On Tue 29-03-11 22:02:23, Zhu Yanhai wrote:

Hi,

2011/3/29 Michal Hocko [off-list ref]:

quoted

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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