On Wed, Dec 12, 2012 at 10:42 AM, Michal Hocko <mhocko@xxxxxxx> wrote:
> On Wed 12-12-12 19:34:46, Michal Hocko wrote:
>> On Wed 12-12-12 10:09:43, Ying Han wrote:
>> [...]
>> > But If i look at the callers of mem_cgroup_iter(), they all look like
>> > the following:
>> >
>> > memcg = mem_cgroup_iter(root, NULL, &reclaim);
>> > do {
>> >
>> > // do something
>> >
>> > memcg = mem_cgroup_iter(root, memcg, &reclaim);
>> > } while (memcg);
>> >
>> > So we get out of the loop when memcg returns as NULL, where the
>> > last_visited is cached as NULL as well thus no css_get(). That is what
>> > I meant by "each reclaim thread closes the loop".
>>
>> OK
>>
>> > If that is true, the current implementation of mem_cgroup_iter_break()
>> > changes that.
>>
>> I do not understand this though. Why should we touch the zone-iter
>> there? Just consider, if we did that then all the parallel targeted
>
> Bahh, parallel is only confusing here. Say first child triggers a hard
> limit reclaim then root of the hierarchy will be reclaimed first.
> iter_break would reset iter->last_visited. Then B triggers the same
> reclaim but we will start again from root rather than the first child
> because it doesn't know where the other one stopped.
>
> Hope this clarifies it and sorry for all the confusion.
Yes it does.
I missed the point of how the target reclaim are currently
implemented, and part of the reason is because I don't understand why
that is the case from the beginning.
Off topic of the following discussion.
Take the following hierarchy as example:
root
/ | \
a b c
| \
d e
| \
g h
Let's say c hits its hardlimit and then triggers target reclaim. There
are two reclaimers at the moment and reclaimer_1 starts earlier. The
cgroup_next_descendant_pre() returns in order : c->d->g->e->h
Then we might get the reclaim result as the following where each
reclaimer keep hitting one node of the sub-tree for all the priorities
like the following:
reclaimer_1 reclaimer_2
priority 12 c d
... c d
... c d
... c d
0 c d
However, this is not how global reclaim works:
the cgroup_next_descendant_pre returns in order: root->a->b->c->d->g->e->h
reclaimer_1 reclaimer_1 reclaimer_1 reclaimer_2
priority 12 root a b c
... root a b c
...
...
0
There is no reason for me to think of why target reclaim behave
differently from global reclaim, which the later one is just the
target reclaim of root cgroup.
--Ying
>
>> reclaimers (! global case) would hammer the first node (root) as they
>> wouldn't continue where the last one finished.
>>
>> [...]
>>
>> Thanks!
> --
> Michal Hocko
> SUSE Labs
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>