Messages in this thread | | | Date | Mon, 24 Jul 2017 14:50:15 +0200 | From | Michal Hocko <> | Subject | Re: [PATCH 3/4] mm, page_owner: don't grab zone->lock for init_pages_in_zone() |
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On Thu 20-07-17 15:40:28, Vlastimil Babka wrote: > init_pages_in_zone() is run under zone->lock, which means a long lock time and > disabled interrupts on large machines. This is currently not an issue since it > runs early in boot, but a later patch will change that. > However, like other pfn scanners, we don't actually need zone->lock even when > other cpus are running. The only potentially dangerous operation here is > reading bogus buddy page owner due to race, and we already know how to handle > that. The worse that can happen is that we skip some early allocated pages, > which should not affect the debugging power of page_owner noticeably.
Makes sense to me
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
> --- > mm/page_owner.c | 16 ++++++++++------ > 1 file changed, 10 insertions(+), 6 deletions(-) > > diff --git a/mm/page_owner.c b/mm/page_owner.c > index 5aa21ca237d9..cf6568d1dc14 100644 > --- a/mm/page_owner.c > +++ b/mm/page_owner.c > @@ -567,11 +567,17 @@ static void init_pages_in_zone(pg_data_t *pgdat, struct zone *zone) > continue; > > /* > - * We are safe to check buddy flag and order, because > - * this is init stage and only single thread runs. > + * To avoid having to grab zone->lock, be a little > + * careful when reading buddy page order. The only > + * danger is that we skip too much and potentially miss > + * some early allocated pages, which is better than > + * heavy lock contention. > */ > if (PageBuddy(page)) { > - pfn += (1UL << page_order(page)) - 1; > + unsigned long order = page_order_unsafe(page); > + > + if (order > 0 && order < MAX_ORDER) > + pfn += (1UL << order) - 1; > continue; > } > > @@ -590,6 +596,7 @@ static void init_pages_in_zone(pg_data_t *pgdat, struct zone *zone) > __set_page_owner_init(page_ext, init_handle); > count++; > } > + cond_resched(); > } > > pr_info("Node %d, zone %8s: page owner found early allocated %lu pages\n", > @@ -600,15 +607,12 @@ static void init_zones_in_node(pg_data_t *pgdat) > { > struct zone *zone; > struct zone *node_zones = pgdat->node_zones; > - unsigned long flags; > > for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) { > if (!populated_zone(zone)) > continue; > > - spin_lock_irqsave(&zone->lock, flags); > init_pages_in_zone(pgdat, zone); > - spin_unlock_irqrestore(&zone->lock, flags); > } > } > > -- > 2.13.2
-- Michal Hocko SUSE Labs
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