/* * Memory Migration functionality - linux/mm/migration.c * * Copyright (C) 2006 Silicon Graphics, Inc., Christoph Lameter * * Page migration was first developed in the context of the memory hotplug * project. The main authors of the migration code are: * * IWAMOTO Toshihiro * Hirokazu Takahashi * Dave Hansen * Christoph Lameter */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include "internal.h" /* The maximum number of pages to take off the LRU for migration */ #define MIGRATE_CHUNK_SIZE 256 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru)) /* * Isolate one page from the LRU lists. If successful put it onto * the indicated list with elevated page count. * * Result: * -EBUSY: page not on LRU list * 0: page removed from LRU list and added to the specified list. */ int isolate_lru_page(struct page *page, struct list_head *pagelist) { int ret = -EBUSY; if (PageLRU(page)) { struct zone *zone = page_zone(page); spin_lock_irq(&zone->lru_lock); if (PageLRU(page)) { ret = 0; get_page(page); ClearPageLRU(page); if (PageActive(page)) del_page_from_active_list(zone, page); else del_page_from_inactive_list(zone, page); list_add_tail(&page->lru, pagelist); } spin_unlock_irq(&zone->lru_lock); } return ret; } /* * migrate_prep() needs to be called after we have compiled the list of pages * to be migrated using isolate_lru_page() but before we begin a series of calls * to migrate_pages(). */ int migrate_prep(void) { /* * Clear the LRU lists so pages can be isolated. * Note that pages may be moved off the LRU after we have * drained them. Those pages will fail to migrate like other * pages that may be busy. */ lru_add_drain_all(); return 0; } static inline void move_to_lru(struct page *page) { if (PageActive(page)) { /* * lru_cache_add_active checks that * the PG_active bit is off. */ ClearPageActive(page); lru_cache_add_active(page); } else { lru_cache_add(page); } put_page(page); } /* * Add isolated pages on the list back to the LRU. * * returns the number of pages put back. */ int putback_lru_pages(struct list_head *l) { struct page *page; struct page *page2; int count = 0; list_for_each_entry_safe(page, page2, l, lru) { list_del(&page->lru); move_to_lru(page); count++; } return count; } static inline int is_swap_pte(pte_t pte) { return !pte_none(pte) && !pte_present(pte) && !pte_file(pte); } /* * Restore a potential migration pte to a working pte entry */ static void remove_migration_pte(struct vm_area_struct *vma, struct page *old, struct page *new) { struct mm_struct *mm = vma->vm_mm; swp_entry_t entry; pgd_t *pgd; pud_t *pud; pmd_t *pmd; pte_t *ptep, pte; spinlock_t *ptl; unsigned long addr = page_address_in_vma(new, vma); if (addr == -EFAULT) return; pgd = pgd_offset(mm, addr); if (!pgd_present(*pgd)) return; pud = pud_offset(pgd, addr); if (!pud_present(*pud)) return; pmd = pmd_offset(pud, addr); if (!pmd_present(*pmd)) return; ptep = pte_offset_map(pmd, addr); if (!is_swap_pte(*ptep)) { pte_unmap(ptep); return; } ptl = pte_lockptr(mm, pmd); spin_lock(ptl); pte = *ptep; if (!is_swap_pte(pte)) goto out; entry = pte_to_swp_entry(pte); if (!is_migration_entry(entry) || migration_entry_to_page(entry) != old) goto out; get_page(new); pte = pte_mkold(mk_pte(new, vma->vm_page_prot)); if (is_write_migration_entry(entry)) pte = pte_mkwrite(pte); set_pte_at(mm, addr, ptep, pte); if (PageAnon(new)) page_add_anon_rmap(new, vma, addr); else page_add_file_rmap(new); /* No need to invalidate - it was non-present before */ update_mmu_cache(vma, addr, pte); lazy_mmu_prot_update(pte); out: pte_unmap_unlock(ptep, ptl); } /* * Note that remove_file_migration_ptes will only work on regular mappings, * Nonlinear mappings do not use migration entries. */ static void remove_file_migration_ptes(struct page *old, struct page *new) { struct vm_area_struct *vma; struct address_space *mapping = page_mapping(new); struct prio_tree_iter iter; pgoff_t pgoff = new->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); if (!mapping) return; spin_lock(&mapping->i_mmap_lock); vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) remove_migration_pte(vma, old, new); spin_unlock(&mapping->i_mmap_lock); } /* * Must hold mmap_sem lock on at least one of the vmas containing * the page so that the anon_vma cannot vanish. */ static void remove_anon_migration_ptes(struct page *old, struct page *new) { struct anon_vma *anon_vma; struct vm_area_struct *vma; unsigned long mapping; mapping = (unsigned long)new->mapping; if (!mapping || (mapping & PAGE_MAPPING_ANON) == 0) return; /* * We hold the mmap_sem lock. So no need to call page_lock_anon_vma. */ anon_vma = (struct anon_vma *) (mapping - PAGE_MAPPING_ANON); spin_lock(&anon_vma->lock); list_for_each_entry(vma, &anon_vma->head, anon_vma_node) remove_migration_pte(vma, old, new); spin_unlock(&anon_vma->lock); } /* * Get rid of all migration entries and replace them by * references to the indicated page. */ static void remove_migration_ptes(struct page *old, struct page *new) { if (PageAnon(new)) remove_anon_migration_ptes(old, new); else remove_file_migration_ptes(old, new); } /* * Something used the pte of a page under migration. We need to * get to the page and wait until migration is finished. * When we return from this function the fault will be retried. * * This function is called from do_swap_page(). */ void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd, unsigned long address) { pte_t *ptep, pte; spinlock_t *ptl; swp_entry_t entry; struct page *page; ptep = pte_offset_map_lock(mm, pmd, address, &ptl); pte = *ptep; if (!is_swap_pte(pte)) goto out; entry = pte_to_swp_entry(pte); if (!is_migration_entry(entry)) goto out; page = migration_entry_to_page(entry); get_page(page); pte_unmap_unlock(ptep, ptl); wait_on_page_locked(page); put_page(page); return; out: pte_unmap_unlock(ptep, ptl); } /* * Replace the page in the mapping. * * The number of remaining references must be: * 1 for anonymous pages without a mapping * 2 for pages with a mapping * 3 for pages with a mapping and PagePrivate set. */ static int migrate_page_move_mapping(struct address_space *mapping, struct page *newpage, struct page *page) { struct page **radix_pointer; if (!mapping) { /* Anonymous page */ if (page_count(page) != 1) return -EAGAIN; return 0; } write_lock_irq(&mapping->tree_lock); radix_pointer = (struct page **)radix_tree_lookup_slot( &mapping->page_tree, page_index(page)); if (page_count(page) != 2 + !!PagePrivate(page) || *radix_pointer != page) { write_unlock_irq(&mapping->tree_lock); return -EAGAIN; } /* * Now we know that no one else is looking at the page. */ get_page(newpage); #ifdef CONFIG_SWAP if (PageSwapCache(page)) { SetPageSwapCache(newpage); set_page_private(newpage, page_private(page)); } #endif *radix_pointer = newpage; __put_page(page); write_unlock_irq(&mapping->tree_lock); return 0; } /* * Copy the page to its new location */ static void migrate_page_copy(struct page *newpage, struct page *page) { copy_highpage(newpage, page); if (PageError(page)) SetPageError(newpage); if (PageReferenced(page)) SetPageReferenced(newpage); if (PageUptodate(page)) SetPageUptodate(newpage); if (PageActive(page)) SetPageActive(newpage); if (PageChecked(page)) SetPageChecked(newpage); if (PageMappedToDisk(page)) SetPageMappedToDisk(newpage); if (PageDirty(page)) { clear_page_dirty_for_io(page); set_page_dirty(newpage); } #ifdef CONFIG_SWAP ClearPageSwapCache(page); #endif ClearPageActive(page); ClearPagePrivate(page); set_page_private(page, 0); page->mapping = NULL; /* * If any waiters have accumulated on the new page then * wake them up. */ if (PageWriteback(newpage)) end_page_writeback(newpage); } /************************************************************ * Migration functions ***********************************************************/ /* Always fail migration. Used for