Re: [patch 7/8] vmscan: memcg-aware unevictable page rescue scanner

[Ying Han]

On Thu, Jun 2, 2011 at 3:19 PM, Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
> On Fri, Jun 03, 2011 at 07:01:34AM +0900, Hiroyuki Kamezawa wrote:
>> 2011/6/3 Ying Han <yinghan@xxxxxxxxxx>:
>> > On Thu, Jun 2, 2011 at 6:27 AM, Hiroyuki Kamezawa
>> > <kamezawa.hiroyuki@xxxxxxxxx> wrote:
>> >> 2011/6/1 Johannes Weiner <hannes@xxxxxxxxxxx>:
>> >>> Once the per-memcg lru lists are exclusive, the unevictable page
>> >>> rescue scanner can no longer work on the global zone lru lists.
>> >>>
>> >>> This converts it to go through all memcgs and scan their respective
>> >>> unevictable lists instead.
>> >>>
>> >>> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
>> >>
>> >> Hm, isn't it better to have only one GLOBAL LRU for unevictable pages ?
>> >> memcg only needs counter for unevictable pages and LRU is not necessary
>> >> to be per memcg because we don't reclaim it...
>> >
>> > Hmm. Are we suggesting to keep one un-evictable LRU list for all
>> > memcgs? So we will have
>> > exclusive lru only for file and anon. If so, we are not done to make
>> > all the lru list being exclusive
>> > which is critical later to improve the zone->lru_lock contention
>> > across the memcgs
>> >
>> considering lrulock, yes, maybe you're right.
>
> That's one of the complications.

That should be achievable if we make all the per-memcg lru being
exclusive. So we can switch the global zone->lru_lock
to per-memcg-per-zone lru_lock. We have a prototype of the patch doing
something like that, but we will wait for this effort
being discussed and reviewed.

--Ying

>
>> > Sorry If i misinterpret the suggestion here
>> >
>>
>> My concern is I don't know for what purpose this function is used ..
>
> I am not sure how it's supposed to be used, either.  But it's
> documented to be a 'really big hammer' and it's kicked off from
> userspace.  So I suppose having the thing go through all memcgs bears
> a low risk of being a problem.  My suggestion is we go that way until
> someone complains.
>
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