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 <[email protected]> --- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
