2 * Memory Migration functionality - linux/mm/migration.c
4 * Copyright (C) 2006 Silicon Graphics, Inc., Christoph Lameter
6 * Page migration was first developed in the context of the memory hotplug
7 * project. The main authors of the migration code are:
9 * IWAMOTO Toshihiro <iwamoto@valinux.co.jp>
10 * Hirokazu Takahashi <taka@valinux.co.jp>
11 * Dave Hansen <haveblue@us.ibm.com>
15 #include <linux/migrate.h>
16 #include <linux/module.h>
17 #include <linux/swap.h>
18 #include <linux/swapops.h>
19 #include <linux/pagemap.h>
20 #include <linux/buffer_head.h>
21 #include <linux/mm_inline.h>
22 #include <linux/nsproxy.h>
23 #include <linux/pagevec.h>
24 #include <linux/rmap.h>
25 #include <linux/topology.h>
26 #include <linux/cpu.h>
27 #include <linux/cpuset.h>
28 #include <linux/writeback.h>
29 #include <linux/mempolicy.h>
30 #include <linux/vmalloc.h>
31 #include <linux/security.h>
32 #include <linux/memcontrol.h>
33 #include <linux/syscalls.h>
37 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
40 * migrate_prep() needs to be called before we start compiling a list of pages
41 * to be migrated using isolate_lru_page().
43 int migrate_prep(void)
46 * Clear the LRU lists so pages can be isolated.
47 * Note that pages may be moved off the LRU after we have
48 * drained them. Those pages will fail to migrate like other
49 * pages that may be busy.
57 * Add isolated pages on the list back to the LRU under page lock
58 * to avoid leaking evictable pages back onto unevictable list.
60 * returns the number of pages put back.
62 int putback_lru_pages(struct list_head *l)
68 list_for_each_entry_safe(page, page2, l, lru) {
70 dec_zone_page_state(page, NR_ISOLATED_ANON +
71 page_is_file_cache(page));
72 putback_lru_page(page);
79 * Restore a potential migration pte to a working pte entry
81 static void remove_migration_pte(struct vm_area_struct *vma,
82 struct page *old, struct page *new)
84 struct mm_struct *mm = vma->vm_mm;
91 unsigned long addr = page_address_in_vma(new, vma);
96 pgd = pgd_offset(mm, addr);
97 if (!pgd_present(*pgd))
100 pud = pud_offset(pgd, addr);
101 if (!pud_present(*pud))
104 pmd = pmd_offset(pud, addr);
105 if (!pmd_present(*pmd))
108 ptep = pte_offset_map(pmd, addr);
110 if (!is_swap_pte(*ptep)) {
115 ptl = pte_lockptr(mm, pmd);
118 if (!is_swap_pte(pte))
121 entry = pte_to_swp_entry(pte);
123 if (!is_migration_entry(entry) || migration_entry_to_page(entry) != old)
127 pte = pte_mkold(mk_pte(new, vma->vm_page_prot));
128 if (is_write_migration_entry(entry))
129 pte = pte_mkwrite(pte);
130 flush_cache_page(vma, addr, pte_pfn(pte));
131 set_pte_at(mm, addr, ptep, pte);
134 page_add_anon_rmap(new, vma, addr);
136 page_add_file_rmap(new);
138 /* No need to invalidate - it was non-present before */
139 update_mmu_cache(vma, addr, pte);
142 pte_unmap_unlock(ptep, ptl);
146 * Note that remove_file_migration_ptes will only work on regular mappings,
147 * Nonlinear mappings do not use migration entries.
149 static void remove_file_migration_ptes(struct page *old, struct page *new)
151 struct vm_area_struct *vma;
152 struct address_space *mapping = new->mapping;
153 struct prio_tree_iter iter;
154 pgoff_t pgoff = new->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
159 spin_lock(&mapping->i_mmap_lock);
161 vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff)
162 remove_migration_pte(vma, old, new);
164 spin_unlock(&mapping->i_mmap_lock);
168 * Must hold mmap_sem lock on at least one of the vmas containing
169 * the page so that the anon_vma cannot vanish.
