On Mon, 8 Sep 2014 12:57:18 +0100 Mel Gorman <mgorman@xxxxxxx> wrote:
> zone_page_state is an API hazard because of the difference in behaviour
> between SMP and UP is very surprising. There is a good reason to allow
> NR_ALLOC_BATCH to go negative -- when the counter is reset the negative
> value takes recent activity into account. This patch makes zone_page_state
> behave the same on SMP and UP as saving one branch on UP is not likely to
> make a measurable performance difference.
>
> ...
>
> --- a/include/linux/vmstat.h
> +++ b/include/linux/vmstat.h
> @@ -131,10 +131,8 @@ static inline unsigned long zone_page_state(struct zone *zone,
> enum zone_stat_item item)
> {
> long x = atomic_long_read(&zone->vm_stat[item]);
> -#ifdef CONFIG_SMP
> if (x < 0)
> x = 0;
> -#endif
> return x;
> }
We now have three fixes for the same thing. I'm presently holding on
to hannes's mm-page_alloc-fix-zone-allocation-fairness-on-up.patch.
Regularizing zone_page_state() in this fashion seems a good idea and is
presumably safe because callers have been tested with SMP. So unless
shouted at I think I'll queue this one for 3.18?
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