mappings that are not movable */ int fail_migrate_page(struct address_space *mapping, struct page *newpage, struct page *page) { return -EIO; } EXPORT_SYMBOL(fail_migrate_page); /* * Common logic to directly migrate a single page suitable for * pages that do not use PagePrivate. * * Pages are locked upon entry and exit. */ int migrate_page(struct address_space *mapping, struct page *newpage, struct page *page) { int rc; BUG_ON(PageWriteback(page)); /* Writeback must be complete */ rc = migrate_page_move_mapping(mapping, newpage, page); if (rc) return rc; migrate_page_copy(newpage, page); return 0; } EXPORT_SYMBOL(migrate_page); /* * Migration function for pages with buffers. This function can only be used * if the underlying filesystem guarantees that no other references to "page" * exist. */ int buffer_migrate_page(struct address_space *mapping, struct page *newpage, struct page *page) { struct buffer_head *bh, *head; int rc; if (!page_has_buffers(page)) return migrate_page(mapping, newpage, page); head = page_buffers(page); rc = migrate_page_move_mapping(mapping, newpage, page); if (rc) return rc; bh = head; do { get_bh(bh); lock_buffer(bh); bh = bh->b_this_page; } while (bh != head); ClearPagePrivate(page); set_page_private(newpage, page_private(page)); set_page_private(page, 0); put_page(page); get_page(newpage); bh = head; do { set_bh_page(bh, newpage, bh_offset(bh)); bh = bh->b_this_page; } while (bh != head); SetPagePrivate(newpage); migrate_page_copy(newpage, page); bh = head; do { unlock_buffer(bh); put_bh(bh); bh = bh->b_this_page; } while (bh != head); return 0; } EXPORT_SYMBOL(buffer_migrate_page); /* * Writeback a page to clean the dirty state */ static int writeout(struct address_space *mapping, struct page *page) { struct writeback_control wbc = { .sync_mode = WB_SYNC_NONE, .nr_to_write = 1, .range_start = 0, .range_end = LLONG_MAX, .nonblocking = 1, .for_reclaim = 1 }; int rc; if (!mapping->a_ops->writepage) /* No write method for the address space */ return -EINVAL; if (!clear_page_dirty_for_io(page)) /* Someone else already triggered a write */ return -EAGAIN; /* * A dirty page may imply that the underlying filesystem has * the page on some queue. So the page must be clean for * migration. Writeout may mean we loose the lock and the * page state is no longer what we checked for earlier. * At this point we know that the migration attempt cannot * be successful. */ remove_migration_ptes(page, page); rc = mapping->a_ops->writepage(page, &wbc); if (rc < 0) /* I/O Error writing */ return -EIO; if (rc != AOP_WRITEPAGE_ACTIVATE) /* unlocked. Relock */ lock_page(page); return -EAGAIN; } /* * Default handling if a filesystem does not provide a migration function. */ static int fallback_migrate_page(struct address_space *mapping, struct page *newpage, struct page *page) { if (PageDirty(page)) return writeout(mapping, page); /* * Buffers may be managed in a filesystem specific way. * We must have no buffers or drop them. */ if (page_has_buffers(page) && !try_to_release_page(page, GFP_KERNEL)) return -EAGAIN; return migrate_page(mapping, newpage, page); } /* * Move a page to a newly allocated page * The page is locked and all ptes have been successfully removed. * * The new page will have replaced the old page if this function * is successful. */ static int move_to_new_page(struct page *newpage, struct page *page) { struct address_space *mapping; int rc; /* * Block others from accessing the page when we get around to * establishing additional references. We are the only one * holding a reference to the new page at this point. */ if (TestSetPageLocked(newpage)) BUG(); /* Prepare mapping for the new page.