171 static void remove_anon_migration_ptes(struct page *old, struct page *new)
173 struct anon_vma *anon_vma;
174 struct vm_area_struct *vma;
175 unsigned long mapping;
177 mapping = (unsigned long)new->mapping;
179 if (!mapping || (mapping & PAGE_MAPPING_ANON) == 0)
183 * We hold the mmap_sem lock. So no need to call page_lock_anon_vma.
185 anon_vma = (struct anon_vma *) (mapping - PAGE_MAPPING_ANON);
186 spin_lock(&anon_vma->lock);
188 list_for_each_entry(vma, &anon_vma->head, anon_vma_node)
189 remove_migration_pte(vma, old, new);
191 spin_unlock(&anon_vma->lock);
195 * Get rid of all migration entries and replace them by
196 * references to the indicated page.
198 static void remove_migration_ptes(struct page *old, struct page *new)
201 remove_anon_migration_ptes(old, new);
203 remove_file_migration_ptes(old, new);
207 * Something used the pte of a page under migration. We need to
208 * get to the page and wait until migration is finished.
209 * When we return from this function the fault will be retried.
211 * This function is called from do_swap_page().
213 void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
214 unsigned long address)
221 ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
223 if (!is_swap_pte(pte))
226 entry = pte_to_swp_entry(pte);
227 if (!is_migration_entry(entry))
230 page = migration_entry_to_page(entry);
233 * Once radix-tree replacement of page migration started, page_count
234 * *must* be zero. And, we don't want to call wait_on_page_locked()
235 * against a page without get_page().
236 * So, we use get_page_unless_zero(), here. Even failed, page fault
239 if (!get_page_unless_zero(page))
241 pte_unmap_unlock(ptep, ptl);
242 wait_on_page_locked(page);
246 pte_unmap_unlock(ptep, ptl);
250 * Replace the page in the mapping.
252 * The number of remaining references must be:
253 * 1 for anonymous pages without a mapping
254 * 2 for pages with a mapping
255 * 3 for pages with a mapping and PagePrivate/PagePrivate2 set.
257 static int migrate_page_move_mapping(struct address_space *mapping,
258 struct page *newpage, struct page *page)
264 /* Anonymous page without mapping */
265 if (page_count(page) != 1)
270 spin_lock_irq(&mapping->tree_lock);
272 pslot = radix_tree_lookup_slot(&mapping->page_tree,
275 expected_count = 2 + page_has_private(page);
276 if (page_count(page) != expected_count ||
277 (struct page *)radix_tree_deref_slot(pslot) != page) {
278 spin_unlock_irq(&mapping->tree_lock);
282 if (!page_freeze_refs(page, expected_count)) {
283 spin_unlock_irq(&mapping->tree_lock);
288 * Now we know that no one else is looking at the page.
290 get_page(newpage); /* add cache reference */
291 if (PageSwapCache(page)) {
292 SetPageSwapCache(newpage);
293 set_page_private(newpage, page_private(page));
296 radix_tree_replace_slot(pslot, newpage);
298 page_unfreeze_refs(page, expected_count);
300 * Drop cache reference from old page.
301 * We know this isn't the last reference.
306 * If moved to a different zone then also account
307 * the page for that zone. Other VM counters will be
308 * taken care of when we establish references to the
309 * new page and drop references to the old page.
311 * Note that anonymous pages are accounted for
312 * via NR_FILE_PAGES and NR_ANON_PAGES if they
313 * are mapped to swap space.
315 __dec_zone_page_state(page, NR_FILE_PAGES);
316 __inc_zone_page_state(newpage, NR_FILE_PAGES);
317 if (PageSwapBacked(page)) {
318 __dec_zone_page_state(page, NR_SHMEM);
319 __inc_zone_page_state(newpage, NR_SHMEM);
321 spin_unlock_irq(&mapping->tree_lock);
327 * Copy the page to its new location
329 static void migrate_page_copy(struct page *newpage, struct page *page)
333 copy_highpage(newpage, page);
336 SetPageError(newpage);
337 if (PageReferenced(page))
338 SetPageReferenced(newpage);
339 if (PageUptodate(page))
340 SetPageUptodate(newpage);
341 if (TestClearPageActive(page)) {
342 VM_BUG_ON(PageUnevictable(page));
343 SetPageActive(newpage);
345 unevictable_migrate_page(newpage, page);
346 if (PageChecked(page))
347 SetPageChecked(newpage);
348 if (PageMappedToDisk(page))
349 SetPageMappedToDisk(newpage);
351 if (PageDirty(page)) {
352 clear_page_dirty_for_io(page);
354 * Want to mark the page and the radix tree as dirty, and
355 * redo the accounting that clear_page_dirty_for_io undid,
356 * but we can't use set_page_dirty because that function
357 * is actually a signal that all of the page has become dirty.
