From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f200.google.com (mail-pf0-f200.google.com [209.85.192.200]) by kanga.kvack.org (Postfix) with ESMTP id 92C276B0033 for ; Wed, 18 Oct 2017 22:47:34 -0400 (EDT) Received: by mail-pf0-f200.google.com with SMTP id y128so354530pfg.5 for ; Wed, 18 Oct 2017 19:47:34 -0700 (PDT) Received: from lgeamrelo12.lge.com (LGEAMRELO12.lge.com. [156.147.23.52]) by mx.google.com with ESMTP id x4si8445576plo.379.2017.10.18.19.47.32 for ; Wed, 18 Oct 2017 19:47:33 -0700 (PDT) Date: Thu, 19 Oct 2017 11:51:11 +0900 From: Joonsoo Kim Subject: Re: [PATCH 1/2] mm: drop migrate type checks from has_unmovable_pages Message-ID: <20171019025111.GA3852@js1304-P5Q-DELUXE> References: <20171013115835.zaehapuucuzl2vlv@dhcp22.suse.cz> <20171013120013.698-1-mhocko@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171013120013.698-1-mhocko@kernel.org> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: linux-mm@kvack.org, Michael Ellerman , Vlastimil Babka , Andrew Morton , KAMEZAWA Hiroyuki , Reza Arbab , Yasuaki Ishimatsu , qiuxishi@huawei.com, Igor Mammedov , Vitaly Kuznetsov , LKML , Michal Hocko On Fri, Oct 13, 2017 at 02:00:12PM +0200, Michal Hocko wrote: > From: Michal Hocko > > Michael has noticed that the memory offline tries to migrate kernel code > pages when doing > echo 0 > /sys/devices/system/memory/memory0/online > > The current implementation will fail the operation after several failed > page migration attempts but we shouldn't even attempt to migrate > that memory and fail right away because this memory is clearly not > migrateable. This will become a real problem when we drop the retry loop > counter resp. timeout. > > The real problem is in has_unmovable_pages in fact. We should fail if > there are any non migrateable pages in the area. In orther to guarantee > that remove the migrate type checks because MIGRATE_MOVABLE is not > guaranteed to contain only migrateable pages. It is merely a heuristic. > Similarly MIGRATE_CMA does guarantee that the page allocator doesn't > allocate any non-migrateable pages from the block but CMA allocations > themselves are unlikely to migrateable. Therefore remove both checks. Hello, This patch will break the CMA user. As you mentioned, CMA allocation itself isn't migrateable. So, after a single page is allocated through CMA allocation, has_unmovable_pages() will return true for this pageblock. Then, futher CMA allocation request to this pageblock will fail because it requires isolating the pageblock. Thanks. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org