linux-kernel - Re: [PATCH] shrink_all_memory() use sc.nr

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Date:	Wed, 11 Feb 2009 21:43:24 +0900
From:	MinChan Kim <minchan.kim@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	MinChan Kim <minchan.kim@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Rik van Riel <riel@...hat.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	William Lee Irwin III <wli@...ementarian.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] shrink_all_memory() use sc.nr_reclaimed

On Wed, 11 Feb 2009 20:50:37 +0900 (JST)
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:

> > On Wed, Feb 11, 2009 at 05:41:21AM +0900, KOSAKI Motohiro wrote:
> > > >>  {
> > > >>       struct zone *zone;
> > > >> -     unsigned long nr_to_scan, ret = 0;
> > > >> +     unsigned long nr_to_scan;
> > > >>       enum lru_list l;
> > > >
> > > > Basing it on swsusp-clean-up-shrink_all_zones.patch probably makes it
> > > > easier for Andrew to pick it up.
> > > 
> > > ok, thanks.
> > > 
> > > >>                       reclaim_state.reclaimed_slab = 0;
> > > >> -                     shrink_slab(nr_pages, sc.gfp_mask, global_lru_pages());
> > > >> -                     ret += reclaim_state.reclaimed_slab;
> > > >> -             } while (ret < nr_pages && reclaim_state.reclaimed_slab > 0);
> > > >> +                     shrink_slab(nr_pages, sc.gfp_mask,
> > > >> +                                 global_lru_pages());
> > > >> +                     sc.nr_reclaimed += reclaim_state.reclaimed_slab;
> > > >> +             } while (sc.nr_reclaimed < nr_pages &&
> > > >> +                      reclaim_state.reclaimed_slab > 0);
> > > >
> > > > :(
> > > >
> > > > Is this really an improvement?  `ret' is better to read than
> > > > `sc.nr_reclaimed'.
> > > 
> > > I know it's debetable thing.
> > > but I still think code consistency is important than variable name preference.
> > 
> > How about this ?
> > 
> > I followed do_try_to_free_pages coding style.
> > It use both 'sc->nr_reclaimed' and 'ret'.
> > It can support code consistency and readability. 
> > 
> > So, I think it would be better.  
> > If you don't mind, I will resend with your sign-off.
> 
> looks good. thanks.
> 
> 
> > -static unsigned long shrink_all_zones(unsigned long nr_pages, int prio,
> > +static void shrink_all_zones(unsigned long nr_pages, int prio,
> >  				      int pass, struct scan_control *sc)
> >  {
> >  	struct zone *zone;
> >  	unsigned long nr_to_scan, ret = 0;
> > +	unsigned long nr_reclaimed = sc->nr_reclaimed;
> >  	enum lru_list l;
> 
> and, please changelog change.
> this patch have behavior change.
> 
> old bale-out checking didn't checked properly.
> it's because shrink_all_memory() has five pass. but shrink_all_zones()
> initialize ret = 0 every time.
> 
> then, at pass 1-4, if(ret >= nr_pages) don't judge reclaimed enough page or not.
> 

Hmm, I think old bale-out code is right. 
In shrink_all_memory, As more reclaiming with pass progressing, 
the smaller nr_to_scan is. The nr_to_scan is the number of page shrinking which
user want. 
The shrink_all_zones have to reclaim nr_to_scan's page by doing best effort.
So, If you use accumulation of reclaim, it can break bale-out in shrink_all_zones.
I mean here.

'
              NR_LRU_BASE + l)); 
        ret += shrink_list(l, nr_to_scan, zone,
                sc, prio);
        if (ret >= nr_pages)
          return ret; 
      }    
'

I have to make patch again so that it will keep on old bale-out behavior. 

-- 
Kinds Regards
MinChan Kim
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