358 * Wheras only part of our page may be dirty.
360 __set_page_dirty_nobuffers(newpage);
363 mlock_migrate_page(newpage, page);
365 ClearPageSwapCache(page);
366 ClearPagePrivate(page);
367 set_page_private(page, 0);
368 /* page->mapping contains a flag for PageAnon() */
369 anon = PageAnon(page);
370 page->mapping = NULL;
373 * If any waiters have accumulated on the new page then
376 if (PageWriteback(newpage))
377 end_page_writeback(newpage);
380 /************************************************************
381 * Migration functions
382 ***********************************************************/
384 /* Always fail migration. Used for mappings that are not movable */
385 int fail_migrate_page(struct address_space *mapping,
386 struct page *newpage, struct page *page)
390 EXPORT_SYMBOL(fail_migrate_page);
393 * Common logic to directly migrate a single page suitable for
394 * pages that do not use PagePrivate/PagePrivate2.
396 * Pages are locked upon entry and exit.
398 int migrate_page(struct address_space *mapping,
399 struct page *newpage, struct page *page)
403 BUG_ON(PageWriteback(page)); /* Writeback must be complete */
405 rc = migrate_page_move_mapping(mapping, newpage, page);
410 migrate_page_copy(newpage, page);
413 EXPORT_SYMBOL(migrate_page);
417 * Migration function for pages with buffers. This function can only be used
418 * if the underlying filesystem guarantees that no other references to "page"
421 int buffer_migrate_page(struct address_space *mapping,
422 struct page *newpage, struct page *page)
424 struct buffer_head *bh, *head;
427 if (!page_has_buffers(page))
428 return migrate_page(mapping, newpage, page);
430 head = page_buffers(page);
432 rc = migrate_page_move_mapping(mapping, newpage, page);
441 bh = bh->b_this_page;
443 } while (bh != head);
445 ClearPagePrivate(page);
446 set_page_private(newpage, page_private(page));
447 set_page_private(page, 0);
453 set_bh_page(bh, newpage, bh_offset(bh));
454 bh = bh->b_this_page;
456 } while (bh != head);
458 SetPagePrivate(newpage);
460 migrate_page_copy(newpage, page);
466 bh = bh->b_this_page;
468 } while (bh != head);
472 EXPORT_SYMBOL(buffer_migrate_page);
476 * Writeback a page to clean the dirty state
478 static int writeout(struct address_space *mapping, struct page *page)
480 struct writeback_control wbc = {
481 .sync_mode = WB_SYNC_NONE,
484 .range_end = LLONG_MAX,
490 if (!mapping->a_ops->writepage)
491 /* No write method for the address space */
494 if (!clear_page_dirty_for_io(page))
495 /* Someone else already triggered a write */
499 * A dirty page may imply that the underlying filesystem has
500 * the page on some queue. So the page must be clean for
501 * migration. Writeout may mean we loose the lock and the
502 * page state is no longer what we checked for earlier.
503 * At this point we know that the migration attempt cannot
506 remove_migration_ptes(page, page);
508 rc = mapping->a_ops->writepage(page, &wbc);
510 if (rc != AOP_WRITEPAGE_ACTIVATE)
511 /* unlocked. Relock */
514 return (rc < 0) ? -EIO : -EAGAIN;
518 * Default handling if a filesystem does not provide a migration function.
520 static int fallback_migrate_page(struct address_space *mapping,
521 struct page *newpage, struct page *page)
524 return writeout(mapping, page);
527 * Buffers may be managed in a filesystem specific way.
528 * We must have no buffers or drop them.
