From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753774AbcFPDmW (ORCPT ); Wed, 15 Jun 2016 23:42:22 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:38463 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753270AbcFPDmV (ORCPT ); Wed, 15 Jun 2016 23:42:21 -0400 X-IBM-Helo: d28dlp02.in.ibm.com X-IBM-MailFrom: khandual@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org Date: Thu, 16 Jun 2016 09:12:07 +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> <5760F970.7060805@linux.vnet.ibm.com> <20160616002617.GM17127@bbox> In-Reply-To: <20160616002617.GM17127@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: 16061603-0008-0000-0000-000002BF55BD X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16061603-0009-0000-0000-00000D96F7CD Message-Id: <5762200F.5040908@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-06-16_01:,, 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-1606160043 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/16/2016 05:56 AM, Minchan Kim wrote: > On Wed, Jun 15, 2016 at 12:15:04PM +0530, Anshuman Khandual wrote: >> 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. > > Thanks a lot! > >> >> 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 > > Hmm, page_add_file_rmap is not exported function. How does your driver can use it? Its not using the function directly, I just re-iterated the sequence of functions above. (do_set_pte -> page_add_file_rmap) gets called after we grab the page from driver through (__do_fault->vma->vm_ops->fault()). > Do you use vm_insert_pfn? > What type your vma is? VM_PFNMMAP or VM_MIXEDMAP? I dont use vm_insert_pfn(). Here is the sequence of events how the user space VMA gets the non LRU pages from the driver. - Driver registers a character device with 'struct file_operations' binding - Then the 'fops->mmap()' just binds the incoming 'struct vma' with a 'struct vm_operations_struct' which provides the 'vmops->fault()' routine which basically traps all page faults on the VMA and provides one page at a time through a driver specific allocation routine which hands over non LRU pages The VMA is not anything special as such. Its what we get when we try to do a simple mmap() on a file descriptor pointing to a character device. I can figure out all the VM_* flags it holds after creation. > > I want to make dummy driver to simulate your case. Sure. I hope the above mentioned steps will help you but in case you need more information, please do let me know. > It would be very helpful to implement/test pte-mapped non-lru page > migration feature. That's why I ask now. > >> 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 > > We could change __SetPageMovable doesn't need mapping argument. > Instead, it just marks PAGE_MAPPING_MOVABLE into page->mapping. > For that, user should take care of setting page->mapping earlier than > marking the flag. Sounds like a good idea, that way we dont loose the reverse mapping information. > >> 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 > We can set existing file->f_mapping under the page_lock. Thats another option along with what you mentioned above. > >> in there ? Sure, but then can we override file system generic ->isolate(), ->putback(), > > I don't get it. Why does it override file system generic functions? Sure it does not, it was just an wild idea to over come the problem.