memcg: simple migration handling
Now, management of "charge" under page migration is done under following
manner. (Assume migrate page contents from oldpage to newpage)
before
- "newpage" is charged before migration.
at success.
- "oldpage" is uncharged at somewhere(unmap, radix-tree-replace)
at failure
- "newpage" is uncharged.
- "oldpage" is charged if necessary (*1)
But (*1) is not reliable....because of GFP_ATOMIC.
This patch tries to change behavior as following by charge/commit/cancel ops.
before
- charge PAGE_SIZE (no target page)
success
- commit charge against "newpage".
failure
- commit charge against "oldpage".
(PCG_USED bit works effectively to avoid double-counting)
- if "oldpage" is obsolete, cancel charge of PAGE_SIZE.
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/migrate.c b/mm/migrate.c
index 246dcb9..a30ea5f 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -121,20 +121,6 @@
if (!is_migration_entry(entry) || migration_entry_to_page(entry) != old)
goto out;
- /*
- * Yes, ignore the return value from a GFP_ATOMIC mem_cgroup_charge.
- * Failure is not an option here: we're now expected to remove every
- * migration pte, and will cause crashes otherwise. Normally this
- * is not an issue: mem_cgroup_prepare_migration bumped up the old
- * page_cgroup count for safety, that's now attached to the new page,
- * so this charge should just be another incrementation of the count,
- * to keep in balance with rmap.c's mem_cgroup_uncharging. But if
- * there's been a force_empty, those reference counts may no longer
- * be reliable, and this charge can actually fail: oh well, we don't
- * make the situation any worse by proceeding as if it had succeeded.
- */
- mem_cgroup_charge_migrate_fixup(new, mm, GFP_ATOMIC);
-
get_page(new);
pte = pte_mkold(mk_pte(new, vma->vm_page_prot));
if (is_write_migration_entry(entry))
@@ -378,9 +364,6 @@
anon = PageAnon(page);
page->mapping = NULL;
- if (!anon) /* This page was removed from radix-tree. */
- mem_cgroup_uncharge_cache_page(page);
-
/*
* If any waiters have accumulated on the new page then
* wake them up.
@@ -614,6 +597,7 @@
struct page *newpage = get_new_page(page, private, &result);
int rcu_locked = 0;
int charge = 0;
+ struct mem_cgroup *mem;
if (!newpage)
return -ENOMEM;
@@ -623,24 +607,26 @@
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 (!trylock_page(page)) {
if (!force)
goto move_newpage;
lock_page(page);
}
+ /* charge against new page */
+ charge = mem_cgroup_prepare_migration(page, &mem);
+ if (charge == -ENOMEM) {
+ rc = -ENOMEM;
+ goto unlock;
+ }
+ BUG_ON(charge);
+
if (PageWriteback(page)) {
if (!force)
- goto unlock;
+ goto uncharge;
wait_on_page_writeback(page);
}
/*
@@ -693,7 +679,9 @@
rcu_unlock:
if (rcu_locked)
rcu_read_unlock();
-
+uncharge:
+ if (!charge)
+ mem_cgroup_end_migration(mem, page, newpage);
unlock:
unlock_page(page);
@@ -709,8 +697,6 @@
}
move_newpage:
- if (!charge)
- mem_cgroup_end_migration(newpage);
/*
* Move the new page to the LRU. If migration was not successful