530 if (page_has_private(page) &&
531 !try_to_release_page(page, GFP_KERNEL))
534 return migrate_page(mapping, newpage, page);
538 * Move a page to a newly allocated page
539 * The page is locked and all ptes have been successfully removed.
541 * The new page will have replaced the old page if this function
548 static int move_to_new_page(struct page *newpage, struct page *page)
550 struct address_space *mapping;
554 * Block others from accessing the page when we get around to
555 * establishing additional references. We are the only one
556 * holding a reference to the new page at this point.
558 if (!trylock_page(newpage))
561 /* Prepare mapping for the new page.*/
562 newpage->index = page->index;
563 newpage->mapping = page->mapping;
564 if (PageSwapBacked(page))
565 SetPageSwapBacked(newpage);
567 mapping = page_mapping(page);
569 rc = migrate_page(mapping, newpage, page);
570 else if (mapping->a_ops->migratepage)
572 * Most pages have a mapping and most filesystems
573 * should provide a migration function. Anonymous
574 * pages are part of swap space which also has its
575 * own migration function. This is the most common
576 * path for page migration.
578 rc = mapping->a_ops->migratepage(mapping,
581 rc = fallback_migrate_page(mapping, newpage, page);
584 remove_migration_ptes(page, newpage);
586 newpage->mapping = NULL;
588 unlock_page(newpage);
594 * Obtain the lock on page, remove all ptes and migrate the page
595 * to the newly allocated page in newpage.
597 static int unmap_and_move(new_page_t get_new_page, unsigned long private,
598 struct page *page, int force)
602 struct page *newpage = get_new_page(page, private, &result);
605 struct mem_cgroup *mem;
610 if (page_count(page) == 1) {
611 /* page was freed from under us. So we are done. */
615 /* prepare cgroup just returns 0 or -ENOMEM */
618 if (!trylock_page(page)) {
624 /* charge against new page */
625 charge = mem_cgroup_prepare_migration(page, &mem);
626 if (charge == -ENOMEM) {
632 if (PageWriteback(page)) {
635 wait_on_page_writeback(page);
638 * By try_to_unmap(), page->mapcount goes down to 0 here. In this case,
639 * we cannot notice that anon_vma is freed while we migrates a page.
640 * This rcu_read_lock() delays freeing anon_vma pointer until the end
641 * of migration. File cache pages are no problem because of page_lock()
642 * File Caches may use write_page() or lock_page() in migration, then,
643 * just care Anon page here.
645 if (PageAnon(page)) {
651 * Corner case handling:
652 * 1. When a new swap-cache page is read into, it is added to the LRU
653 * and treated as swapcache but it has no rmap yet.
654 * Calling try_to_unmap() against a page->mapping==NULL page will
655 * trigger a BUG. So handle it here.
656 * 2. An orphaned page (see truncate_complete_page) might have
657 * fs-private metadata. The page can be picked up due to memory
658 * offlining. Everywhere else except page reclaim, the page is
659 * invisible to the vm, so the page can not be migrated. So try to
660 * free the metadata, so the page can be freed.
662 if (!page->mapping) {
663 if (!PageAnon(page) && page_has_private(page)) {
665 * Go direct to try_to_free_buffers() here because
666 * a) that's what try_to_release_page() would do anyway
667 * b) we may be under rcu_read_lock() here, so we can't
668 * use GFP_KERNEL which is what try_to_release_page()
669 * needs to be effective.
671 try_to_free_buffers(page);
677 /* Establish migration ptes or remove ptes */
678 try_to_unmap(page, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
681 if (!page_mapped(page))
682 rc = move_to_new_page(newpage, page);
685 remove_migration_ptes(page, page);
691 mem_cgroup_end_migration(mem, page, newpage);
697 * A page that has been migrated has all references
698 * removed and will be freed. A page that has not been
699 * migrated will have kepts its references and be
702 list_del(&page->lru);
703 dec_zone_page_state(page, NR_ISOLATED_ANON +
704 page_is_file_cache(page));
705 putback_lru_page(page);
711 * Move the new page to the LRU. If migration was not successful
712 * then this will free the page.
714 putback_lru_page(newpage);
720 *result = page_to_nid(newpage);
728 * The function takes one list of pages to migrate and a function
729 * that determines from the page to be migrated and the private data
730 * the target of the move and allocates the page.
