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memcg: better migration handling

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This patch changes page migration under memory controller to use a
different algorithm.  (thanks to Christoph for new idea.)

Before:
 - page_cgroup is migrated from an old page to a new page.
After:
 - a new page is accounted , no reuse of page_cgroup.

Pros:

 - We can avoid compliated lock depndencies and races in migration.

Cons:

 - new param to mem_cgroup_charge_common().

 - mem_cgroup_getref() is added for handling ref_cnt ping-pong.

This version simplifies complicated lock dependency in page migraiton
under memory resource controller.

  new refcnt sequence is following.

a mapped page:
  prepage_migration() ..... +1 to NEW page
  try_to_unmap()      ..... all refs to OLD page is gone.
  move_pages()        ..... +1 to NEW page if page cache.
  remap...            ..... all refs from *map* is added to NEW one.
  end_migration()     ..... -1 to New page.

  page's mapcount + (page_is_cache) refs are added to NEW one.

Signed-off-by: KAMEZAWA Hiroyuki <[email protected]>
Cc: Balbir Singh <[email protected]>
Cc: Pavel Emelyanov <[email protected]>
Cc: Li Zefan <[email protected]>
Cc: YAMAMOTO Takashi <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Christoph Lameter <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
KAMEZAWA Hiroyuki 2008-07-25 01:47:10 -07:00 • committed by Linus Torvalds
commit e8589cc189
3 changed files with 86 additions and 75 deletions
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22
mm/migrate.c
View file

@ -358,6 +358,10 @@ static int migrate_page_move_mapping(struct address_space *mapping,
__inc_zone_page_state(newpage, NR_FILE_PAGES);
write_unlock_irq(&mapping->tree_lock);
if (!PageSwapCache(newpage)) {
mem_cgroup_uncharge_page(page);
mem_cgroup_getref(newpage);
}
return 0;
}
@ -611,7 +615,6 @@ static int move_to_new_page(struct page *newpage, struct page *page)
rc = fallback_migrate_page(mapping, newpage, page);
if (!rc) {
mem_cgroup_page_migration(page, newpage);
remove_migration_ptes(page, newpage);
} else
newpage->mapping = NULL;
@ -641,6 +644,14 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
/* page was freed from under us. So we are done. */
goto move_newpage;
charge = mem_cgroup_prepare_migration(page, newpage);
if (charge == -ENOMEM) {
rc = -ENOMEM;
goto move_newpage;
}
/* prepare cgroup just returns 0 or -ENOMEM */
BUG_ON(charge);
rc = -EAGAIN;
if (TestSetPageLocked(page)) {
if (!force)
@ -692,19 +703,14 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
goto rcu_unlock;
}
charge = mem_cgroup_prepare_migration(page);
/* Establish migration ptes or remove ptes */
try_to_unmap(page, 1);
if (!page_mapped(page))
rc = move_to_new_page(newpage, page);
if (rc) {
if (rc)
remove_migration_ptes(page, page);
if (charge)
mem_cgroup_end_migration(page);
} else if (charge)
mem_cgroup_end_migration(newpage);
rcu_unlock:
if (rcu_locked)
rcu_read_unlock();
@ -725,6 +731,8 @@ unlock:
}
move_newpage:
if (!charge)
mem_cgroup_end_migration(newpage);
/*
* Move the new page to the LRU. If migration was not successful
* then this will free the page.