From patchwork Wed Nov 14 21:16:59 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Hildenbrand X-Patchwork-Id: 10683097 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 032F51759 for ; Wed, 14 Nov 2018 21:17:30 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id E979F2B6B5 for ; Wed, 14 Nov 2018 21:17:29 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id DD6302B9C6; Wed, 14 Nov 2018 21:17:29 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 806662B90F for ; Wed, 14 Nov 2018 21:17:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728697AbeKOHWQ (ORCPT ); Thu, 15 Nov 2018 02:22:16 -0500 Received: from mx1.redhat.com ([209.132.183.28]:60974 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725756AbeKOHWP (ORCPT ); Thu, 15 Nov 2018 02:22:15 -0500 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id AA7332D814; Wed, 14 Nov 2018 21:17:23 +0000 (UTC) Received: from t460s.redhat.com (ovpn-116-99.ams2.redhat.com [10.36.116.99]) by smtp.corp.redhat.com (Postfix) with ESMTP id 578C761487; Wed, 14 Nov 2018 21:17:21 +0000 (UTC) From: David Hildenbrand To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, devel@linuxdriverproject.org, linux-fsdevel@vger.kernel.org, linux-pm@vger.kernel.org, xen-devel@lists.xenproject.org, David Hildenbrand , Andrew Morton , Matthew Wilcox , Michal Hocko , "Michael S. Tsirkin" Subject: [PATCH RFC 1/6] mm: balloon: update comment about isolation/migration/compaction Date: Wed, 14 Nov 2018 22:16:59 +0100 Message-Id: <20181114211704.6381-2-david@redhat.com> In-Reply-To: <20181114211704.6381-1-david@redhat.com> References: <20181114211704.6381-1-david@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Wed, 14 Nov 2018 21:17:23 +0000 (UTC) Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Commit b1123ea6d3b3 ("mm: balloon: use general non-lru movable page feature") reworked balloon handling to make use of the general non-lru movable page feature. The big comment block in balloon_compaction.h contains quite some outdated information. Let's fix this. Cc: Andrew Morton Cc: Matthew Wilcox Cc: Michal Hocko Cc: "Michael S. Tsirkin" Signed-off-by: David Hildenbrand --- include/linux/balloon_compaction.h | 26 +++++++++----------------- 1 file changed, 9 insertions(+), 17 deletions(-) diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h index 53051f3d8f25..cbe50da5a59d 100644 --- a/include/linux/balloon_compaction.h +++ b/include/linux/balloon_compaction.h @@ -4,15 +4,18 @@ * * Common interface definitions for making balloon pages movable by compaction. * - * Despite being perfectly possible to perform ballooned pages migration, they - * make a special corner case to compaction scans because balloon pages are not - * enlisted at any LRU list like the other pages we do compact / migrate. + * Balloon page migration makes use of the general non-lru movable page + * feature. + * + * page->private is used to reference the responsible balloon device. + * page->mapping is used in context of non-lru page migration to reference + * the address space operations for page isolation/migration/compaction. * * As the page isolation scanning step a compaction thread does is a lockless * procedure (from a page standpoint), it might bring some racy situations while * performing balloon page compaction. In order to sort out these racy scenarios * and safely perform balloon's page compaction and migration we must, always, - * ensure following these three simple rules: + * ensure following these simple rules: * * i. when updating a balloon's page ->mapping element, strictly do it under * the following lock order, independently of the far superior @@ -21,19 +24,8 @@ * +--spin_lock_irq(&b_dev_info->pages_lock); * ... page->mapping updates here ... * - * ii. before isolating or dequeueing a balloon page from the balloon device - * pages list, the page reference counter must be raised by one and the - * extra refcount must be dropped when the page is enqueued back into - * the balloon device page list, thus a balloon page keeps its reference - * counter raised only while it is under our special handling; - * - * iii. after the lockless scan step have selected a potential balloon page for - * isolation, re-test the PageBalloon mark and the PagePrivate flag - * under the proper page lock, to ensure isolating a valid balloon page - * (not yet isolated, nor under release procedure) - * - * iv. isolation or dequeueing procedure must clear PagePrivate flag under - * page lock together with removing page from balloon device page list. + * ii. isolation or dequeueing procedure must remove the page from balloon + * device page list under b_dev_info->pages_lock. * * The functions provided by this interface are placed to help on coping with * the aforementioned balloon page corner case, as well as to ensure the simple