[PATCH] More page migration: use migration entries for file pages

This implements the use of migration entries to preserve ptes of file backed
pages during migration.  Processes can therefore be migrated back and forth
without loosing their connection to pagecache pages.

Note that we implement the migration entries only for linear mappings.
Nonlinear mappings still require the unmapping of the ptes for migration.

And another writepage() ugliness shows up.  writepage() can drop the page
lock.  Therefore we have to remove migration ptes before calling writepages()
in order to avoid having migration entries point to unlocked pages.

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

1 files changed, 11 insertions, 0 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index 05d6d73a692d..882a85826bb2 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -596,6 +596,7 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
                                 spin_unlock(&mmlist_lock);
                         }
                         dec_mm_counter(mm, anon_rss);
+#ifdef CONFIG_MIGRATION
                 } else {
                         /*
                          * Store the pfn of the page in a special migration
@@ -604,12 +605,22 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
                          */
                         BUG_ON(!migration);
                         entry = make_migration_entry(page, pte_write(pteval));
+#endif
                 }
                 set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
                 BUG_ON(pte_file(*pte));
         } else
+#ifdef CONFIG_MIGRATION
+        if (migration) {
+                /* Establish migration entry for a file page */
+                swp_entry_t entry;
+                entry = make_migration_entry(page, pte_write(pteval));
+                set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
+        } else
+#endif
                 dec_mm_counter(mm, file_rss);
 
+
         page_remove_rmap(page);
         page_cache_release(page);