mm: memcontrol: shorten the page statistics update slowpath
While moving charges from one memcg to another, page stat updates must
acquire the old memcg's move_lock to prevent double accounting. That
situation is denoted by an increased memcg->move_accounting. However, the
charge moving code declares this way too early for now, even before
summing up the RSS and pre-allocating destination charges.
Shorten this slowpath mode by increasing memcg->move_accounting only right
before walking the task's address space with the intention of actually
moving the pages.
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Reviewed-by: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9d30129..9073d07 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5333,8 +5333,6 @@
static void mem_cgroup_clear_mc(void)
{
- struct mem_cgroup *from = mc.from;
-
/*
* we must clear moving_task before waking up waiters at the end of
* task migration.
@@ -5345,8 +5343,6 @@
mc.from = NULL;
mc.to = NULL;
spin_unlock(&mc.lock);
-
- atomic_dec(&from->moving_account);
}
static int mem_cgroup_can_attach(struct cgroup_subsys_state *css,
@@ -5380,15 +5376,6 @@
VM_BUG_ON(mc.moved_charge);
VM_BUG_ON(mc.moved_swap);
- /*
- * Signal mem_cgroup_begin_page_stat() to take
- * the memcg's move_lock while we're moving
- * its pages to another memcg. Then wait for
- * already started RCU-only updates to finish.
- */
- atomic_inc(&from->moving_account);
- synchronize_rcu();
-
spin_lock(&mc.lock);
mc.from = from;
mc.to = memcg;
@@ -5520,6 +5507,13 @@
struct vm_area_struct *vma;
lru_add_drain_all();
+ /*
+ * Signal mem_cgroup_begin_page_stat() to take the memcg's
+ * move_lock while we're moving its pages to another memcg.
+ * Then wait for already started RCU-only updates to finish.
+ */
+ atomic_inc(&mc.from->moving_account);
+ synchronize_rcu();
retry:
if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
/*
@@ -5552,6 +5546,7 @@
break;
}
up_read(&mm->mmap_sem);
+ atomic_dec(&mc.from->moving_account);
}
static void mem_cgroup_move_task(struct cgroup_subsys_state *css,