linux-kernel - Re: [patch 7/8] vmscan: memcg-aware unevictable page rescue scanner

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Date:	Mon, 13 Jun 2011 13:18:57 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Ying Han <yinghan@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>, Greg Thelen <gthelen@...gle.com>,
	Michel Lespinasse <walken@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 7/8] vmscan: memcg-aware unevictable page rescue scanner

On Mon 13-06-11 12:30:32, Johannes Weiner wrote:
> On Mon, Jun 13, 2011 at 11:42:03AM +0200, Michal Hocko wrote:
> > On Wed 01-06-11 08:25:18, Johannes Weiner wrote:
> > > Once the per-memcg lru lists are exclusive, the unevictable page
> > > rescue scanner can no longer work on the global zone lru lists.
> > > 
> > > This converts it to go through all memcgs and scan their respective
> > > unevictable lists instead.
> > > 
> > > Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> > 
> > Just a minor naming thing.
> > 
> > Other than that looks good to me.
> > Reviewed-by: Michal Hocko <mhocko@...e.cz>
> > 
> > > --- a/include/linux/memcontrol.h
> > > +++ b/include/linux/memcontrol.h
> > [...]
> > > +struct page *mem_cgroup_lru_to_page(struct zone *zone, struct mem_cgroup *mem,
> > > +				    enum lru_list lru)
> > > +{
> > > +	struct mem_cgroup_per_zone *mz;
> > > +	struct page_cgroup *pc;
> > > +
> > > +	mz = mem_cgroup_zoneinfo(mem, zone_to_nid(zone), zone_idx(zone));
> > > +	pc = list_entry(mz->lists[lru].prev, struct page_cgroup, lru);
> > > +	return lookup_cgroup_page(pc);
> > > +}
> > > +
> > [...]
> > > --- a/mm/vmscan.c
> > > +++ b/mm/vmscan.c
> > > @@ -3233,6 +3233,14 @@ void scan_mapping_unevictable_pages(struct address_space *mapping)
> > >  
> > >  }
> > >  
> > > +static struct page *lru_tailpage(struct zone *zone, struct mem_cgroup *mem,
> > > +				 enum lru_list lru)
> > > +{
> > > +	if (mem)
> > > +		return mem_cgroup_lru_to_page(zone, mem, lru);
> > > +	return lru_to_page(&zone->lru[lru].list);
> > > +}
> > 
> > Wouldn't it better to have those names consistent?
> > mem_cgroup_lru_tailpage vs lru_tailpage?
> 
> It's bad naming alright, but what is the wrapper for both of them
> supposed to be called then?
> 
> Note that this function is only temporary, though, that's why I did
> not spent much time on looking for a better name.
> 
> When the per-memcg lru lists finally become exclusive, this is removed
> and the function converted to work on lruvecs.
> 
> Would you be okay with just adding an /* XXX */ to the function in
> this patch that mentions that it's only temporary?

Sure. No biggie about the naming. It just hit my eyes during reading the
patch because while lru_tailpage is clear about which end of the list is
returned the memcg counterpart is not that clear.

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