[PATCH 8/12] mm: page migration remove_migration_ptes at lock+unlock level

Hugh Dickins
2015-10-19T05:01:39Z

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>
---
mm/migrate.c | 34 +++++++++++++++++++---------------
1 file changed, 19 insertions(+), 15 deletions(-)

--- migrat.orig/mm/migrate.c 2015-10-18 17:53:22.487335021 -0700
+++ migrat/mm/migrate.c 2015-10-18 17:53:24.858337721 -0700
@@ -722,7 +722,7 @@ static int fallback_migrate_page(struct
* 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
* 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
}

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_
}

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);