Re: Re: Re: [PATCH 4/13] memcg: force_empty moving account

kamezawa.hiroyu
2008-09-22T15:06:10Z

----- Original Message -----
>On Mon, 2008-09-22 at 23:50 +0900, kamezawa.hiroyu@jp.fujitsu.com wrote:
>> ----- Original Message -----
>> >> + spin_lock_irqsave(&mz->lru_lock, flags);
>> >> + } else {
>> >> + unlock_page(page);
>> >> + put_page(page);
>> >> + }
>> >> + if (atomic_read(&mem->css.cgroup->count) > 0)
>> >> + break;
>> >> }
>> >> spin_unlock_irqrestore(&mz->lru_lock, flags);
>> >
>> >do _NOT_ use yield() ever! unless you know what you're doing, and
>> >probably not even then.
>> >
>> >NAK!
>> Hmm, sorry. cond_resched() is ok ?
>
>depends on what you want to do, please explain what you're trying to do.
>
Sorry again.

This force_empty is called only in following situation
- there is no user threas in this cgroup.
- a user tries to rmdir() this cgroup or explicitly type
echo 1 > ../memory.force_empty.

force_empty() scans lru list of this cgroup and check page_cgroup on the
list one by one. Because there are no tasks in this group, force_empty can
see following racy condtions while scanning.

- global lru tries to remove the page which pointed by page_cgroup
and it is not-on-LRU.
- the page is locked by someone.
....find some lock contetion with invalidation/truncate.
- in later patch, page_cgroup can be on pagevec(i added) and we have to drain
it to remove from LRU.

In above situation, force_empty() have to wait for some event proceeds.

Hmm...detecting busy situation in loop and sleep in out-side-of-loop
is better ? Anyway, ok, I'll rewrite this.

BTW, sched.c::yield() is for what purpose now ?

Thanks,
-Kame