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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 C5705C282C8 for ; Mon, 28 Jan 2019 13:35:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8329E2148E for ; Mon, 28 Jan 2019 13:35:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548682518; bh=ThV8zaiDoRORDOQgNK58MhtDRSznnSy8HqC2DbKcuyw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=hCiHVCU92OpZfsjCJHPaycHBiJvPFeQ8Ah/GxkA3u9UKc2bRkJv4vOGhrM+ijAhRh x1ugqqCCVWQSVvzuihKzqEvQMlUscqZbyFQ3JfdSmIzuJGHTYdA7NQIYsrrXHsxVXv hPf0H7gZzhd7gUd2zuDLKyrokPGVWVDJNYK3Z2Bk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726719AbfA1NfR (ORCPT ); Mon, 28 Jan 2019 08:35:17 -0500 Received: from mx2.suse.de ([195.135.220.15]:44070 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726647AbfA1NfQ (ORCPT ); Mon, 28 Jan 2019 08:35:16 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 436DFABB1; Mon, 28 Jan 2019 13:35:15 +0000 (UTC) Date: Mon, 28 Jan 2019 14:35:14 +0100 From: Michal Hocko To: David Hildenbrand Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Mel Gorman , "Kirill A. Shutemov" , Naoya Horiguchi , Jan Kara , Andrea Arcangeli , Dominik Brodowski , Matthew Wilcox , Vratislav Bendel , Rafael Aquini Subject: Re: [PATCH RFC] mm: migrate: don't rely on PageMovable() of newpage after unlocking it Message-ID: <20190128133514.GL18811@dhcp22.suse.cz> References: <20190128121609.9528-1-david@redhat.com> <20190128130709.GJ18811@dhcp22.suse.cz> <20190128132146.GK18811@dhcp22.suse.cz> <17e7d7e4-f4ca-a681-93e5-92a0c285be14@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <17e7d7e4-f4ca-a681-93e5-92a0c285be14@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 28-01-19 14:22:52, David Hildenbrand wrote: > On 28.01.19 14:21, Michal Hocko wrote: > > On Mon 28-01-19 14:14:28, David Hildenbrand wrote: > >> On 28.01.19 14:07, Michal Hocko wrote: > >>> On Mon 28-01-19 13:16:09, David Hildenbrand wrote: > >>> [...] > >>>> My theory: > >>>> > >>>> In __unmap_and_move(), we lock the old and newpage and perform the > >>>> migration. In case of vitio-balloon, the new page will become > >>>> movable, the old page will no longer be movable. > >>>> > >>>> However, after unlocking newpage, I think there is nothing stopping > >>>> the newpage from getting dequeued and freed by virtio-balloon. This > >>>> will result in the newpage > >>>> 1. No longer having PageMovable() > >>>> 2. Getting moved to the local list before finally freeing it (using > >>>> page->lru) > >>> > >>> Does that mean that the virtio-balloon can change the Movable state > >>> while there are other users of the page? Can you point to the code that > >>> does it? How come this can be safe at all? Or is the PageMovable stable > >>> only under the page lock? > >>> > >> > >> PageMovable is stable under the lock. The relevant instructions are in > >> > >> mm/balloon_compaction.c and include/linux/balloon_compaction.h > > > > OK, I have just checked __ClearPageMovable and it indeed requires > > PageLock. Then we also have to move is_lru = __PageMovable(page) after > > the page lock. > > > > I assume that is fine as is as the page is isolated? (yes, it will be > modified later when moving but we are interested in the original state) OK, I've missed that the page is indeed isolated. Then the patch makes sense to me. -- Michal Hocko SUSE Labs