Re: [PATCH] total_free_shortage() using zone_free_shortage()

[Marcelo Tosatti]

On Wed, 8 Aug 2001, Linus Torvalds wrote:

> 
> [ Hey, I can have long discussions by myself. I don't need you guys to
>   answer me at all.
> 
>   This must be what senility feels like. Linus "doddering fool" Torvalds ]
> 
> On Tue, 7 Aug 2001, Linus Torvalds wrote:
> >
> > We should really document the ranges clearly. Right now (with these
> > changes), the ranges would be (with users in parenthesis):
> >
> >  free (free + inactive_clean):
> >
> > 	low water mark: zone->pages_high	(__alloc_pages, zone_free_shortage)
> > 	high water mark: zone->pages_high*2	(zone_free_plenty)
> 
> That's subtly wrong, __alloc_pages really has "zone->pages_low", not
> "pages_high"  as the low water mark on when to start kswapd.
> 
> It does use "pages_high" too - but it is used as a "prefer this zone
> because it isn't close to empty" marker. In short, it's really more of a
> local high water mark.
> 
> So the free_shortage() logic really should be:
>  - we want zone to have "pages_high" on _average_, but it's a shortage
>    only if any zone is under the "pages_low" thing.

I think you are misunderstanding things here.

Having "zone->pages_low" as the low water mark to when start kswapd does
_not_ mean we want "zone->pages_low" as the freetarget (or the "free
shortage" indicator). 

Could you be more verbose ?