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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 34BE9C6778F for ; Thu, 26 Jul 2018 19:50:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E645A2088E for ; Thu, 26 Jul 2018 19:50:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E645A2088E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731719AbeGZVIg (ORCPT ); Thu, 26 Jul 2018 17:08:36 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:40600 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731629AbeGZVIg (ORCPT ); Thu, 26 Jul 2018 17:08:36 -0400 Received: from akpm3.svl.corp.google.com (unknown [104.133.9.92]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 2F996CEE; Thu, 26 Jul 2018 19:50:14 +0000 (UTC) Date: Thu, 26 Jul 2018 12:50:13 -0700 From: Andrew Morton To: David Hildenbrand Cc: Michal Hocko , Vlastimil Babka , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Baoquan He , Dave Young , Greg Kroah-Hartman , Hari Bathini , Huang Ying , "Kirill A. Shutemov" , =?ISO-8859-1?Q?Marc-Andr=E9?= Lureau , Matthew Wilcox , Miles Chen , Pavel Tatashin , Petr Tesarik Subject: Re: [PATCH v1 0/2] mm/kdump: exclude reserved pages in dumps Message-Id: <20180726125013.ea82bfa3194386733b3943ab@linux-foundation.org> In-Reply-To: <21c31952-7632-b8e1-aa33-d124ce96b88e@redhat.com> References: <20180720123422.10127-1-david@redhat.com> <9f46f0ed-e34c-73be-60ca-c892fb19ed08@suse.cz> <20180724072237.GA28386@dhcp22.suse.cz> <20180726083042.GC28386@dhcp22.suse.cz> <21c31952-7632-b8e1-aa33-d124ce96b88e@redhat.com> X-Mailer: Sylpheed 3.6.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 26 Jul 2018 10:45:54 +0200 David Hildenbrand wrote: > > Does each user of PG_balloon check for PG_reserved? If this is the case > > then yes this would be OK. > > > > I can only spot one user of PageBalloon() at all (fs/proc/page.c) , > which makes me wonder if this bit is actually still relevant. I think > the last "real" user was removed with > > commit b1123ea6d3b3da25af5c8a9d843bd07ab63213f4 > Author: Minchan Kim > Date: Tue Jul 26 15:23:09 2016 -0700 > > mm: balloon: use general non-lru movable page feature > > Now, VM has a feature to migrate non-lru movable pages so balloon > doesn't need custom migration hooks in migrate.c and compaction.c. > > > The only user of PG_balloon in general is > "include/linux/balloon_compaction.h", used effectively only by > virtio_balloon. > > All such pages are allocated via balloon_page_alloc() and never set > reserved. > > So to me it looks like PG_balloon could be easily reused, especially to > also exclude virtio-balloon pages from dumps. Agree. Maintaining a thingy for page-types.c which hardly anyone uses (surely) isn't sufficient justification for consuming a page flag. We should check with the virtio developers first, but this does seem to be begging to be reclaimed.