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=-0.8 required=3.0 tests=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 CA9DCC54FCB for ; Fri, 24 Apr 2020 13:05:58 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 90A5420767 for ; Fri, 24 Apr 2020 13:05:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chrisdown.name header.i=@chrisdown.name header.b="A45AEe6y" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 90A5420767 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=chrisdown.name Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 3B2A48E0005; Fri, 24 Apr 2020 09:05:58 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 33BD38E0003; Fri, 24 Apr 2020 09:05:58 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2034A8E0005; Fri, 24 Apr 2020 09:05:58 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0231.hostedemail.com [216.40.44.231]) by kanga.kvack.org (Postfix) with ESMTP id 041338E0003 for ; Fri, 24 Apr 2020 09:05:57 -0400 (EDT) Received: from smtpin26.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id A6A8A181AC9BF for ; Fri, 24 Apr 2020 13:05:57 +0000 (UTC) X-FDA: 76742771154.26.war83_5114b1329a303 X-HE-Tag: war83_5114b1329a303 X-Filterd-Recvd-Size: 3921 Received: from mail-wr1-f65.google.com (mail-wr1-f65.google.com [209.85.221.65]) by imf29.hostedemail.com (Postfix) with ESMTP for ; Fri, 24 Apr 2020 13:05:57 +0000 (UTC) Received: by mail-wr1-f65.google.com with SMTP id s10so10741681wrr.0 for ; Fri, 24 Apr 2020 06:05:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chrisdown.name; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=auGOkVlJG2i/aNN/COO5M+dD12KEjmYZImaR8ZZh+Do=; b=A45AEe6yfVyjlMv+DgFM5b2k0CVtja1wyfRRHnVuekxaPlmO3O1HUAiOrgoqi+tRCO US8zRMF+aD+swuxvP8/YYNTnaa0XAPTasxRhEkxpwV4AFfk1gS64ztgAWw2d38OMAzPD hZG3jVXP7M7BdsgM2hHwZr8qx7kzrIRqhCsAs= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=auGOkVlJG2i/aNN/COO5M+dD12KEjmYZImaR8ZZh+Do=; b=aCbAPklC1avfsWlqRphsrHfC2ThAMwqGsxjubTqODQmkP/7hAhROcgwbp3QyrbCy0w L7zNkrEwQ38D4liyh4DzPsFGeabk2SnyfGLtc52qUASu2A5tMNtwA5Otu25ztX4jkTq2 KEMKkokLNuEbzjwKHvA5ukAlMmUu3BKXKWdyPRWWGqJBzDC5xBGNF2lG4hLt0+jK6o1g WUPXR+QkLXMnU/dmHTy84PcsUHrVWepRxBqYxuOuEKGHydSFyWHHKveojValJEPjsXBu yaySOq+5RXRB2rFRUYiw0gvGGWwMKwZPpnnyOJMK69szgKkObacF5RSjwZ98zShtMpXV wQvQ== X-Gm-Message-State: AGi0PuYs9GpvSTMPHVKVLEXMar4XjZFhepipjdEdqhozNA8dOI7N3iz8 +eM11pQbcUpjWTFfbz8FY7K/Qw== X-Google-Smtp-Source: APiQypLAf59/tHRnRR8kS5JUaX+dtrefzQUXMjAUpoLtD45sUqgmTfRhIn2cXi9cw5f+t1BM/LS1cA== X-Received: by 2002:a5d:610e:: with SMTP id v14mr10792558wrt.159.1587733555924; Fri, 24 Apr 2020 06:05:55 -0700 (PDT) Received: from localhost ([2620:10d:c092:180::1:5fe8]) by smtp.gmail.com with ESMTPSA id y63sm2877129wmg.21.2020.04.24.06.05.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 24 Apr 2020 06:05:55 -0700 (PDT) Date: Fri, 24 Apr 2020 14:05:54 +0100 From: Chris Down To: Yafang Shao Cc: Andrew Morton , Michal Hocko , Vladimir Davydov , Linux MM , Roman Gushchin , stable@vger.kernel.org, Johannes Weiner Subject: Re: [PATCH] mm, memcg: fix wrong mem cgroup protection Message-ID: <20200424130554.GA1462690@chrisdown.name> References: <20200423061629.24185-1-laoar.shao@gmail.com> <20200423153323.GA1318256@chrisdown.name> <20200424121836.GA1379200@chrisdown.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed 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: I'm not debating whether your test case is correct or not, or whether the numbers are correct or not. The point is that 3 out of 4 people from mm list who have looked at this patch have no idea what it's trying to do, why it's important, or why these numbers *should* necessarily be wrong. It's good that you have provided a way to demonstrate the effects of your changes, but one can't solve cognitive gaps with testing. If one could, then things like TDD would be effective on complex projects -- but they aren't[0]. We're really getting off in the weeds here, though. I just want to make it clear to you that if you think "more testing" is a solution to kernel ailments like this, you're going to be disappointed. 0: http://people.brunel.ac.uk/~csstmms/FucciEtAl_ESEM2016.pdf