From: Christoph Lameter Date: Fri, 23 Jun 2006 09:03:51 +0000 (-0700) Subject: [PATCH] page migration: simplify migrate_pages() X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=e24f0b8f76cc3dd96f36f5b6a9f020f6c3fce198;p=openwrt%2Fstaging%2Fblogic.git [PATCH] page migration: simplify migrate_pages() Currently migrate_pages() is mess with lots of goto. Extract two functions from migrate_pages() and get rid of the gotos. Plus we can just unconditionally set the locked bit on the new page since we are the only one holding a reference. Locking is to stop others from accessing the page once we establish references to the new page. Remove the list_del from move_to_lru in order to have finer control over list processing. [akpm@osdl.org: add debug check] Signed-off-by: Christoph Lameter Cc: Hugh Dickins Cc: Jes Sorensen Cc: KAMEZAWA Hiroyuki Cc: Lee Schermerhorn Cc: Andi Kleen Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/mm/migrate.c b/mm/migrate.c index b5000d463893..09038163bfec 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -84,7 +84,6 @@ int migrate_prep(void) static inline void move_to_lru(struct page *page) { - list_del(&page->lru); if (PageActive(page)) { /* * lru_cache_add_active checks that @@ -110,6 +109,7 @@ int putback_lru_pages(struct list_head *l) int count = 0; list_for_each_entry_safe(page, page2, l, lru) { + list_del(&page->lru); move_to_lru(page); count++; } @@ -533,12 +533,109 @@ static int fallback_migrate_page(struct address_space *mapping, 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) { + 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 pages isolated + * The second list contains new pages that the isolated pages * can be moved to. * * The function returns after 10 attempts or if no pages @@ -550,7 +647,7 @@ static int fallback_migrate_page(struct address_space *mapping, int migrate_pages(struct list_head *from, struct list_head *to, struct list_head *moved, struct list_head *failed) { - int retry; + int retry = 1; int nr_failed = 0; int pass = 0; struct page *page; @@ -561,118 +658,33 @@ int migrate_pages(struct list_head *from, struct list_head *to, if (!swapwrite) current->flags |= PF_SWAPWRITE; -redo: - retry = 0; - - list_for_each_entry_safe(page, page2, from, lru) { - struct page *newpage = NULL; - struct address_space *mapping; - - cond_resched(); - - rc = 0; - if (page_count(page) == 1) - /* page was freed from under us. So we are done. */ - goto next; - - if (to && list_empty(to)) - break; - - /* - * Skip locked pages during the first two passes to give the - * functions holding the lock time to release the page. Later we - * use lock_page() to have a higher chance of acquiring the - * lock. - */ - rc = -EAGAIN; - if (pass > 2) - lock_page(page); - else - if (TestSetPageLocked(page)) - goto next; - - /* - * Only wait on writeback if we have already done a pass where - * we we may have triggered writeouts for lots of pages. - */ - if (pass > 0) - wait_on_page_writeback(page); - else - if (PageWriteback(page)) - goto unlock_page; - - /* - * Establish migration ptes or remove ptes - */ - rc = -EPERM; - if (try_to_unmap(page, 1) == SWAP_FAIL) - /* A vma has VM_LOCKED set -> permanent failure */ - goto unlock_page; + for(pass = 0; pass < 10 && retry; pass++) { + retry = 0; - rc = -EAGAIN; - if (page_mapped(page)) - goto unlock_page; + list_for_each_entry_safe(page, page2, from, lru) { - newpage = lru_to_page(to); - lock_page(newpage); - /* Prepare mapping for the new page.*/ - newpage->index = page->index; - newpage->mapping = page->mapping; + if (list_empty(to)) + break; - /* - * Pages are properly locked and writeback is complete. - * Try to migrate the page. - */ - mapping = page_mapping(page); - if (!mapping) - rc = migrate_page(mapping, newpage, page); + cond_resched(); - 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); - - unlock_page(newpage); - -unlock_page: - if (rc) - remove_migration_ptes(page, page); + rc = unmap_and_move(lru_to_page(to), page, pass > 2); - unlock_page(page); - -next: - if (rc) { - if (newpage) - newpage->mapping = NULL; - - if (rc == -EAGAIN) + switch(rc) { + case -EAGAIN: retry++; - else { + break; + case 0: + list_move(&page->lru, moved); + break; + default: /* Permanent failure */ list_move(&page->lru, failed); nr_failed++; + break; } - } else { - if (newpage) { - /* Successful migration. Return page to LRU */ - move_to_lru(newpage); - } - list_move(&page->lru, moved); } } - if (retry && pass++ < 10) - goto redo; if (!swapwrite) current->flags &= ~PF_SWAPWRITE;