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 9712BC433F5 for ; Wed, 23 Mar 2022 01:08:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241022AbiCWBJb (ORCPT ); Tue, 22 Mar 2022 21:09:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58040 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229482AbiCWBJ3 (ORCPT ); Tue, 22 Mar 2022 21:09:29 -0400 Received: from mail-yb1-xb34.google.com (mail-yb1-xb34.google.com [IPv6:2607:f8b0:4864:20::b34]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BB28613F7C for ; Tue, 22 Mar 2022 18:08:00 -0700 (PDT) Received: by mail-yb1-xb34.google.com with SMTP id v35so36740101ybi.10 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=Z3CW1D9seuYe6wKZ24j1fLzdLGLYLo5S5Tedsa0Rxl66f/IvVfXEoIh1m37600a3sy +nitEghVuV3im2O7IwCSYN4f5gwbZmqnRTD/4nycsrr3d7GfhJp0vlTVx7/+RQ8vq0Gm IVmDwtv6jBkNH0KUlyMk1iU9+yLB8FBbBDkqgcGL9KfapQOCE9OpC8s855et+0DFCjVp H9f/n4jllC3pya5qmdRsUMjCf+3s2AFb1F/UDi0Z/16sP92CKyrIcbYQLwbRIwXfLOQP qM5g9z9MJmWIg0mYhXd8Kl7ADehmfEYd50vh585S8Yro2I3pZuASwQ6qD+GW0pm3bv86 vLuA== X-Gm-Message-State: AOAM531JNuPdZZOX5xF9H4KIog+QMXuNQJcZPE/NqztD4mOLktkAXGSX qFoHiZ/DvMRqAcNuAzpFoeVtyTzCoFQ1HE1gkSVP7g== 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" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.