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 <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
e8589cc189