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@xxxxxxxxxxx>
---
mm/memcontrol.c | 21 ++++++++-------------
1 file changed, 8 insertions(+), 13 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c50176429fa3..23cf27cca370 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5263,8 +5263,6 @@ static void __mem_cgroup_clear_mc(void)
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.
@@ -5275,8 +5273,6 @@ static void mem_cgroup_clear_mc(void)
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,
@@ -5310,15 +5306,6 @@ static int mem_cgroup_can_attach(struct cgroup_subsys_state *css,
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;
@@ -5450,6 +5437,13 @@ static void mem_cgroup_move_charge(struct mm_struct *mm)
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))) {
/*
@@ -5482,6 +5476,7 @@ retry:
break;
}
up_read(&mm->mmap_sem);
+ atomic_dec(&mc.from->moving_account);
}
static void mem_cgroup_move_task(struct cgroup_subsys_state *css,
--
2.1.2
--
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