mm: page migration remove_migration_ptes at lock+unlock level

Clean up page migration a little more by calling remove_migration_ptes()
from the same level, on success or on failure, from __unmap_and_move() or
from unmap_and_move_huge_page().

Don't reset page->mapping of a PageAnon old page in move_to_new_page(),
leave that to when the page is freed.  Except for here in page migration,
it has been an invariant that a PageAnon (bit set in page->mapping) page
stays PageAnon until it is freed, and I think we're safer to keep to that.

And with the above rearrangement, it's necessary because zap_pte_range()
wants to identify whether a migration entry represents a file or an anon
page, to update the appropriate rss stats without waiting on it.

Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/migrate.c b/mm/migrate.c
index 6d7774ef0e6c107b2262a265d8e453e297151568..7b44ebdf2d2684a1dac8ab413592d39c5e775e92 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -722,7 +722,7 @@ static int fallback_migrate_page(struct address_space *mapping,
  *  MIGRATEPAGE_SUCCESS - success
  */
 static int move_to_new_page(struct page *newpage, struct page *page,
-                               int page_was_mapped, enum migrate_mode mode)
+                               enum migrate_mode mode)
 {
        struct address_space *mapping;
        int rc;
@@ -755,19 +755,21 @@ static int move_to_new_page(struct page *newpage, struct page *page,
                 * space which also has its own migratepage callback. This
                 * is the most common path for page migration.
                 */
-               rc = mapping->a_ops->migratepage(mapping,
-                                               newpage, page, mode);
+               rc = mapping->a_ops->migratepage(mapping, newpage, page, mode);
        else
                rc = fallback_migrate_page(mapping, newpage, page, mode);
 
-       if (rc != MIGRATEPAGE_SUCCESS) {
+       /*
+        * When successful, old pagecache page->mapping must be cleared before
+        * page is freed; but stats require that PageAnon be left as PageAnon.
+        */
+       if (rc == MIGRATEPAGE_SUCCESS) {
+               set_page_memcg(page, NULL);
+               if (!PageAnon(page))
+                       page->mapping = NULL;
+       } else {
                set_page_memcg(newpage, NULL);
                newpage->mapping = NULL;
-       } else {
-               set_page_memcg(page, NULL);
-               if (page_was_mapped)
-                       remove_migration_ptes(page, newpage);
-               page->mapping = NULL;
        }
        return rc;
 }
@@ -902,10 +904,11 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
        }
 
        if (!page_mapped(page))
-               rc = move_to_new_page(newpage, page, page_was_mapped, mode);
+               rc = move_to_new_page(newpage, page, mode);
 
-       if (rc && page_was_mapped)
-               remove_migration_ptes(page, page);
+       if (page_was_mapped)
+               remove_migration_ptes(page,
+                       rc == MIGRATEPAGE_SUCCESS ? newpage : page);
 
 out_unlock_both:
        unlock_page(newpage);
@@ -1066,10 +1069,11 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
        }
 
        if (!page_mapped(hpage))
-               rc = move_to_new_page(new_hpage, hpage, page_was_mapped, mode);
+               rc = move_to_new_page(new_hpage, hpage, mode);
 
-       if (rc != MIGRATEPAGE_SUCCESS && page_was_mapped)
-               remove_migration_ptes(hpage, hpage);
+       if (page_was_mapped)
+               remove_migration_ptes(hpage,
+                       rc == MIGRATEPAGE_SUCCESS ? new_hpage : hpage);
 
        unlock_page(new_hpage);