732 * The function returns after 10 attempts or if no pages
733 * are movable anymore because to has become empty
734 * or no retryable pages exist anymore. All pages will be
735 * returned to the LRU or freed.
737 * Return: Number of pages not migrated or error code.
739 int migrate_pages(struct list_head *from,
740 new_page_t get_new_page, unsigned long private)
747 int swapwrite = current->flags & PF_SWAPWRITE;
751 local_irq_save(flags);
752 list_for_each_entry(page, from, lru)
753 __inc_zone_page_state(page, NR_ISOLATED_ANON +
754 page_is_file_cache(page));
755 local_irq_restore(flags);
758 current->flags |= PF_SWAPWRITE;
760 for(pass = 0; pass < 10 && retry; pass++) {
763 list_for_each_entry_safe(page, page2, from, lru) {
766 rc = unmap_and_move(get_new_page, private,
778 /* Permanent failure */
787 current->flags &= ~PF_SWAPWRITE;
789 putback_lru_pages(from);
794 return nr_failed + retry;
799 * Move a list of individual pages
801 struct page_to_node {
808 static struct page *new_page_node(struct page *p, unsigned long private,
811 struct page_to_node *pm = (struct page_to_node *)private;
813 while (pm->node != MAX_NUMNODES && pm->page != p)
816 if (pm->node == MAX_NUMNODES)
819 *result = &pm->status;
821 return alloc_pages_exact_node(pm->node,
822 GFP_HIGHUSER_MOVABLE | GFP_THISNODE, 0);
826 * Move a set of pages as indicated in the pm array. The addr
827 * field must be set to the virtual address of the page to be moved
828 * and the node number must contain a valid target node.
829 * The pm array ends with node = MAX_NUMNODES.
831 static int do_move_page_to_node_array(struct mm_struct *mm,
832 struct page_to_node *pm,
836 struct page_to_node *pp;
839 down_read(&mm->mmap_sem);
842 * Build a list of pages to migrate
844 for (pp = pm; pp->node != MAX_NUMNODES; pp++) {
845 struct vm_area_struct *vma;
849 vma = find_vma(mm, pp->addr);
850 if (!vma || !vma_migratable(vma))
853 page = follow_page(vma, pp->addr, FOLL_GET);
863 if (PageReserved(page)) /* Check for zero page */
867 err = page_to_nid(page);
871 * Node already in the right place
876 if (page_mapcount(page) > 1 &&
880 err = isolate_lru_page(page);
882 list_add_tail(&page->lru, &pagelist);
885 * Either remove the duplicate refcount from
886 * isolate_lru_page() or drop the page ref if it was
895 if (!list_empty(&pagelist))
896 err = migrate_pages(&pagelist, new_page_node,
899 up_read(&mm->mmap_sem);
904 * Migrate an array of page address onto an array of nodes and fill
905 * the corresponding array of status.
907 static int do_pages_move(struct mm_struct *mm, struct task_struct *task,
908 unsigned long nr_pages,
909 const void __user * __user *pages,
910 const int __user *nodes,
911 int __user *status, int flags)
913 struct page_to_node *pm;
914 nodemask_t task_nodes;
915 unsigned long chunk_nr_pages;
916 unsigned long chunk_start;
919 task_nodes = cpuset_mems_allowed(task);
922 pm = (struct page_to_node *)__get_free_page(GFP_KERNEL);
929 * Store a chunk of page_to_node array in a page,
930 * but keep the last one as a marker
932 chunk_nr_pages = (PAGE_SIZE / sizeof(struct page_to_node)) - 1;
934 for (chunk_start = 0;
935 chunk_start < nr_pages;
936 chunk_start += chunk_nr_pages) {
939 if (chunk_start + chunk_nr_pages > nr_pages)
940 chunk_nr_pages = nr_pages - chunk_start;
942 /* fill the chunk pm with addrs and nodes from user-space */
943 for (j = 0; j < chunk_nr_pages; j++) {
944 const void __user *p;
948 if (get_user(p, pages + j + chunk_start))
950 pm[j].addr = (unsigned long) p;
952 if (get_user(node, nodes + j + chunk_start))
956 if (!node_state(node, N_HIGH_MEMORY))
960 if (!node_isset(node, task_nodes))
966 /* End marker for this chunk */
967 pm[chunk_nr_pages].node = MAX_NUMNODES;
969 /* Migrate this chunk */
970 err = do_move_page_to_node_array(mm, pm,
971 flags & MPOL_MF_MOVE_ALL);
975 /* Return status information */
976 for (j = 0; j < chunk_nr_pages; j++)
977 if (put_user(pm[j].status, status + j + chunk_start)) {
985 free_page((unsigned long)pm);
991 * Determine the nodes of an array of pages and store it in an array of status.
