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 51FAAC282CD for ; Mon, 28 Jan 2019 13:21:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2040B20989 for ; Mon, 28 Jan 2019 13:21:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548681710; bh=w6FZaaY4zhm8+oTwD2m/Hm+78DVl4f3Em1MtgXA+a+8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=cvUgpV5UEdZnWedZBHCEtImz8oqXwtpnRBpxbT7GQq6AZAoFPLkmyCG9ChMG/2t5d bwwsKbp/BI46SYRydWNk2g/fxl45yMwt5G4nCjJMuSvpNCRziF7pTIPq2y3jFFVlf2 ntJ+GgKtYhHHlCfjZCvDjuuCMH33R6nZnaFhEyEM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726766AbfA1NVs (ORCPT ); Mon, 28 Jan 2019 08:21:48 -0500 Received: from mx2.suse.de ([195.135.220.15]:41968 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726647AbfA1NVs (ORCPT ); Mon, 28 Jan 2019 08:21:48 -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 BA9A4AF6F; Mon, 28 Jan 2019 13:21:46 +0000 (UTC) Date: Mon, 28 Jan 2019 14:21:46 +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: <20190128132146.GK18811@dhcp22.suse.cz> References: <20190128121609.9528-1-david@redhat.com> <20190128130709.GJ18811@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 14:14:28, 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. -- Michal Hocko SUSE Labs