From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752528AbcF1GjA (ORCPT ); Tue, 28 Jun 2016 02:39:00 -0400 Received: from LGEAMRELO11.lge.com ([156.147.23.51]:42188 "EHLO lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752516AbcF1Gi4 (ORCPT ); Tue, 28 Jun 2016 02:38:56 -0400 X-Original-SENDERIP: 156.147.1.125 X-Original-MAILFROM: minchan@kernel.org X-Original-SENDERIP: 10.177.223.161 X-Original-MAILFROM: minchan@kernel.org Date: Tue, 28 Jun 2016 15:39:12 +0900 From: Minchan Kim To: Anshuman Khandual 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 Message-ID: <20160628063912.GA25560@bbox> References: <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> <5762200F.5040908@linux.vnet.ibm.com> <20160616053754.GQ17127@bbox> <5770BEC5.3010807@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5770BEC5.3010807@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 27, 2016 at 11:21:01AM +0530, Anshuman Khandual wrote: > On 06/16/2016 11:07 AM, Minchan Kim wrote: > > On Thu, Jun 16, 2016 at 09:12:07AM +0530, Anshuman Khandual wrote: > >> 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. > > > > I got understood now. :) > > I will test it with dummy driver and will Cc'ed when I send a patch. > > Hello Minchan, > > Do you have any updates on this ? The V7 of the series still has this limitation. > Did you get a chance to test the driver out ? I am still concerned about how to > handle the struct address_space override problem within the struct page. Hi Anshuman, Slow but I am working on that. :) However, as I said, I want to do it after soft landing of current non-lru-no-mapped page migration to solve current real field issues. About the overriding problem of non-lru-mapped-page, I implemented dummy driver as miscellaneous device and in test_mmap(file_operations.mmap), I changed a_ops with my address_space_operations. int test_mmap(struct file *filp, struct vm_area_struct *vma) { filp->f_mapping->a_ops = &test_aops; vma->vm_ops = &test_vm_ops; vma->vm_private_data = filp->private_data; return 0; } test_aops should have *set_page_dirty* overriding. static int test_set_pag_dirty(struct page *page) { if (!PageDirty(page)) SetPageDirty*page); return 0; } Otherwise, it goes BUG_ON during radix tree operation because currently try_to_unmap is designed for file-lru pages which lives in page cache so it propagates page table dirty bit to PG_dirty flag of struct page by set_page_dirty. And set_page_dirty want to mark dirty tag in radix tree node but it's character driver so the page cache doesn't have it. That's why we encounter BUG_ON in radix tree operation. Anyway, to test, I implemented set_page_dirty in my dummy driver. With only that, it doesn't work because I need to modify migrate.c to work non-lru-mapped-page and changing PG_isolated flag which is override of PG_reclaim which is cleared in set_page_dirty. With that, it seems to work. But I'm not saying it's right model now for device drivers. In runtime, replacing filp->f_mapping->a_ops with custom a_ops of own driver seems to be hacky to me. So, I'm considering now new pseudo fs "movable_inode" which will support struct file *movable_inode_getfile(const char *name, const struct file_operations *fop, const struct address_space_operations *a_ops) { struct path path; struct qstr this; struct inode *inode; struct super_block *sb; this.name = name; this.len = strlen(name); this.hash = 0; sb = movable_mnt.mnt_sb; patch.denty = d_alloc_pseudo(movable_inode_mnt->mnt_sb, &this); patch.mnt = mntget(movable_inode_mnt); inode = new_inode(sb); .. .. inode->i_mapping->a_ops = a_ops; d_instantiate(path.dentry, inode); return alloc_file(&path, FMODE_WRITE | FMODE_READ, f_op); } And in our driver, we can change vma->vm_file with new one. int test_mmap(struct file *filp, struct vm_area_structd *vma) { struct file *newfile = movable_inode_getfile("[test"], filep->f_op, &test_aops); vma->vm_file = newfile; .. .. } When I read mmap_region in mm/mmap.c, it's reasonable usecase which dirver's mmap changes vma->vm_file with own file. Anyway, it needs many subtle changes in mm/vfs/driver side so need to review from each maintainers related subsystem so I want to not be hurry. Thanks. > > - Anshuman >