(2012/06/27 16:51), Minchan Kim wrote: > When hotplug offlining happens on zone A, it starts to mark freed page > as MIGRATE_ISOLATE type in buddy for preventing further allocation. > (MIGRATE_ISOLATE is very irony type because it's apparently on buddy > but we can't allocate them). > When the memory shortage happens during hotplug offlining, > current task starts to reclaim, then wake up kswapd. > Kswapd checks watermark, then go sleep because current zone_watermark_ok_safe > doesn't consider MIGRATE_ISOLATE freed page count. > Current task continue to reclaim in direct reclaim path without kswapd's helping. > The problem is that zone->all_unreclaimable is set by only kswapd > so that current task would be looping forever like below. > > __alloc_pages_slowpath > restart: > wake_all_kswapd > rebalance: > __alloc_pages_direct_reclaim > do_try_to_free_pages > if global_reclaim && !all_unreclaimable > return 1; /* It means we did did_some_progress */ > skip __alloc_pages_may_oom > should_alloc_retry > goto rebalance; > > If we apply KOSAKI's patch[1] which doesn't depends on kswapd > about setting zone->all_unreclaimable, we can solve this problem > by killing some task in direct reclaim path. But it doesn't wake up kswapd, still. > It could be a problem still if other subsystem needs GFP_ATOMIC request. > So kswapd should consider MIGRATE_ISOLATE when it calculate free pages > BEFORE going sleep. > > This patch counts the number of MIGRATE_ISOLATE page block and > zone_watermark_ok_safe will consider it if the system has such blocks > (fortunately, it's very rare so no problem in POV overhead and kswapd is never > hotpath). > > Copy/modify from Mel's quote > " > Ideal solution would be "allocating" the pageblock. > It would keep the free space accounting as it is but historically, > memory hotplug didn't allocate pages because it would be difficult to > detect if a pageblock was isolated or if part of some balloon. > Allocating just full pageblocks would work around this, However, > it would play very badly with CMA. > " > > [1] http://lkml.org/lkml/2012/6/14/74 > > * from v1 > - add changelog > - make functions simple > - remove atomic variable > - discard exact isolated free page accounting. > - rebased on next-20120626 > > Suggested-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > Cc: Aaditya Kumar <aaditya.kumar.30@xxxxxxxxx> > Cc: Mel Gorman <mgorman@xxxxxxx> > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> > --- > > Aaditya, coul you confirm this patch solve your problem and > make sure nr_pageblock_isolate is zero after hotplug end? > > Thanks! > > include/linux/mmzone.h | 8 ++++++++ > mm/page_alloc.c | 31 +++++++++++++++++++++++++++++++ > mm/page_isolation.c | 29 +++++++++++++++++++++++++++-- > 3 files changed, 66 insertions(+), 2 deletions(-) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index dbc876e..6ee83b8 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -474,6 +474,14 @@ struct zone { > * rarely used fields: > */ > const char *name; > +#ifdef CONFIG_MEMORY_ISOLATION > + /* > + * the number of MIGRATE_ISOLATE *pageblock*. > + * We need this for free page counting. Look at zone_watermark_ok_safe. > + * It's protected by zone->lock > + */ > + int nr_pageblock_isolate; > +#endif > } ____cacheline_internodealigned_in_smp; > > typedef enum { > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index c175fa9..b12c8ec 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -218,6 +218,11 @@ EXPORT_SYMBOL(nr_online_nodes); > > int page_group_by_mobility_disabled __read_mostly; > > +/* > + * NOTE: > + * Don't use set_pageblock_migratetype(page, MIGRATE_ISOLATE) directly. > + * Instead, use {un}set_pageblock_isolate. > + */ > void set_pageblock_migratetype(struct page *page, int migratetype) > { > if (unlikely(page_group_by_mobility_disabled)) > @@ -1614,6 +1619,23 @@ static bool __zone_watermark_ok(struct zone *z, int order, unsigned long mark, > return true; > } > > +#ifdef CONFIG_MEMORY_ISOLATION > +static inline unsigned long nr_zone_isolate_freepages(struct zone *zone) > +{ > + unsigned long nr_pages = 0; > + > + if (unlikely(zone->nr_pageblock_isolate)) { > + nr_pages = zone->nr_pageblock_isolate * pageblock_nr_pages; > + } > + return nr_pages; > +} > +#else > +static inline unsigned long nr_zone_isolate_freepages(struct zone *zone) > +{ > + return 0; > +} > +#endif > + > bool zone_watermark_ok(struct zone *z, int order, unsigned long mark, > int classzone_idx, int alloc_flags) > { > @@ -1629,6 +1651,14 @@ bool zone_watermark_ok_safe(struct zone *z, int order, unsigned long mark, > if (z->percpu_drift_mark && free_pages < z->percpu_drift_mark) > free_pages = zone_page_state_snapshot(z, NR_FREE_PAGES); > > + /* > + * If the zone has MIGRATE_ISOLATE type free page, > + * we should consider it. nr_zone_isolate_freepages is never > + * accurate so kswapd might not sleep although she can. > + * But it's more desirable for memory hotplug rather than > + * forever sleep which cause livelock in direct reclaim path. > + */ > + free_pages -= nr_zone_isolate_freepages(z); Here, free_pages could be < 0 ? Thanks, -Kame -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>