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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 5940FC433F5 for ; Fri, 24 Sep 2021 14:02:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 417EC610F7 for ; Fri, 24 Sep 2021 14:02:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346687AbhIXODf (ORCPT ); Fri, 24 Sep 2021 10:03:35 -0400 Received: from smtp-out1.suse.de ([195.135.220.28]:44418 "EHLO smtp-out1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346646AbhIXOD3 (ORCPT ); Fri, 24 Sep 2021 10:03:29 -0400 Received: from relay1.suse.de (relay1.suse.de [149.44.160.133]) by smtp-out1.suse.de (Postfix) with ESMTP id A70D922441; Fri, 24 Sep 2021 14:01:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1632492114; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=dmtnQno5WAWYAwYyFrab1anhvWM53F0z0kxqT7Xw1k8=; b=nRbMdbYvkFc6B1k0PP9awPeMPmfeeTv3mNv/96g99J9pGTDnAplSR8wAChc7G9xWP98BoD gCteNo/1Cqk0O16O2ECCm4MqbJoI9lTh3LJINeTuulQtUUK0k+fNPQIAcU5EIOz6TGODVL LwxJX5IWJ/ZTtg+XuAvIrWloxnzE3jg= Received: from suse.cz (unknown [10.100.201.86]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay1.suse.de (Postfix) with ESMTPS id 9052025DA7; Fri, 24 Sep 2021 14:01:54 +0000 (UTC) Date: Fri, 24 Sep 2021 16:01:51 +0200 From: Michal Hocko To: brookxu Cc: hannes@cmpxchg.org, vdavydov.dev@gmail.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org Subject: Re: [PATCH 1/2] mem_cgroup: optimize the atomic count of wb_completion Message-ID: References: <1632465983-30525-1-git-send-email-brookxu.cn@gmail.com> <03145735-7764-4cd4-e15b-60402f4b447e@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <03145735-7764-4cd4-e15b-60402f4b447e@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? -- Michal Hocko SUSE Labs