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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 AF495C433DB for ; Wed, 20 Jan 2021 07:50:00 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 13FCE23131 for ; Wed, 20 Jan 2021 07:49:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 13FCE23131 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 710EF6B0007; Wed, 20 Jan 2021 02:49:59 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 6989D6B0008; Wed, 20 Jan 2021 02:49:59 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 560296B000A; Wed, 20 Jan 2021 02:49:59 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0142.hostedemail.com [216.40.44.142]) by kanga.kvack.org (Postfix) with ESMTP id 3C4446B0007 for ; Wed, 20 Jan 2021 02:49:59 -0500 (EST) Received: from smtpin20.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 054F3180AD81F for ; Wed, 20 Jan 2021 07:49:59 +0000 (UTC) X-FDA: 77725379718.20.crown39_4111af827558 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin20.hostedemail.com (Postfix) with ESMTP id D13C0180C07AF for ; Wed, 20 Jan 2021 07:49:58 +0000 (UTC) X-HE-Tag: crown39_4111af827558 X-Filterd-Recvd-Size: 2363 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf44.hostedemail.com (Postfix) with ESMTP for ; Wed, 20 Jan 2021 07:49:58 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1611128997; 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=QeFIPCKf1lzYZ5NNZ/UyihM0FPQ4ig48O6bHj3KSVc0=; b=pjKh/cmX3L7lWbEKaS4FMhCZzGKLMOMKo9InQl9tWIyGjOGZkXfH3nRZUV7+XPf5Fka8W1 7ADICESjNintsIualGfn3VWpnmRIbn34rk7Jd14bymn6XA42bxGdXyDDCwgjLrm0qKf4pG 8jKoVVesER20mZI+dx71Qxm8MDXlZ4U= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 49F69AAAE; Wed, 20 Jan 2021 07:49:57 +0000 (UTC) Date: Wed, 20 Jan 2021 08:49:56 +0100 From: Michal Hocko To: Johannes Weiner Cc: Muchun Song , vdavydov.dev@gmail.com, akpm@linux-foundation.org, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: memcontrol: skip propagate percpu vmstat values to current memcg Message-ID: <20210120074956.GB9371@dhcp22.suse.cz> References: <20210119052744.96765-1-songmuchun@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Tue 19-01-21 11:58:42, Johannes Weiner wrote: > On Tue, Jan 19, 2021 at 01:27:44PM +0800, Muchun Song wrote: > > The current memcg will be freed soon, so updating it's vmstat and > > vmevent values is pointless. Just skip updating it. > > > > Signed-off-by: Muchun Song > > Oof, that's pretty subtle! Somebody trying to refactor that code for > other purposes may not immediately notice that optimization and add > potentially tedious bugs. Absolutely agreed! > How much does this save? Cgroup creation and deletion isn't really > considered a hot path. It takes global locks and such... This is not the first time when an (micro)optimization is posted without any data showing benefit or otherwise appealing justification. Sigh. -- Michal Hocko SUSE Labs