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=-11.4 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL 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 1E729C433E7 for ; Mon, 12 Oct 2020 15:20:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DD03B2087E for ; Mon, 12 Oct 2020 15:20:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="d8hv4SSz" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389562AbgJLPUi (ORCPT ); Mon, 12 Oct 2020 11:20:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46662 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389142AbgJLPUi (ORCPT ); Mon, 12 Oct 2020 11:20:38 -0400 Received: from mail-ej1-x644.google.com (mail-ej1-x644.google.com [IPv6:2a00:1450:4864:20::644]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9FC41C0613D0 for ; Mon, 12 Oct 2020 08:20:36 -0700 (PDT) Received: by mail-ej1-x644.google.com with SMTP id md26so23698016ejb.10 for ; Mon, 12 Oct 2020 08:20:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=ofBD8vZrp3Aut6qdDjM0cDSrd4maOJ5AgeBCWLXm6Do=; b=d8hv4SSz411QexAljC3j/Tqj4gQ5plh6G0e56J7HB7NyqTHgwxYijARNMXD6Zzcv6F Uk9SfTZDglnVkxamc1+uC4jeY9CfHCJkvspF54HtLFoT5DgjnqmB7D0ZHEcMSaTQYfKu I7OONiaTBI9voPEPXXuYJuFhjZ5aAV5noYSqxrxgCGk1Ztb0jIbtjz7xf+AU4EuORa02 RhiCtnlU2OgGIxqj3cblPrKixtv/Nonm1V6CV6F7OLWDXwZZkMYaQqyZ1h3839v0v538 4bh6icuLPCFXlLpTpiLzfeIynqUIhN1/ajS0zhLgZ8fG52wkLG60tiWgTD61EuOXrDdW fttA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=ofBD8vZrp3Aut6qdDjM0cDSrd4maOJ5AgeBCWLXm6Do=; b=ZMPgUbGKdD7qKXDL399ycvtOufLQSboF2ypUi8dg5mQktMDiYxIhnhd52aazLy3o2K je438XlQBOnW/+7LjagHm7WulQ4lltYpRRyEjl/LUPXWJGnshTSd9tVmlX2dX8XP3vRj nZ6gmXpnmkZBQ2EqDquStKGhjo+x3DCF5WFjvbpu1YMBLa/ZRrfBvPPCaxEbOcTf9kB3 CyNzfDfoPQd3Olftf0cYkYzKzDI0/syJ598n/jf8JjhHkVLUYrlSRL/Cm5AZrXV3RzTt EjkUf6I4HUrYTOnTztqiarmoOK/+k/08xmYXtTgGOBEu8F0JSAjRYq83Z6Jg1WC6OIPo ZJaA== X-Gm-Message-State: AOAM533cBvC1G3ZXZv17Oyxux/WQsb1xiDxUtEZp7ipkSdscuS1vVHk9 OGM00J4xAAvgMayZVjc0y9FDQz5YftpYwg6WNYYRtw== X-Google-Smtp-Source: ABdhPJyu6ahJYVJvJfop67WBk+uTXcMLyv/acMUMZyiQrkMfnzFowZh9vozvB0QSHfuY+Z8AeQ/wqYhSa4idaAshq+0= X-Received: by 2002:a17:906:9156:: with SMTP id y22mr29612975ejw.184.1602516035134; Mon, 12 Oct 2020 08:20:35 -0700 (PDT) MIME-Version: 1.0 References: <20201012114940.1317510-1-jannh@google.com> <20201012150738.GF29725@dhcp22.suse.cz> In-Reply-To: <20201012150738.GF29725@dhcp22.suse.cz> From: Jann Horn Date: Mon, 12 Oct 2020 17:20:08 +0200 Message-ID: Subject: Re: [PATCH] proc.5: Document inaccurate RSS due to SPLIT_RSS_COUNTING To: Michal Hocko Cc: Michael Kerrisk-manpages , linux-man , Linux-MM , Mark Mossberg Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-man@vger.kernel.org On Mon, Oct 12, 2020 at 5:07 PM Michal Hocko wrote: > On Mon 12-10-20 13:49:40, Jann Horn wrote: > > Since 34e55232e59f7b19050267a05ff1226e5cd122a5 (introduced back in > > v2.6.34), Linux uses per-thread RSS counters to reduce cache contention on > > the per-mm counters. With a 4K page size, that means that you can end up > > with the counters off by up to 252KiB per thread. > > Do we actually have any strong case to keep this exception to the > accounting? I have no clue. The concept of "concurrently modified cache lines are bad" seemed vaguely reasonable to me... but I have no idea how much impact this actually has on massively multithreaded processes.