Re: kswapd in tight loop 2.6.9-rc3-bk-recent

[Nick Piggin]

Andrew Morton wrote:

> Nick Piggin <piggin@xxxxxxxxxxxxxxx> wrote:
>
> > > > Ah, free_pages <= pages_high, ie. 0 <= 0, which is true;
> > >> commence spinning.
> > >>
> > >
> > >Maybe.  It requires that the zonelists be screwy:
> > >
> > > Node 1 DMA free:0kB min:0kB low:0kB high:0kB active:0kB inactive:0kB present:0kB
> > > protections[]: 0 0 0
> > > Node 1 Normal free:25272kB min:1020kB low:2040kB high:3060kB active:624172kB inactive:282700kB present:1047936kB
> > > protections[]: 0 0 0
> > > Node 1 HighMem free:0kB min:128kB low:256kB high:384kB active:0kB inactive:0kB present:0kB
> > > protections[]: 0 0 0
> > > Node 0 DMA free:728kB min:12kB low:24kB high:36kB active:788kB inactive:7848kB present:16384kB
> > > protections[]: 0 0 0
> > > Node 0 Normal free:27200kB min:1004kB low:2008kB high:3012kB active:332792kB inactive:422744kB present:1032188kB
> > > protections[]: 0 0 0
> > > Node 0 HighMem free:0kB min:128kB low:256kB high:384kB active:0kB inactive:0kB present:0kB
> > > protections[]: 0 0 0
> > >
> > >See that DMA zone on node 1?  Wonder how it got like that.  It
> > >should not be inside pgdat->nrzones anyway.
> > >
> > >
> > Oh? Why not? I didn't think empty zones were filtered out?
>
> That ininitialised zone should be outside pgdat->nr_zones, no?
>
>
> > (perhaps they should be).
>
> They will be.

I don't think the DMA side will be skipped though? Because you're
always counting down from nr_zones... That would be what it is
what it is spinning on.

> Chris, do you have time to test this, against -linus?

I think my patch would be sufficient to handle the kswapd side
(yours would be valid too, but no need to add the extra checks).

> diff -puN mm/vmscan.c~vmscan-handle-empty-zones mm/vmscan.c
> --- 25/mm/vmscan.c~vmscan-handle-empty-zones	2004-10-07 19:10:52.844797784 -0700
> +++ 25-akpm/mm/vmscan.c	2004-10-07 19:11:49.804138648 -0700
> @@ -851,6 +851,9 @@ shrink_caches(struct zone **zones, struc
> 	for (i = 0; zones[i] != NULL; i++) {
> 		struct zone *zone = zones[i];
>
> +		if (zone->present_pages == 0)
> +			continue;
> +
> 		zone->temp_priority = sc->priority;
> 		if (zone->prev_priority > sc->priority)
> 			zone->prev_priority = sc->priority;

...but could probably use something like this as well, for the
direct reclaim side.

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