Re: [PATCH] kswapd shall not sleep during page shortage

[Marcelo Tosatti <marcelo.tosatti@cyclades.com>]

On Tue, Nov 09, 2004 at 12:19:45PM -0800, Andrew Morton wrote:
> Marcelo Tosatti <marcelo.tosatti@cyclades.com> wrote:
> >
> > 
> > Andrew,
> > 
> > I was wrong last time I read balance_pgdat() when I thought kswapd
> > couldnt sleep under page shortage. 
> > 
> > It can, because all_zones_ok is set to "1" inside the 
> > "priority=DEF_PRIORITY; priority >= 0; priority--" loop.
> > 
> > So this patch sets "all_zones_ok" to zero even if all_unreclaimable 
> > is set, avoiding it from sleeping when zones are under page short.
> > 
> 
> Does this solve any observed problem?  What testing was done, and what were
> the results??


The observed problem are the page allocation failures!

No testing has been done, but it is an obvious problem if you read the
code. 

What your thinking?


> > --- linux-2.6.10-rc1-mm2/mm/vmscan.c.orig	2004-11-09 16:38:04.480873424 -0200
> > +++ linux-2.6.10-rc1-mm2/mm/vmscan.c	2004-11-09 16:38:08.624243536 -0200
> > @@ -1033,15 +1033,17 @@
> >  				if (zone->present_pages == 0)
> >  					continue;
> >  
> > -				if (zone->all_unreclaimable &&
> > -						priority != DEF_PRIORITY)
> > -					continue;
> > -
> >  				if (!zone_watermark_ok(zone, order,
> >  						zone->pages_high, 0, 0, 0)) {
> >  					end_zone = i;
> > -					goto scan;
> > +					all_zones_ok = 0;
> >  				}
> > +
> > +				if (zone->all_unreclaimable &&
> > +						priority != DEF_PRIORITY)
> > +					continue;
> > +
> > +				goto scan;
> >  			}
> >  			goto out;
> >  		} else {
--
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