[PATCH] page migration: fail if page is in a vma flagged VM_LOCKED

page migration currently simply retries a couple of times if try_to_unmap()
fails without inspecting the return code.

However, SWAP_FAIL indicates that the page is in a vma that has the
VM_LOCKED flag set (if ignore_refs ==1).  We can check for that return code
and avoid retrying the migration.

migrate_page_remove_references() now needs to return a reason why the
failure occured.  So switch migrate_page_remove_references to use -Exx
style error messages.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 16 insertions, 8 deletions

diff --git a/fs/buffer.c b/fs/buffer.c
index 62cfd17dc5fe..a9b399402007 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -3060,6 +3060,7 @@ int buffer_migrate_page(struct page *newpage, struct page *page)
 {
         struct address_space *mapping = page->mapping;
         struct buffer_head *bh, *head;
+        int rc;
 
         if (!mapping)
                 return -EAGAIN;
@@ -3069,8 +3070,9 @@ int buffer_migrate_page(struct page *newpage, struct page *page)
 
         head = page_buffers(page);
 
-        if (migrate_page_remove_references(newpage, page, 3))
-                return -EAGAIN;
+        rc = migrate_page_remove_references(newpage, page, 3);
+        if (rc)
+                return rc;
 
         bh = head;
         do {
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7ccf763bb30b..4fe7e3aa02e2 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -700,7 +700,7 @@ int migrate_page_remove_references(struct page *newpage,
          * the page.
          */
         if (!mapping || page_mapcount(page) + nr_refs != page_count(page))
-                return 1;
+                return -EAGAIN;
 
         /*
          * Establish swap ptes for anonymous pages or destroy pte
@@ -721,13 +721,15 @@ int migrate_page_remove_references(struct page *newpage,
          * If the page was not migrated then the PageSwapCache bit
          * is still set and the operation may continue.
          */
-        try_to_unmap(page, 1);
+        if (try_to_unmap(page, 1) == SWAP_FAIL)
+                /* A vma has VM_LOCKED set -> Permanent failure */
+                return -EPERM;
 
         /*
          * Give up if we were unable to remove all mappings.
          */
         if (page_mapcount(page))
-                return 1;
+                return -EAGAIN;
 
         write_lock_irq(&mapping->tree_lock);
 
@@ -738,7 +740,7 @@ int migrate_page_remove_references(struct page *newpage,
         if (!page_mapping(page) || page_count(page) != nr_refs ||
                         *radix_pointer != page) {
                 write_unlock_irq(&mapping->tree_lock);
-                return 1;
+                return -EAGAIN;
         }
 
         /*
@@ -813,10 +815,14 @@ EXPORT_SYMBOL(migrate_page_copy);
  */
 int migrate_page(struct page *newpage, struct page *page)
 {
+        int rc;
+
         BUG_ON(PageWriteback(page));    /* Writeback must be complete */
 
-        if (migrate_page_remove_references(newpage, page, 2))
-                return -EAGAIN;
+        rc = migrate_page_remove_references(newpage, page, 2);
+
+        if (rc)
+                return rc;
 
         migrate_page_copy(newpage, page);