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

[Michal Hocko <mhocko@suse.cz>]

On Tue 29-03-11 22:02:23, Zhu Yanhai wrote:
> Hi,
> 
> 2011/3/29 Michal Hocko <mhocko@suse.cz>:
> > 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.

But we would still have to isolate and put back a lot of pages
potentially. If we do not have those pages on the list we will skip them
automatically.

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

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