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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4FE9AC433EF for ; Fri, 24 Sep 2021 15:21:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 36D3C610C7 for ; Fri, 24 Sep 2021 15:21:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347076AbhIXPW6 (ORCPT ); Fri, 24 Sep 2021 11:22:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50120 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233132AbhIXPW5 (ORCPT ); Fri, 24 Sep 2021 11:22:57 -0400 Received: from mail-pg1-x529.google.com (mail-pg1-x529.google.com [IPv6:2607:f8b0:4864:20::529]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F1AFCC061571; Fri, 24 Sep 2021 08:21:23 -0700 (PDT) Received: by mail-pg1-x529.google.com with SMTP id 81so6632973pgb.0; Fri, 24 Sep 2021 08:21:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=IWRHE1IksF7N6nES1jMNs1UVooFjxKrNMdCiqYqknKk=; b=UDZUjjkUoxBjfAQ4BcGh4zDS6QNQMedJm0c91MDS4B53lfGBP9hGwV9ieWJBUDrTmP qiSULABKykEaSMPub+/ykJ+xFAhIFg33dF5IfSUeIwMU+fgKn+dVt5+345rOe/v7v9vF yrZO+2N2Gy+eoy5nrHcyzePL3ShWtfm6R2q2LyfMwe9kW1TetvHPgCs4+gQUZZ6kIAyV GHHeXQlN9PrCyn5NNn2SGwoxTONbk5Pb6XSBIJ7AwMOTb5mzGqr/GDHJU+NZFZLXTW74 QzV+R1/l01RJacrzEcTvnwVL5MAhxkawdgzfhBj5BiggvEesd1jjuKbgKKfr6PegH/9s qeyg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=IWRHE1IksF7N6nES1jMNs1UVooFjxKrNMdCiqYqknKk=; b=z5Dy0W7lHsktvjTyV+vuO1UTTO1sHofPsKC4040sI+dGIGniApAHMN5GnBHJSKBK9Z Dd1l1ZKtbGNArQD54puOgX8RQbZlaQqcfYqRUVgcdmp9h/kuvQpWvkJhda7/+mzP8MAf +qyZ6waB//df2K3H8eD8C3dDDgofMBj50CRtCUum6ztpKj8uA/VG2KJ4nIkbMNX+psAI 6Nj/sToKasK7nyENjC6WrIA6N4KPRlgrml2kFBYWAfWyEhJyGShDFMMlxhxQxLMcMg4/ Y3Qqd7XaszIX/WTwDJOVf0F+vlre9ezXLtRhdoRZp2tYpyH7JFwj0dkN7lZX5dmixkAg zghg== X-Gm-Message-State: AOAM531HodKi5mvkzdrjWZf8DEck4MtgXmbME9jKUS3XUsg6aUgAF8jV j/jBTd8ZyMkeFHniUh7j/f30fQ3JBeIUlA== X-Google-Smtp-Source: ABdhPJztuTTCd9H3MpAGQ3cfglzf1jqB8RVKpKosmZw6gUd4JSHLxUQa0SZYZqQ/j8o9+PTszHpRQw== X-Received: by 2002:a63:d34f:: with SMTP id u15mr4232594pgi.200.1632496883270; Fri, 24 Sep 2021 08:21:23 -0700 (PDT) Received: from [192.168.255.10] ([203.205.141.114]) by smtp.gmail.com with ESMTPSA id g8sm9004444pfv.51.2021.09.24.08.21.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 24 Sep 2021 08:21:21 -0700 (PDT) Subject: Re: [PATCH 1/2] mem_cgroup: optimize the atomic count of wb_completion To: Michal Hocko Cc: hannes@cmpxchg.org, vdavydov.dev@gmail.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org References: <1632465983-30525-1-git-send-email-brookxu.cn@gmail.com> <03145735-7764-4cd4-e15b-60402f4b447e@gmail.com> From: "brookxu.cn" Message-ID: Date: Fri, 24 Sep 2021 23:21:19 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.14.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Thanks for your time. On 2021/9/24 10:01 PM, Michal Hocko wrote: > On Fri 24-09-21 21:02:52, brookxu wrote: >> Thanks for your time. >> >> Michal Hocko wrote on 2021/9/24 17:34: >>> On Fri 24-09-21 14:46:22, brookxu wrote: >>>> From: Chunguang Xu >>>> >>>> In order to track inflight foreign writeback, we init >>>> wb_completion.cnt to 1. For normal writeback, this cause >>>> wb_wait_for_completion() to perform meaningless atomic >>>> operations. Since foreign writebacks rarely occur in most >>>> scenarios, we can init wb_completion.cnt to 0 and set >>>> frn.done.cnt to 1. In this way we can avoid unnecessary >>>> atomic operations. >>> >>> Does this lead to any measurable differences? >> >> I created multiple cgroups that performed IO on multiple disks, >> then flushed the cache with sync command, and no measurable >> differences have been observed so far. > > OK, so why do we want to optimize this code? Just a optimization point discovered during the diagnosis, no behavior change. >