References: <20220309144000.1470138-1-longman@redhat.com> In-Reply-To: <20220309144000.1470138-1-longman@redhat.com> From: Muchun Song Date: Wed, 23 Mar 2022 09:06:03 +0800 Message-ID: Subject: Re: [PATCH-mm v3] mm/list_lru: Optimize memcg_reparent_list_lru_node() To: Waiman Long Cc: Andrew Morton , Linux Memory Management List , LKML , Roman Gushchin Content-Type: text/plain; charset="UTF-8" Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=bytedance-com.20210112.gappssmtp.com header.s=20210112 header.b=eTkTfF7g; spf=pass (imf19.hostedemail.com: domain of songmuchun@bytedance.com designates 209.85.219.178 as permitted sender) smtp.mailfrom=songmuchun@bytedance.com; dmarc=pass (policy=none) header.from=bytedance.com X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: F04581A001E X-Stat-Signature: 8goxhhoa1hg4dmmonb8y7fksax45h9sm X-HE-Tag: 1647997680-646287 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Mar 9, 2022 at 10:40 PM Waiman Long wrote: > > 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. Hi Waiman, Sorry for the late reply. Quick question: what if there is an inflight list_lru_add()? How about the following race? CPU0: CPU1: list_lru_add() spin_lock(&nlru->lock) l = list_lru_from_kmem(memcg) memcg_reparent_objcgs(memcg) memcg_reparent_list_lrus(memcg) memcg_reparent_list_lru() memcg_reparent_list_lru_node() if (!READ_ONCE(nlru->nr_items)) // Miss reparenting return // Assume 0->1 l->nr_items++ // Assume 0->1 nlru->nr_items++ IIUC, we use nlru->lock to serialise this scenario. Thanks.