993 static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
994 const void __user **pages, int *status)
998 down_read(&mm->mmap_sem);
1000 for (i = 0; i < nr_pages; i++) {
1001 unsigned long addr = (unsigned long)(*pages);
1002 struct vm_area_struct *vma;
1006 vma = find_vma(mm, addr);
1010 page = follow_page(vma, addr, 0);
1012 err = PTR_ERR(page);
1017 /* Use PageReserved to check for zero page */
1018 if (!page || PageReserved(page))
1021 err = page_to_nid(page);
1029 up_read(&mm->mmap_sem);
1033 * Determine the nodes of a user array of pages and store it in
1034 * a user array of status.
1036 static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages,
1037 const void __user * __user *pages,
1040 #define DO_PAGES_STAT_CHUNK_NR 16
1041 const void __user *chunk_pages[DO_PAGES_STAT_CHUNK_NR];
1042 int chunk_status[DO_PAGES_STAT_CHUNK_NR];
1043 unsigned long i, chunk_nr = DO_PAGES_STAT_CHUNK_NR;
1046 for (i = 0; i < nr_pages; i += chunk_nr) {
1047 if (chunk_nr + i > nr_pages)
1048 chunk_nr = nr_pages - i;
1050 err = copy_from_user(chunk_pages, &pages[i],
1051 chunk_nr * sizeof(*chunk_pages));
1057 do_pages_stat_array(mm, chunk_nr, chunk_pages, chunk_status);
1059 err = copy_to_user(&status[i], chunk_status,
1060 chunk_nr * sizeof(*chunk_status));
1073 * Move a list of pages in the address space of the currently executing
1076 SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
1077 const void __user * __user *, pages,
1078 const int __user *, nodes,
1079 int __user *, status, int, flags)
1081 const struct cred *cred = current_cred(), *tcred;
1082 struct task_struct *task;
1083 struct mm_struct *mm;
1087 if (flags & ~(MPOL_MF_MOVE|MPOL_MF_MOVE_ALL))
1090 if ((flags & MPOL_MF_MOVE_ALL) && !capable(CAP_SYS_NICE))
1093 /* Find the mm_struct */
1094 read_lock(&tasklist_lock);
1095 task = pid ? find_task_by_vpid(pid) : current;
1097 read_unlock(&tasklist_lock);
1100 mm = get_task_mm(task);
1101 read_unlock(&tasklist_lock);
1107 * Check if this process has the right to modify the specified
1108 * process. The right exists if the process has administrative
1109 * capabilities, superuser privileges or the same
1110 * userid as the target process.
1113 tcred = __task_cred(task);
1114 if (cred->euid != tcred->suid && cred->euid != tcred->uid &&
1115 cred->uid != tcred->suid && cred->uid != tcred->uid &&
1116 !capable(CAP_SYS_NICE)) {
1123 err = security_task_movememory(task);
1128 err = do_pages_move(mm, task, nr_pages, pages, nodes, status,
1131 err = do_pages_stat(mm, nr_pages, pages, status);
1140 * Call migration functions in the vma_ops that may prepare
1141 * memory in a vm for migration. migration functions may perform
1142 * the migration for vmas that do not have an underlying page struct.
1144 int migrate_vmas(struct mm_struct *mm, const nodemask_t *to,
1145 const nodemask_t *from, unsigned long flags)
1147 struct vm_area_struct *vma;
1150 for (vma = mm->mmap; vma && !err; vma = vma->vm_next) {
1151 if (vma->vm_ops && vma->vm_ops->migrate) {
1152 err = vma->vm_ops->migrate(vma, to, from, flags);