On Tue, Aug 17, 2010 at 11:26:05AM +0900, Minchan Kim wrote:
> On Tue, Aug 17, 2010 at 1:06 AM, Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
> > [npiggin@xxxxxxx bounces, switched to yahoo address]
> >
> > On Mon, Aug 16, 2010 at 10:43:50AM +0100, Mel Gorman wrote:
>
> <snip>
>
> >> + * potentially causing a live-lock. While kswapd is awake and
> >> + * free pages are low, get a better estimate for free pages
> >> + */
> >> + if (nr_free_pages < zone->percpu_drift_mark &&
> >> + !waitqueue_active(&zone->zone_pgdat->kswapd_wait)) {
> >> + int cpu;
> >> +
> >> + for_each_online_cpu(cpu) {
> >> + struct per_cpu_pageset *pset;
> >> +
> >> + pset = per_cpu_ptr(zone->pageset, cpu);
> >> + nr_free_pages += pset->vm_stat_diff[NR_FREE_PAGES];
>
> We need to consider CONFIG_SMP.
>
We do.
#ifdef CONFIG_SMP
unsigned long zone_nr_free_pages(struct zone *zone);
#else
#define zone_nr_free_pages(zone) zone_page_state(zone, NR_FREE_PAGES)
#endif /* CONFIG_SMP */
and a wrapping of CONFIG_SMP around the function in mmzone.c .
> >> + }
> >> + }
> >> +
> >> + return nr_free_pages;
> >> +}
> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> >> index c2407a4..67a2ed0 100644
> >> --- a/mm/page_alloc.c
> >> +++ b/mm/page_alloc.c
> >> @@ -1462,7 +1462,7 @@ int zone_watermark_ok(struct zone *z, int order, unsigned long mark,
> >> {
> >> /* free_pages my go negative - that's OK */
> >> long min = mark;
> >> - long free_pages = zone_page_state(z, NR_FREE_PAGES) - (1 << order) + 1;
> >> + long free_pages = zone_nr_free_pages(z) - (1 << order) + 1;
> >> int o;
> >>
> >> if (alloc_flags & ALLOC_HIGH)
> >> @@ -2413,7 +2413,7 @@ void show_free_areas(void)
> >> " all_unreclaimable? %s"
> >> "\n",
> >> zone->name,
> >> - K(zone_page_state(zone, NR_FREE_PAGES)),
> >> + K(zone_nr_free_pages(zone)),
> >> K(min_wmark_pages(zone)),
> >> K(low_wmark_pages(zone)),
> >> K(high_wmark_pages(zone)),
> >> diff --git a/mm/vmstat.c b/mm/vmstat.c
> >> index 7759941..c95a159 100644
> >> --- a/mm/vmstat.c
> >> +++ b/mm/vmstat.c
> >> @@ -143,6 +143,9 @@ static void refresh_zone_stat_thresholds(void)
> >> for_each_online_cpu(cpu)
> >> per_cpu_ptr(zone->pageset, cpu)->stat_threshold
> >> = threshold;
> >> +
> >> + zone->percpu_drift_mark = high_wmark_pages(zone) +
> >> + num_online_cpus() * threshold;
> >> }
> >> }
> >
> > Hm, this one I don't quite get (might be the jetlag, though): we have
> > _at least_ NR_FREE_PAGES free pages, there may just be more lurking in
>
> We can't make sure it.
> As I said previous mail, current allocation path decreases
> NR_FREE_PAGES after it removes pages from buddy list.
>
> > the pcp counters.
> >
> > So shouldn't we only collect the pcp deltas in case the high watermark
> > is breached? Above this point, we should be fine or better, no?
>
> If we don't consider allocation path, I agree on Hannes's opinion.
> At least, we need to listen why Mel determine the threshold. :)
>
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
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