Re: [RFC 0/3] Implementation of cgroup isolation

[Zhu Yanhai]

Hi,

2011/3/29 Michal Hocko <mhocko@xxxxxxx>:
> Isn't this an overhead that would slow the whole thing down. Consider
> that you would need to lookup page_cgroup for every page and touch
> mem_cgroup to get the limit.

Current almost has did such things, say the direct reclaim path:
shrink_inactive_list()
   ->isolate_pages_global()
      ->isolate_lru_pages()
         ->mem_cgroup_del_lru(for each page it wants to isolate)
            and in mem_cgroup_del_lru() we have:
[code]
	pc = lookup_page_cgroup(page);
	/*
	 * Used bit is set without atomic ops but after smp_wmb().
	 * For making pc->mem_cgroup visible, insert smp_rmb() here.
	 */
	smp_rmb();
	/* unused or root page is not rotated. */
	if (!PageCgroupUsed(pc) || mem_cgroup_is_root(pc->mem_cgroup))
		return;
[/code]
By calling mem_cgroup_is_root(pc->mem_cgroup) we already brought the
struct mem_cgroup into cache.
So probably things won't get worse at least.

Thanks,
Zhu Yanhai

> The point of the isolation is to not touch the global reclaim path at
> all.
>
>> 3) shrink the cgroups who have set a reserve_limit, and leave them with only
>> the reserve_limit bytes they need. if nr_reclaimed is meet, goto finish.
>> 4) OOM
>>
>> Does it make sense?
>
> It sounds like a good thing - in that regard it is more generic than
> a simple flag - but I am afraid that the implementation wouldn't be
> that easy to preserve the performance and keep the balance between
> groups. But maybe it can be done without too much cost.
>
> Thanks
> --
> Michal Hocko
> SUSE Labs
> SUSE LINUX s.r.o.
> Lihovarska 1060/12
> 190 00 Praha 9
> Czech Republic
>
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