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

Marcelo Tosatti (marcelo@conectiva.com.br)
Wed, 8 Aug 2001 02:46:52 -0300 (BRT)


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 ?

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