On Tue, 7 Aug 2001, Linus Torvalds wrote:
>
> On Tue, 7 Aug 2001, Linus Torvalds wrote:
> >
> > The current patch "zone_free_plenty()" logic also happens to be just at
> > the corner of what __alloc_pages() thinks is good, so the anti-hysteresis
> > doesn't actually end up working in that sense - we end up bouncing around
> > that magic "pages_high" value.
>
> The same, it seems, is true of "total_free_shortage()", and the zone
> "pages_low" corner.
>
> We start up kswapd when the free count shrinks below "pages_low", so we
> should keep kswapd running for longer than that, and I think your version
> of "zone_free_shortage()" was thus the better one - using pages_high as
> the point where we no longer think there is a shortage.
>
> We should really document the ranges clearly. Right now (with these
> changes), the ranges would be (with users in parenthesis):
>
> inactive (free + inactive_clean + inactive_dirty):
>
> low water mark: zone->pages_high (zone_inactive_shortage, total_inactive_shortage)
> high water mark: zone->size / 3 (zone_inactive_plenty)
>
> 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)
>
> reclaim (free):
>
> low water mark: zone->pages_min (__alloc_pages)
> high water mark: zone->pages_low (kreclaimd)
>
> and they now sem to (a) always have a nice hysteresis region (ie low is
> clearly smaller than high, once the free+inactive_clean case has been
> fixed) and (b) the different low/high water mark users seem to agree.
>
> Looks reasonably sane to me. Can anybody find a case where we use
> conflicting low/high watermarks?
No, I think its ok.
But we still allow a certain zone from staying in a critical shortage for
a long period of time. It can (and used to, before the zoned approach
code) trigger OOM deadlocks.
I'll check if I can do happen in practice with the "pages_high*2" changes.
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This archive was generated by hypermail 2b29 : Wed Aug 15 2001 - 21:00:15 EST