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=-3.9 required=3.0 tests=BAYES_00,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 E3DCDC43466 for ; Mon, 21 Sep 2020 14:28:42 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 65CEB221EC for ; Mon, 21 Sep 2020 14:28:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="kTgxnzS7" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 65CEB221EC Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 9D8436B00D0; Mon, 21 Sep 2020 10:28:41 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 960CA6B00D1; Mon, 21 Sep 2020 10:28:41 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 828546B00D2; Mon, 21 Sep 2020 10:28:41 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0205.hostedemail.com [216.40.44.205]) by kanga.kvack.org (Postfix) with ESMTP id 689616B00D0 for ; Mon, 21 Sep 2020 10:28:41 -0400 (EDT) Received: from smtpin08.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 15501181AEF15 for ; Mon, 21 Sep 2020 14:28:41 +0000 (UTC) X-FDA: 77287299642.08.drum62_0507e6f27145 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin08.hostedemail.com (Postfix) with ESMTP id E6C831819E773 for ; Mon, 21 Sep 2020 14:28:40 +0000 (UTC) X-HE-Tag: drum62_0507e6f27145 X-Filterd-Recvd-Size: 4659 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf36.hostedemail.com (Postfix) with ESMTP for ; Mon, 21 Sep 2020 14:28:40 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1600698519; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=1RdoYXKwEjK4J3d1DYrl5vaMGQPhf2n+JMMWMOYRwtU=; b=kTgxnzS7teOS36PrXh0wm+C0EApapZblNjjrebqXoJ5ChnxL4I+xPE9HMdxVW9xlGYz6eg rK0EppRHDdkJma4AyUvZAvg18F2k2CLiiNFPHUNLRyPeGGLStbtax09rA13XWRpQXwxuZy /tlacC6+W7gvF48ZV17gPjianbo/3Fk= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 28DB2B12E; Mon, 21 Sep 2020 14:29:15 +0000 (UTC) Date: Mon, 21 Sep 2020 16:28:34 +0200 From: Michal Hocko To: Peter Xu Cc: Tejun Heo , Christian Brauner , Linus Torvalds , Jason Gunthorpe , John Hubbard , Leon Romanovsky , Linux-MM , Linux Kernel Mailing List , "Maya B . Gokhale" , Yang Shi , Marty Mcfadden , Kirill Shutemov , Oleg Nesterov , Jann Horn , Jan Kara , Kirill Tkhai , Andrea Arcangeli , Christoph Hellwig , Andrew Morton Subject: Re: [PATCH 1/4] mm: Trial do_wp_page() simplification Message-ID: <20200921142834.GL12990@dhcp22.suse.cz> References: <20200916174804.GC8409@ziepe.ca> <20200916184619.GB40154@xz-x1> <20200917112538.GD8409@ziepe.ca> <20200917193824.GL8409@ziepe.ca> <20200918164032.GA5962@xz-x1> <20200921134200.GK12990@dhcp22.suse.cz> <20200921141830.GE5962@xz-x1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200921141830.GE5962@xz-x1> 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 Mon 21-09-20 10:18:30, Peter Xu wrote: > Hi, Michal, > > On Mon, Sep 21, 2020 at 03:42:00PM +0200, Michal Hocko wrote: [...] > > I have only now > > learned about this feature so I am not deeply familiar with all the > > details and I might be easily wrong. Normally all the cgroup aware > > resources are accounted to the parent's cgroup. For memcg that includes > > all the page tables, early CoW and other allocations with __GFP_ACCOUNT. > > IIUC CLONE_INTO_CGROUP properly then this hasn't changed as the child is > > associated to its new cgroup (and memcg) only in cgroup_post_fork. If > > that is correct then we might have quite a lot of resources bound to > > child's lifetime but accounted to the parent's memcg which can lead to > > all sorts of interesting problems (e.g. unreclaimable memory - even by > > the oom killer). > > Right that's one of the things that I'm confused too, on that if we always > account to the parent, then when the child quits whether we uncharge them or > not, and how.. Not sure whether the accounting of the parent could steadily > grow as it continues the fork()s. > > So is it by design that we account all these to the parents? Let me try to clarify a bit further my concern. Without CLONE_INTO_CGROUP this makes some sense. Because both parent and child will live in the same cgroup. All the charges are reference counted so they will be released when the respective resource gets freed (e.g. page table released or the backing page dropped) irrespective of the current cgroup the owner is living in. Fundamentaly CLONE_INTO_CGROUP is similar to regular fork + move to the target cgroup after the child gets executed. So in principle there shouldn't be any big difference. Except that the move has to be explicit and the the child has to have enough privileges to move itself. I am not completely sure about CLONE_INTO_CGROUP model though. According to man clone(2) it seems that O_RDONLY for the target cgroup directory is sufficient. That seems much more relaxed IIUC and it would allow to fork into a different cgroup while keeping a lot of resources in the parent's proper. -- Michal Hocko SUSE Labs