On 06/28/2016 12:09 PM, Minchan Kim wrote: > 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 I really appreciate. Was just curious about the problem and any potential solution we can look into. > after soft landing of current non-lru-no-mapped page migration to solve > current real field issues. yeah it makes sense. > > 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; > } > Okay. > 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. Okay and the above test_set_page_dirty() example is sufficient ? > > 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. Got it, so what changes you did ? Implemented PG_isolated differently not by overriding PG_reclaim or something else ? Yes set_page_dirty indeed clears the PG_reclaim flag. > > With that, it seems to work. But I'm not saying it's right model now So the mapped pages migration was successful ? Even after overloading filp->f_mapping->a_ops = &test_aops, we still have the RMAP information intact with filp->f_mappinp pointed interval tree. But would really like to see the code changes. > for device drivers. In runtime, replacing filp->f_mapping->a_ops with > custom a_ops of own driver seems to be hacky to me. Yeah I thought so. > 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. I will look into these details. > 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. Sure, makes sense. Mean while it will be really great if you could share your code changes as described above, so that I can try them out. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>