Re: [RFI] Shared accounting for memory resource controller

[Balbir Singh <balbir@linux.vnet.ibm.com>]

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-04-08 17:54:09]:

> On Wed, 8 Apr 2009 14:19:52 +0530
> Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> 
> > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-04-08 17:03:41]:
> > 
> > > On Wed, 8 Apr 2009 13:18:09 +0530
> > > Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> > > 
> > > > > > 3. Using the above, we can then try to (using an algorithm you
> > > > > > proposed), try to do some work for figuring out the shared percentage.
> > > > > > 
> > > > > This is the point. At last. Why "# of shared pages" is important ?
> > > > > 
> > > > 
> > > > I posted this in my motivation yesterday. # of shared pages can help
> > > > plan the system better and the size of the cgroup. A cgroup might have
> > > > small usage_in_bytes but large number of shared pages. We need a
> > > > metric that can help figure out the fair usage of the cgroup.
> > > > 
> > > I don't fully understand but NR_FILE_MAPPED is an information in /proc/meminfo.
> > > I personally think I want to support information in /proc/meminfo per memcg.
> > > 
> > > Hmm ? then, if you add a hook, it seems
> > > == mm/rmap.c
> > >  689 void page_add_file_rmap(struct page *page)
> > >  690 {
> > >  691         if (atomic_inc_and_test(&page->_mapcount))
> > >  692                 __inc_zone_page_state(page, NR_FILE_MAPPED);
> > >  693 }
> > > ==  page_remove_rmap(struct page *page)
> > >  739                 __dec_zone_page_state(page,
> > >  740                         PageAnon(page) ? NR_ANON_PAGES : NR_FILE_MAPPED);
> > > ==
> > > 
> > > Is good place to go, maybe.
> > > 
> > > page->page_cgroup->mem_cgroup-> inc/dec counter ?
> > > 
> > > Maybe the patch itself will be simple, overhead is unknown..
> > 
> > I thought of the same thing, but then moved to the following
> > 
> > ... mem_cgroup_charge_statistics(..) {
> >  if (page_mapcount(page) == 0 && page_is_file_cache(page))
> >     __mem_cgroup_stat_add_safe(cpustat, MEM_CGROUP_STAT_FILE_RSS, val);
> > 
> > But I've not yet tested the end result
> > 
> I think 
>  - at uncharge:
>    charge_statistics is only called when FILE CACHE is removed from radix-tree.
>    mem_cgroup_uncharge() is called only when PageAnon(page).

Good point, I missed it, testing would have caught it.

>  - at charge:
>    charge_statistics is only called when FILE CACHE is added to radix-tree.
> 
> This "checking only radix-tree insert/delete" help us to remove most of overheads
> on FILE CACHE.
> 
> So, adding new hooks to page_add_file_rmap() and page_remove_rmap()
> is a way to go. (and easy to understand because we account it at the same time
> NR_FILE_MAPPED is modified.)

Agreed.

-- 
	Balbir

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