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=-1.0 required=3.0 tests=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 1E6F6C3F2D3 for ; Mon, 16 Mar 2020 09:21:03 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id DCBE120674 for ; Mon, 16 Mar 2020 09:21:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DCBE120674 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 689E76B0003; Mon, 16 Mar 2020 05:21:02 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 639F76B0005; Mon, 16 Mar 2020 05:21:02 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 54FAB6B0007; Mon, 16 Mar 2020 05:21:02 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0254.hostedemail.com [216.40.44.254]) by kanga.kvack.org (Postfix) with ESMTP id 3BAD86B0003 for ; Mon, 16 Mar 2020 05:21:02 -0400 (EDT) Received: from smtpin23.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 0B303180AD802 for ; Mon, 16 Mar 2020 09:21:02 +0000 (UTC) X-FDA: 76600681164.23.air26_433181cbfba5b X-HE-Tag: air26_433181cbfba5b X-Filterd-Recvd-Size: 5678 Received: from mail-wm1-f46.google.com (mail-wm1-f46.google.com [209.85.128.46]) by imf12.hostedemail.com (Postfix) with ESMTP for ; Mon, 16 Mar 2020 09:21:01 +0000 (UTC) Received: by mail-wm1-f46.google.com with SMTP id g62so17122258wme.1 for ; Mon, 16 Mar 2020 02:21:01 -0700 (PDT) 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=gpxt45thOiwYDJ5g1pO2m1tlgc7KWRmLIsWLSSokj8o=; b=tJvVq+SyS5thSTAbugmQlAIKDb0nXAay8yjCfr3ltIsaUk7mKun9eEtNcx3YFm2bH0 DJhIiyu+3pvB8Ppf0w4/0mqms8qNkk1J2sRDTH+wxdB0nXAJwIY/U1uSqnReW5AS5yQL IyoU2+tuLz0ZQZIt1T4cCJ8T91+sY/vtsc2ClpNcj7ZJknvnQtVkYOWkIZ2Y/8+Hw9A1 DPCQNET/1MXdk6b3ml1t0cY3OvpA88NhAtF4yqAHd+Lp6Y2pNW+Z/nqF26Oy6WKlB3Pl JRrs/59UtO4Nkh2K3sip/cnbW1PJIk2XRSYsdu0B0adCLgYFvGvgpqlufdCljYVPWgQ8 jNCg== X-Gm-Message-State: ANhLgQ06647kCmcFFTLKekZcenpn1rmqbrj35WLKYtHd9yiDK1xONEGb w1bwVxMxCCZJ1+MDB9YHmxg= X-Google-Smtp-Source: ADFU+vtaeMCR2Ww10SJIeSbFOcdwi1jjYcl9WBPQwNgDIPmCJSXZrB0Fv0sl5MK4g5sOxGhivEEOWw== X-Received: by 2002:a1c:156:: with SMTP id 83mr27637518wmb.151.1584350460481; Mon, 16 Mar 2020 02:21:00 -0700 (PDT) Received: from localhost (ip-37-188-254-25.eurotel.cz. [37.188.254.25]) by smtp.gmail.com with ESMTPSA id b5sm22221872wrw.86.2020.03.16.02.20.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 16 Mar 2020 02:20:59 -0700 (PDT) Date: Mon, 16 Mar 2020 10:20:52 +0100 From: Michal Hocko To: Minchan Kim Cc: Jann Horn , Linux-MM , kernel list , Daniel Colascione , Dave Hansen , "Joel Fernandes (Google)" , Andrew Morton Subject: Re: interaction of MADV_PAGEOUT with CoW anonymous mappings? Message-ID: <20200316092052.GD11482@dhcp22.suse.cz> References: <20200312082248.GS23944@dhcp22.suse.cz> <20200312201602.GA68817@google.com> <20200312204155.GE23944@dhcp22.suse.cz> <20200313020851.GD68817@google.com> <20200313080546.GA21007@dhcp22.suse.cz> <20200313205941.GA78185@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200313205941.GA78185@google.com> 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 Fri 13-03-20 13:59:41, Minchan Kim wrote: > On Fri, Mar 13, 2020 at 09:05:46AM +0100, Michal Hocko wrote: > > On Thu 12-03-20 19:08:51, Minchan Kim wrote: > > > On Thu, Mar 12, 2020 at 09:41:55PM +0100, Michal Hocko wrote: > > > > On Thu 12-03-20 13:16:02, Minchan Kim wrote: > > > > > On Thu, Mar 12, 2020 at 09:22:48AM +0100, Michal Hocko wrote: > > > > [...] > > > > > > From eca97990372679c097a88164ff4b3d7879b0e127 Mon Sep 17 00:00:00 2001 > > > > > > From: Michal Hocko > > > > > > Date: Thu, 12 Mar 2020 09:04:35 +0100 > > > > > > Subject: [PATCH] mm: do not allow MADV_PAGEOUT for CoW pages > > > > > > > > > > > > Jann has brought up a very interesting point [1]. While shared pages are > > > > > > excluded from MADV_PAGEOUT normally, CoW pages can be easily reclaimed > > > > > > that way. This can lead to all sorts of hard to debug problems. E.g. > > > > > > performance problems outlined by Daniel [2]. There are runtime > > > > > > environments where there is a substantial memory shared among security > > > > > > domains via CoW memory and a easy to reclaim way of that memory, which > > > > > > MADV_{COLD,PAGEOUT} offers, can lead to either performance degradation > > > > > > in for the parent process which might be more privileged or even open > > > > > > side channel attacks. The feasibility of the later is not really clear > > > > > > > > > > I am not sure it's a good idea to mention performance stuff because > > > > > it's rather arguble. You and Johannes already pointed it out when I sbumit > > > > > early draft which had shared page filtering out logic due to performance > > > > > reason. You guys suggested the shared pages has higher chance to be touched > > > > > so that if it's really hot pages, that whould keep in the memory. I agree. > > > > > > > > Yes, the hot memory is likely to be referenced but the point was an > > > > unexpected latency because of the major fault. I have to say that I have > > > > > > I don't understand your point here. If it's likely to be referenced > > > among several processes, it doesn't have the major fault latency. > > > What's your point here? > > > > a) the particular CoW page might be cold enough to be reclaimed and b) > > If it is, that means it's *cold* so it's really worth to be reclaimed. > > > nothing really prevents the MADV_PAGEOUT to be called faster than the > > reference bit being readded. > > Yeb, that's undesirable. I should admit it was not intended when I implemented > PAGEOUT. The thing is page_check_references clears access bit of pte for every > process are sharing the page so that two times MADV_PAGEOUT from a process could > evict the page. That's the really bug. I do not really think this is a bug. This is a side effect of the reclaim process and we do not really want MADV_{PAGEOUT,COLD} behave differently here because then the behavior would be even harder to understand. -- Michal Hocko SUSE Labs