From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752367AbcFOGpU (ORCPT ); Wed, 15 Jun 2016 02:45:20 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:45316 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751406AbcFOGpS (ORCPT ); Wed, 15 Jun 2016 02:45:18 -0400 X-IBM-Helo: d23dlp02.au.ibm.com X-IBM-MailFrom: khandual@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org Date: Wed, 15 Jun 2016 12:15:04 +0530 From: Anshuman Khandual User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Minchan Kim CC: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Rik van Riel , Vlastimil Babka , Joonsoo Kim , Mel Gorman , Hugh Dickins , Rafael Aquini , virtualization@lists.linux-foundation.org, Jonathan Corbet , John Einar Reitan , dri-devel@lists.freedesktop.org, Sergey Senozhatsky , Gioh Kim Subject: Re: [PATCH v6v3 02/12] mm: migrate: support non-lru movable page migration References: <1463754225-31311-1-git-send-email-minchan@kernel.org> <1463754225-31311-3-git-send-email-minchan@kernel.org> <20160530013926.GB8683@bbox> <20160531000117.GB18314@bbox> <575E7F0B.8010201@linux.vnet.ibm.com> <20160615023249.GG17127@bbox> In-Reply-To: <20160615023249.GG17127@bbox> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16061506-0044-0000-0000-000001B48A0E X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16061506-0045-0000-0000-000004EE8221 Message-Id: <5760F970.7060805@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-06-15_04:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1604210000 definitions=main-1606150075 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/15/2016 08:02 AM, Minchan Kim wrote: > Hi, > > On Mon, Jun 13, 2016 at 03:08:19PM +0530, Anshuman Khandual wrote: >> > On 05/31/2016 05:31 AM, Minchan Kim wrote: >>> > > @@ -791,6 +921,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage, >>> > > int rc = -EAGAIN; >>> > > int page_was_mapped = 0; >>> > > struct anon_vma *anon_vma = NULL; >>> > > + bool is_lru = !__PageMovable(page); >>> > > >>> > > if (!trylock_page(page)) { >>> > > if (!force || mode == MIGRATE_ASYNC) >>> > > @@ -871,6 +1002,11 @@ static int __unmap_and_move(struct page *page, struct page *newpage, >>> > > goto out_unlock_both; >>> > > } >>> > > >>> > > + if (unlikely(!is_lru)) { >>> > > + rc = move_to_new_page(newpage, page, mode); >>> > > + goto out_unlock_both; >>> > > + } >>> > > + >> > >> > Hello Minchan, >> > >> > I might be missing something here but does this implementation support the >> > scenario where these non LRU pages owned by the driver mapped as PTE into >> > process page table ? Because the "goto out_unlock_both" statement above >> > skips all the PTE unmap, putting a migration PTE and removing the migration >> > PTE steps. > You're right. Unfortunately, it doesn't support right now but surely, > it's my TODO after landing this work. > > Could you share your usecase? Sure. My driver has privately managed non LRU pages which gets mapped into user space process page table through f_ops->mmap() and vmops->fault() which then updates the file RMAP (page->mapping->i_mmap) through page_add_file_rmap(page). One thing to note here is that the page->mapping eventually points to struct address_space (file->f_mapping) which belongs to the character device file (created using mknod) which we are using for establishing the mmap() regions in the user space. Now as per this new framework, all the page's are to be made __SetPageMovable before passing the list down to migrate_pages(). Now __SetPageMovable() takes *new* struct address_space as an argument and replaces the existing page->mapping. Now thats the problem, we have lost all our connection to the existing file RMAP information. This stands as a problem when we try to migrate these non LRU pages which are PTE mapped. The rmap_walk_file() never finds them in the VMA, skips all the migrate PTE steps and then the migration eventually fails. Seems like assigning a new struct address_space to the page through __SetPageMovable() is the source of the problem. Can it take the existing (file->f_mapping) as an argument in there ? Sure, but then can we override file system generic ->isolate(), ->putback(), ->migratepages() functions ? I dont think so. I am sure, there must be some work around to fix this problem for the driver. But we need to rethink this framework from supporting these mapped non LRU pages point of view. I might be missing something here, feel free to point out. - Anshuman