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>

1 files changed, 19 insertions, 15 deletions

diff --git a/mm/migrate.c b/mm/migrate.c
index 6d7774ef0e6c..7b44ebdf2d26 100644
--- 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);