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Date: Wed, 18 Jul 2001 19:14:07 -0300 (BRT)
From: Marcelo Tosatti <marcelo@conectiva.com.br>
To: Linus Torvalds <torvalds@transmeta.com>
Cc: lkml <linux-kernel@vger.kernel.org>, Rik van Riel <riel@conectiva.com.br>
Subject: Re: Inclusion of zoned inactive/free shortage patch 
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On Wed, 18 Jul 2001, Marcelo Tosatti wrote:

> 
> 
> On Wed, 18 Jul 2001, Linus Torvalds wrote:
> 
> > 
> > On Wed, 18 Jul 2001, Marcelo Tosatti wrote:
> > > >
> > > > Cool.
> > > >
> > > > Willing to write a patch and give it some preliminary testing?
> > >
> > > Sure. However its not _that_ easy. We do have a global inactive target.
> > 
> > Absolutely. But this is why it's easier to have the more relaxed
> > constraints - we have to make sure that the global inactive target is
> > clearly lower than the sum of the relaxed local targets.
> > 
> > That way, whenever there is a global inactive need, we _clearly_ have one
> > or more zones (usually _all_ of them with any reasonably balanced system:
> > and note how this whole logic will strive to _add_ balance) that will
> > trigger the test, and there is no worry that we get into the nasty case
> > where we suddenly start to try to overly cannibalize one zone horribly.
> > 
> > > There is no perzone inactive shortage, which is needed to calculate
> > > "zone_inactive_plenty()".
> > 
> > Right. But the gobal inactivity shortage can certainly be a clue to how to
> > do this.
> > 
> > So when the global shortage is effectively
> > 
> > MAX of
> > 
> > 	(freepages.high + inactive_target) - nr_free_pages - inactive_clean - inactive_dirty
> > 
> > or
> > 
> > 	per-zone shortage.
> > 
> > So for this discussion we can ignore the per-zone shortage case (because
> > _obviously_ the per-zone "inactive_plenty()" cannot be a shortage of
> > inactive ;), and only concentrate on making sure that the sum of the
> > per-zone inactive_plenty decisions is noticeably more than the global
> > shortage (for example, by a factor of two, or something like that). So one
> > suggestion would be to take the same logic as the global shortage, but
> > apply it to just the local zone, and then multiply by two (as the slop to
> > make sure that we don't every under-estimate).
> > 
> > So something like
> > 
> >     inactive_plenty(zone)
> >     {
> > 	if (!zone->nrpages)
> > 		return 0;
> > 	shortage = zone->pages_high;
> > 	shortage -= zone->inactive_dirty_pages;
> > 	shortage -= zone->inactive_clean_pages;
> > 	shortage -= zone->free_pages;
> > 
> > 	/* zone inactive-target is 1/2 of the number of pages */
> > 	return shortage < zone->nrpages / 2;
> >     }
> 
> Wait. Don't you mean:
> 
> 	/* True if we have enough inactive pages for this zone */
> 	
> 	inactive_plenty(zone)
> 	{
> 		if (!zone->nrpages)
> 			return 0;
> 		inactive = zone->inactive_dirty_pages;
> 		inactive += zone->inactive_clean_pages;
> 		inactive += zone->free_pages
> 		
> 		return (inactive < zone->nrpages / 2); 
				^^ 
Err I mean		 	 > 

> 	}
> 
> ? 

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