Hi Johaness, On Tue, Sep 9, 2014 at 4:15 PM, Johannes Weiner wrote: > The zone allocation batches can easily underflow due to higher-order > allocations or spills to remote nodes. On SMP that's fine, because > underflows are expected from concurrency and dealt with by returning > 0. But on UP, zone_page_state will just return a wrapped unsigned > long, which will get past the <= 0 check and then consider the zone > eligible until its watermarks are hit. > > 3a025760fc15 ("mm: page_alloc: spill to remote nodes before waking > kswapd") already made the counter-resetting use atomic_long_read() to > accomodate underflows from remote spills, but it didn't go all the way > with it. Make it clear that these batches are expected to go negative > regardless of concurrency, and use atomic_long_read() everywhere. > > Fixes: 81c0a2bb515f ("mm: page_alloc: fair zone allocator policy") > Reported-by: Vlastimil Babka > Reported-by: Leon Romanovsky > Signed-off-by: Johannes Weiner > Acked-by: Mel Gorman > Cc: "3.12+" > --- > mm/page_alloc.c | 7 +++---- > 1 file changed, 3 insertions(+), 4 deletions(-) > > Sorry I forgot to CC you, Leon. Resend with updated Tags. > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 18cee0d4c8a2..eee961958021 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1612,7 +1612,7 @@ again: > } > > __mod_zone_page_state(zone, NR_ALLOC_BATCH, -(1 << order)); > - if (zone_page_state(zone, NR_ALLOC_BATCH) == 0 && > + if (atomic_long_read(&zone->vm_stat[NR_ALLOC_BATCH]) <= 0 && > !zone_is_fair_depleted(zone)) > zone_set_flag(zone, ZONE_FAIR_DEPLETED); > > @@ -5701,9 +5701,8 @@ static void __setup_per_zone_wmarks(void) > zone->watermark[WMARK_HIGH] = min_wmark_pages(zone) + (tmp > >> 1); > > __mod_zone_page_state(zone, NR_ALLOC_BATCH, > - high_wmark_pages(zone) - > - low_wmark_pages(zone) - > - zone_page_state(zone, > NR_ALLOC_BATCH)); > + high_wmark_pages(zone) - low_wmark_pages(zone) - > + atomic_long_read(&zone->vm_stat[NR_ALLOC_BATCH])); > > setup_zone_migrate_reserve(zone); > spin_unlock_irqrestore(&zone->lock, flags); > I think the better way will be to apply Mel's patch https://lkml.org/lkml/2014/9/8/214 which fix zone_page_state shadow casting issue and convert all atomic_long_read(&zone->vm_stat[NR_ALLOC_BATCH])) to zone_page__state(zone, NR_ALLOC_BATCH). This move will unify access to vm_stat. > -- > 2.0.4 > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org > -- Leon Romanovsky | Independent Linux Consultant www.leon.nu | leon@leon.nu