The patch titled
memory unplug: migration by kernel
has been added to the -mm tree. Its filename is
memory-unplug-v7-migration-by-kernel.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: memory unplug: migration by kernel
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
In usual, migrate_pages(page,,) is called with holding mm->sem by system call.
(mm here is a mm_struct which maps the migration target page.)
This semaphore helps avoiding some race conditions.
But, if we want to migrate a page by some kernel codes, we have to avoid
some races. This patch adds check code for following race condition.
1. A page which page->mapping==NULL can be target of migration. Then, we have
to check page->mapping before calling try_to_unmap().
2. anon_vma can be freed while page is unmapped, but page->mapping remains as
it was. We drop page->mapcount to be 0. Then we cannot trust page->mapping.
So, use rcu_read_lock() to prevent anon_vma pointed by page->mapping from
being freed during migration.
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Acked-by: Christoph Lameter <clameter@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/migrate.c | 21 +++++++++++++++++++--
1 files changed, 19 insertions(+), 2 deletions(-)
diff -puN mm/migrate.c~memory-unplug-v7-migration-by-kernel mm/migrate.c
--- a/mm/migrate.c~memory-unplug-v7-migration-by-kernel
+++ a/mm/migrate.c
@@ -632,18 +632,35 @@ static int unmap_and_move(new_page_t get
goto unlock;
wait_on_page_writeback(page);
}
-
/*
- * Establish migration ptes or remove ptes
+ * By try_to_unmap(), page->mapcount goes down to 0 here. In this case,
+ * we cannot notice that anon_vma is freed while we migrates a page.
+ * This rcu_read_lock() delays freeing anon_vma pointer until the end
+ * of migration. File cache pages are no problem because of page_lock()
+ */
+ rcu_read_lock();
+ /*
+ * This is a corner case handling.
+ * When a new swap-cache is read into, it is linked to LRU
+ * and treated as swapcache but has no rmap yet.
+ * Calling try_to_unmap() against a page->mapping==NULL page is
+ * BUG. So handle it here.
*/
+ if (!page->mapping)
+ goto rcu_unlock;
+ /* Establish migration ptes or remove ptes */
try_to_unmap(page, 1);
+
if (!page_mapped(page))
rc = move_to_new_page(newpage, page);
if (rc)
remove_migration_ptes(page, page);
+rcu_unlock:
+ rcu_read_unlock();
unlock:
+
unlock_page(page);
if (rc != -EAGAIN) {
_
Patches currently in -mm which might be from kamezawa.hiroyu@xxxxxxxxxxxxxx are
change-zonelist-order-zonelist-order-selection-logic.patch
change-zonelist-order-zonelist-order-selection-logic-add-check_highest_zone-to-build_zonelists_in_zone_order.patch
change-zonelist-order-v6-zonelist-fix.patch
change-zonelist-order-v6-zonelist-fix-2.patch
change-zonelist-order-auto-configuration.patch
change-zonelist-order-documentaion.patch
memory-unplug-v7-migration-by-kernel.patch
memory-unplug-v7-isolate_lru_page-fix.patch
memory-unplug-v7-memory-hotplug-cleanup.patch
memory-unplug-v7-page-isolation.patch
memory-unplug-v7-page-offline.patch
memory-unplug-v7-ia64-interface.patch
-
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