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Subject[PATCH 2/6] mm/migrate: Use trylock while resetting rate limit
Date
Since this spinlock will only serialize migrate rate limiting,
convert the spinlock to a trylock. If another task races ahead of this task
then this task can simply move on.

While here, add correct two abnormalities.
- Avoid time being stretched for every interval.
- Use READ/WRITE_ONCE with next window.

specjbb2005 / bops/JVM / higher bops are better
on 2 Socket/2 Node Intel
JVMS Prev Current %Change
4 206350 200892 -2.64502
1 319963 325766 1.81365


on 2 Socket/2 Node Power9 (PowerNV)
JVMS Prev Current %Change
4 186539 190261 1.99529
1 220344 195305 -11.3636


on 4 Socket/4 Node Power7
JVMS Prev Current %Change
8 56836 57651.1 1.43413
1 112970 111351 -1.43312


dbench / transactions / higher numbers are better
on 2 Socket/2 Node Intel
count Min Max Avg Variance %Change
5 13136.1 13170.2 13150.2 14.7482
5 12254.7 12331.9 12297.8 28.1846 -6.48203


on 2 Socket/4 Node Power8 (PowerNV)
count Min Max Avg Variance %Change
5 4319.79 4998.19 4836.53 261.109
5 4997.83 5030.14 5015.54 12.947 3.70121


on 2 Socket/2 Node Power9 (PowerNV)
count Min Max Avg Variance %Change
5 9325.56 9402.7 9362.49 25.9638
5 9331.84 9375.11 9352.04 16.0703 -0.111616


on 4 Socket/4 Node Power7
count Min Max Avg Variance %Change
5 132.581 191.072 170.554 21.6444
5 147.55 181.605 168.963 11.3513 -0.932842

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
---
Changelog v1->v2:
Fix stretch every interval pointed by Peter Zijlstra.
Verified that some of the regression is due to fixing interval stretch.

mm/migrate.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 8c0af0f..dbc2cb7 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1868,16 +1868,24 @@ 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)) {
- spin_lock(&pgdat->numabalancing_migrate_lock);
+ if (time_after(jiffies, next_window) &&
+ spin_trylock(&pgdat->numabalancing_migrate_lock)) {
pgdat->numabalancing_migrate_nr_pages = 0;
- pgdat->numabalancing_migrate_next_window = jiffies +
- msecs_to_jiffies(migrate_interval_millisecs);
+ do {
+ next_window += interval;
+ } while (unlikely(time_after(jiffies, next_window)));
+
+ WRITE_ONCE(pgdat->numabalancing_migrate_next_window, next_window);
spin_unlock(&pgdat->numabalancing_migrate_lock);
}
if (pgdat->numabalancing_migrate_nr_pages > ratelimit_pages) {
--
1.8.3.1
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