On Thu, Jan 16, 2020 at 02:01:59PM -0800, David Rientjes wrote:
>On Thu, 16 Jan 2020, Kirill Tkhai wrote:
>
>> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> > index c5b5f74cfd4d..6450bbe394e2 100644
>> > --- a/mm/memcontrol.c
>> > +++ b/mm/memcontrol.c
>> > @@ -5360,10 +5360,12 @@ static int mem_cgroup_move_account(struct page *page,
>> > }
>> >
>> > #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> > - if (compound && !list_empty(page_deferred_list(page))) {
>> > + if (compound) {
>> > spin_lock(&from->deferred_split_queue.split_queue_lock);
>> > - list_del_init(page_deferred_list(page));
>> > - from->deferred_split_queue.split_queue_len--;
>> > + if (!list_empty(page_deferred_list(page))) {
>> > + list_del_init(page_deferred_list(page));
>> > + from->deferred_split_queue.split_queue_len--;
>> > + }
>> > spin_unlock(&from->deferred_split_queue.split_queue_lock);
>> > }
>> > #endif
>> > @@ -5377,11 +5379,13 @@ static int mem_cgroup_move_account(struct page *page,
>> > page->mem_cgroup = to;
>> >
>> > #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> > - if (compound && list_empty(page_deferred_list(page))) {
>> > + if (compound) {
>> > spin_lock(&to->deferred_split_queue.split_queue_lock);
>> > - list_add_tail(page_deferred_list(page),
>> > - &to->deferred_split_queue.split_queue);
>> > - to->deferred_split_queue.split_queue_len++;
>> > + if (list_empty(page_deferred_list(page))) {
>> > + list_add_tail(page_deferred_list(page),
>> > + &to->deferred_split_queue.split_queue);
>> > + to->deferred_split_queue.split_queue_len++;
>> > + }
>> > spin_unlock(&to->deferred_split_queue.split_queue_lock);
>> > }
>> > #endif
>>
>> The patch looks OK for me. But there is another question. I forget, why we unconditionally
>> add a page with empty deferred list to deferred_split_queue. Shouldn't we also check that
>> it was initially in the list? Something like:
>>
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index d4394ae4e5be..0be0136adaa6 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -5289,6 +5289,7 @@ static int mem_cgroup_move_account(struct page *page,
>> struct pglist_data *pgdat;
>> unsigned long flags;
>> unsigned int nr_pages = compound ? hpage_nr_pages(page) : 1;
>> + bool split = false;
>> int ret;
>> bool anon;
>>
>> @@ -5346,6 +5347,7 @@ static int mem_cgroup_move_account(struct page *page,
>> if (!list_empty(page_deferred_list(page))) {
>> list_del_init(page_deferred_list(page));
>> from->deferred_split_queue.split_queue_len--;
>> + split = true;
>> }
>> spin_unlock(&from->deferred_split_queue.split_queue_lock);
>> }
>> @@ -5360,7 +5362,7 @@ static int mem_cgroup_move_account(struct page *page,
>> page->mem_cgroup = to;
>>
>> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> - if (compound) {
>> + if (compound && split) {
>> spin_lock(&to->deferred_split_queue.split_queue_lock);
>> if (list_empty(page_deferred_list(page))) {
>> list_add_tail(page_deferred_list(page),
>>
>
>I think that's a good point, especially considering that the current code
>appears to unconditionally place any compound page on the deferred split
>queue of the destination memcg. The correct list that it should appear
>on, I believe, depends on whether the pmd has been split for the process
>being moved: note the MC_TARGET_PAGE caveat in
>mem_cgroup_move_charge_pte_range() that does not move the charge for
>compound pages with split pmds. So when mem_cgroup_move_account() is
>called with compound == true, we're moving the charge of the entire
>compound page: why would it appear on that memcg's deferred split queue?
Well, Kirill's change is easy to understand, while your statement here is a
bit hard for me. Seems I lack some knowledge about cgroup. I am sorry about
this. :-(
--
Wei Yang
Help you, Help me
