From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk1-f197.google.com (mail-qk1-f197.google.com [209.85.222.197]) by kanga.kvack.org (Postfix) with ESMTP id AB0F16B0005 for ; Wed, 14 Nov 2018 16:17:25 -0500 (EST) Received: by mail-qk1-f197.google.com with SMTP id h68so40836021qke.3 for ; Wed, 14 Nov 2018 13:17:25 -0800 (PST) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id v11si1033342qvj.128.2018.11.14.13.17.24 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 14 Nov 2018 13:17:24 -0800 (PST) From: David Hildenbrand 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> Sender: owner-linux-mm@kvack.org List-ID: 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" 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 The big comment block in balloon_compaction.h contains quite some outdated information.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 -- 2.17.2