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 24FC2C2D0F1 for ; Tue, 31 Mar 2020 17:04:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E49AD20848 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" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731290AbgCaRES (ORCPT ); Tue, 31 Mar 2020 13:04:18 -0400 Received: from mail-wr1-f66.google.com ([209.85.221.66]:33042 "EHLO mail-wr1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726194AbgCaRES (ORCPT ); Tue, 31 Mar 2020 13:04:18 -0400 Received: by mail-wr1-f66.google.com with SMTP id a25so27025913wrd.0 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=sJSARRuo75aDA9fgGmLv9I4lRAa4jcdotGaKHReqFqrxHLV794VxZXE6yIq65VY0/1 6EU/fKSinEzDf5+wEDHE9RK1Q4gtj3wpQJ4r1vm9Voq6dcxFJvaW3SbWiU8LJL5HiECa XMdsL+MLi5z7y23uHZuOcVU+5d5Uh+TM44g+pEkNmRQTL7u/pD774+KFT5UtsotnZprC HX8ZDKoqiRil9ATKWBLJMXnxjjaVxYgb5bho0Uyn5ZFfhdc1klTHU4COXRWo+x/fiAgz Vik8tMa4vT9chRT7v2rCclNuqk8rkCazl8Q85775HcJ1l5op5e81ceF3SVzsrM04/Ta/ IDiQ== X-Gm-Message-State: ANhLgQ3huNNmNskzJn7fiHM36WdYa3LDM0y+wUF/zmxc/W1KvqEmMWpw SJ3MZVnRyv3qFwukOYrtST5KmDCTYq4FPQ== 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> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.