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=-0.9 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 50A29C43331 for ; Tue, 31 Mar 2020 17:04:19 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 07BB320714 for ; Tue, 31 Mar 2020 17:04:19 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chrisdown.name header.i=@chrisdown.name header.b="pZsnQlx7" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 07BB320714 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 AB7F06B0074; Tue, 31 Mar 2020 13:04:18 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A68CF6B0075; Tue, 31 Mar 2020 13:04:18 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9A5126B0078; Tue, 31 Mar 2020 13:04:18 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0117.hostedemail.com [216.40.44.117]) by kanga.kvack.org (Postfix) with ESMTP id 80CED6B0074 for ; Tue, 31 Mar 2020 13:04:18 -0400 (EDT) Received: from smtpin09.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 484E0824805A for ; Tue, 31 Mar 2020 17:04:18 +0000 (UTC) X-FDA: 76656280596.09.horn84_25896bee4fe3a X-HE-Tag: horn84_25896bee4fe3a X-Filterd-Recvd-Size: 3362 Received: from mail-wr1-f66.google.com (mail-wr1-f66.google.com [209.85.221.66]) by imf38.hostedemail.com (Postfix) with ESMTP for ; Tue, 31 Mar 2020 17:04:17 +0000 (UTC) Received: by mail-wr1-f66.google.com with SMTP id h9so26944884wrc.8 for ; Tue, 31 Mar 2020 10:04:17 -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=3MfpJb9zskhXycF6Q+P3UTVTg3zrJvxkcEUgjbQFmfg=; b=pZsnQlx7/55ukASiC3RMQ5r/VpGpt2sx3fZv4j1t5eR0lL10S2G4wpBjHN2OsIgtCn KDGVXMzzasVXuh0uhzi5yOdpNZ+vUfAIwB7wIP+I1kFSUB+EG32TYMcVi5PRnLZKPf4c 0M7AXZdWVpu+HwUc1q3BzVJz1NqBP6gcWGb00= 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=3MfpJb9zskhXycF6Q+P3UTVTg3zrJvxkcEUgjbQFmfg=; b=lQvnwFR60YlM09M2sDKvRG8o9I0JkHBq6uLdmdNLj8AsZCLOq0hQ0nV3jm1YIIbpMT NDuHHxCCbJNZUPoYw2Iqh5sX9g2OY+JcRj+TdNFHUf7IoEVd2OU+cTCCa49OAlt133EA I4xCd8xFI2yCuaaIdWU12rJzT6q2TlvEg68Zl54nbAXe+ojqd5CKWnTT/06XkEr189k6 uAE2b1TVDMRnfrBOA2rq4IDuJkqeETOEnfYtMhiW1c7UPQuJgqj3ory3PsZvTM8pAITX cKgV968apFLPd2SB0BbLdOPPDQMLLeaLUWIVjTOdbo7uLxqgXuX95cqz1/y7KU65wwfV i3Ig== X-Gm-Message-State: ANhLgQ2193WqLqygicqqYXglMAJ0zyvAVWy0Iej64iCYd6QOEr9uSXce Da7OhbtzzkYudv6mTNZULpu3tw== X-Google-Smtp-Source: ADFU+vsyRM3LsPUxIXkBsY97QN1fJN2ENc2TMRygohrVkAY6lDjYhTsc8BzhHSDzgxzhXYr4e9HAFA== X-Received: by 2002:adf:916f:: with SMTP id j102mr20527218wrj.335.1585674256639; Tue, 31 Mar 2020 10:04:16 -0700 (PDT) Received: from localhost ([2620:10d:c092:180::1:27bd]) by smtp.gmail.com with ESMTPSA id r9sm4700820wma.47.2020.03.31.10.04.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 Mar 2020 10:04:16 -0700 (PDT) Date: Tue, 31 Mar 2020 18:04:10 +0100 From: Chris Down To: Michal Hocko Cc: Andrew Morton , Johannes Weiner , Jakub Kicinski , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH] mm, memcg: Do not high throttle allocators based on wraparound Message-ID: <20200331170410.GB972283@chrisdown.name> References: <20200331152424.GA1019937@chrisdown.name> <20200331155752.GN30449@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20200331155752.GN30449@dhcp22.suse.cz> 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: Michal Hocko writes: >I find this paragraph rather confusing. This is essentially an unsigned >underflow when any of the memcg up the hierarchy is below the high >limit, right? There doesn't really seem anything complex in such a >hierarchy. The conditions to trigger the bug itself are easy, but having it obviously visible in tests requires a moderately complex hierarchy, since in the basic case ancestor_usage is "similar enough" to the test leaf cgroup's usage.