*/ newpage->index = page->index; newpage->mapping = page->mapping; mapping = page_mapping(page); if (!mapping) rc = migrate_page(mapping, newpage, page); else if (mapping->a_ops->migratepage) /* * Most pages have a mapping and most filesystems * should provide a migration function. Anonymous * pages are part of swap space which also has its * own migration function. This is the most common * path for page migration. */ rc = mapping->a_ops->migratepage(mapping, newpage, page); else rc = fallback_migrate_page(mapping, newpage, page); if (!rc) remove_migration_ptes(page, newpage); else newpage->mapping = NULL; unlock_page(newpage); return rc; } /* * Obtain the lock on page, remove all ptes and migrate the page * to the newly allocated page in newpage. */ static int unmap_and_move(struct page *newpage, struct page *page, int force) { int rc = 0; if (page_count(page) == 1) /* page was freed from under us. So we are done. */ goto ret; rc = -EAGAIN; if (TestSetPageLocked(page)) { if (!force) goto ret; lock_page(page); } if (PageWriteback(page)) { if (!force) goto unlock; wait_on_page_writeback(page); } /* * Establish migration ptes or remove ptes */ if (try_to_unmap(page, 1) != SWAP_FAIL) { if (!page_mapped(page)) rc = move_to_new_page(newpage, page); } else /* A vma has VM_LOCKED set -> permanent failure */ rc = -EPERM; if (rc) remove_migration_ptes(page, page); unlock: unlock_page(page); ret: if (rc != -EAGAIN) { /* * A page that has been migrated has all references * removed and will be freed. A page that has not been * migrated will have kepts its references and be * restored. */ list_del(&page->lru); move_to_lru(page); list_del(&newpage->lru); move_to_lru(newpage); } return rc; } /* * migrate_pages * * Two lists are passed to this function. The first list * contains the pages isolated from the LRU to be migrated. * The second list contains new pages that the isolated pages * can be moved to. * * The function returns after 10 attempts or if no pages * are movable anymore because to has become empty * or no retryable pages exist anymore. All pages will be * retruned to the LRU or freed. * * Return: Number of pages not migrated. */ int migrate_pages(struct list_head *from, struct list_head *to) { int retry = 1; int nr_failed = 0; int pass = 0; struct page *page; struct page *page2; int swapwrite = current->flags & PF_SWAPWRITE; int rc; if (!swapwrite) current->flags |= PF_SWAPWRITE; for(pass = 0; pass < 10 && retry; pass++) { retry = 0; list_for_each_entry_safe(page, page2, from, lru) { if (list_empty(to)) break; cond_resched(); rc = unmap_and_move(lru_to_page(to), page, pass > 2); switch(rc) { case -EAGAIN: retry++; break; case 0: break; default: /* Permanent failure */ nr_failed++; break; } } } if (!swapwrite) current->flags &= ~PF_SWAPWRITE; putback_lru_pages(from); return nr_failed + retry; } /* * Migrate the list 'pagelist' of pages to a certain destination. * * Specify destination with either non-NULL vma or dest_node >= 0 * Return the number of pages not migrated or error code */ int migrate_pages_to(struct list_head *pagelist, struct vm_area_struct *vma, int dest) { LIST_HEAD(newlist); int err = 0; unsigned long offset = 0; int nr_pages; int nr_failed = 0; struct page *page; struct list_head *p; redo: nr_pages = 0; list_for_each(p, pagelist) { if (vma) { /* * The address passed to alloc_page_vma is used to * generate the proper interleave behavior. We fake * the address here by an increasing offset in order * to get the proper distribution of pages. * * No decision has been made as to which page * a certain old page is moved to so we cannot * specify the correct address. */ page = alloc_page_vma(GFP_HIGHUSER, vma, offset + vma->vm_start); offset += PAGE_SIZE; } else page = alloc_pages_node(dest, GFP_HIGHUSER, 0); if (!page) { err = -ENOMEM; goto out; } list_add_tail(&page->lru, &newlist); nr_pages++; if (nr_pages > MIGRATE_CHUNK_SIZE) break; } err = migrate_pages(pagelist, &newlist); if (err >= 0) { nr_failed += err; if (list_empty(&newlist) && !list_empty(pagelist)) goto redo; } out: /* Calculate number of leftover pages */ list_for_each(p, pagelist) nr_failed++; return nr_failed; }