Messages in this thread | | | Date | Mon, 23 Jul 2018 12:54:38 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 13/19] mm/migrate: Use xchg instead of spinlock |
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On Wed, Jun 20, 2018 at 10:32:54PM +0530, Srikar Dronamraju wrote: > Currently resetting the migrate rate limit is under a spinlock. > The spinlock will only serialize the migrate rate limiting and something > similar can actually be achieved by a simpler xchg.
You're again not explaining things right. The xchg isn't simpler in any way. It just happens to be faster, esp. so on PPC.
> diff --git a/mm/migrate.c b/mm/migrate.c > index 8c0af0f..c774990 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1868,17 +1868,25 @@ static struct page *alloc_misplaced_dst_page(struct page *page, > static bool numamigrate_update_ratelimit(pg_data_t *pgdat, > unsigned long nr_pages) > { > + unsigned long next_window, interval; > + > + next_window = READ_ONCE(pgdat->numabalancing_migrate_next_window); > + interval = msecs_to_jiffies(migrate_interval_millisecs); > + > /* > * Rate-limit the amount of data that is being migrated to a node. > * Optimal placement is no good if the memory bus is saturated and > * all the time is being spent migrating! > */ > + if (time_after(jiffies, next_window)) { > + if (xchg(&pgdat->numabalancing_migrate_nr_pages, 0)) { > + do { > + next_window += interval; > + } while (unlikely(time_after(jiffies, next_window))); > + > + WRITE_ONCE(pgdat->numabalancing_migrate_next_window, > + next_window); > + } > } > if (pgdat->numabalancing_migrate_nr_pages > ratelimit_pages) { > trace_mm_numa_migrate_ratelimit(current, pgdat->node_id,
If you maybe write that like:
if (time_after(jiffies, next_window) && xchg(&pgdat->numabalancing_migrate_nr_pages, 0UL)) {
do { next_window += interval; } while (unlikely(time_after(jiffies, next_window)));
WRITE_ONCE(pgdat->numabalancing_migrate_next_window, next_window); }
Then you avoid an indent level and line-wrap, resulting imo easier to read code.
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