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Subject[PATCH v2 13/19] mm/migrate: Use xchg instead of spinlock
Date
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.

Running SPECjbb2005 on a 4 node machine and comparing bops/JVM
JVMS LAST_PATCH WITH_PATCH %CHANGE
16 25804.1 25355.9 -1.73
1 73413 72812 -0.81

Running SPECjbb2005 on a 16 node machine and comparing bops/JVM
JVMS LAST_PATCH WITH_PATCH %CHANGE
8 101748 110199 8.30
1 170818 176303 3.21

(numbers from v1 based on v4.17-rc5)
Testcase Time: Min Max Avg StdDev
numa01.sh Real: 435.67 707.28 527.49 97.85
numa01.sh Sys: 76.41 231.19 162.49 56.13
numa01.sh User: 38247.36 59033.52 45129.31 7642.69
numa02.sh Real: 60.35 62.09 61.09 0.69
numa02.sh Sys: 15.01 30.20 20.64 5.56
numa02.sh User: 5195.93 5294.82 5240.99 40.55
numa03.sh Real: 752.04 919.89 836.81 63.29
numa03.sh Sys: 115.10 133.35 125.46 7.78
numa03.sh User: 58736.44 70084.26 65103.67 4416.10
numa04.sh Real: 418.43 709.69 512.53 104.17
numa04.sh Sys: 242.99 370.47 297.39 42.20
numa04.sh User: 34916.14 48429.54 38955.65 4928.05
numa05.sh Real: 379.27 434.05 403.70 17.79
numa05.sh Sys: 145.94 344.50 268.72 68.53
numa05.sh User: 32679.32 35449.75 33989.10 913.19

Testcase Time: Min Max Avg StdDev %Change
numa01.sh Real: 490.04 774.86 596.26 96.46 -11.5%
numa01.sh Sys: 151.52 242.88 184.82 31.71 -12.0%
numa01.sh User: 41418.41 60844.59 48776.09 6564.27 -7.47%
numa02.sh Real: 60.14 62.94 60.98 1.00 0.180%
numa02.sh Sys: 16.11 30.77 21.20 5.28 -2.64%
numa02.sh User: 5184.33 5311.09 5228.50 44.24 0.238%
numa03.sh Real: 790.95 856.35 826.41 24.11 1.258%
numa03.sh Sys: 114.93 118.85 117.05 1.63 7.184%
numa03.sh User: 60990.99 64959.28 63470.43 1415.44 2.573%
numa04.sh Real: 434.37 597.92 504.87 59.70 1.517%
numa04.sh Sys: 237.63 397.40 289.74 55.98 2.640%
numa04.sh User: 34854.87 41121.83 38572.52 2615.84 0.993%
numa05.sh Real: 386.77 448.90 417.22 22.79 -3.24%
numa05.sh Sys: 149.23 379.95 303.04 79.55 -11.3%
numa05.sh User: 32951.76 35959.58 34562.18 1034.05 -1.65%

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
---
Changelog v1->v2:
Fix stretch every interval pointed by Peter Zijlstra.

include/linux/mmzone.h | 3 ---
mm/migrate.c | 20 ++++++++++++++------
mm/page_alloc.c | 1 -
3 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index b0767703..0dbe1d5 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -669,9 +669,6 @@ struct zonelist {
struct task_struct *kcompactd;
#endif
#ifdef CONFIG_NUMA_BALANCING
- /* Lock serializing the migrate rate limiting window */
- spinlock_t numabalancing_migrate_lock;
-
/* Rate limiting time interval */
unsigned long numabalancing_migrate_next_window;

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, pgdat->numabalancing_migrate_next_window)) {
- spin_lock(&pgdat->numabalancing_migrate_lock);
- pgdat->numabalancing_migrate_nr_pages = 0;
- pgdat->numabalancing_migrate_next_window = jiffies +
- msecs_to_jiffies(migrate_interval_millisecs);
- spin_unlock(&pgdat->numabalancing_migrate_lock);
+ 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,
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8a522d2..ff8e730 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6207,7 +6207,6 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat)

pgdat_resize_init(pgdat);
#ifdef CONFIG_NUMA_BALANCING
- spin_lock_init(&pgdat->numabalancing_migrate_lock);
pgdat->numabalancing_migrate_nr_pages = 0;
pgdat->active_node_migrate = 0;
pgdat->numabalancing_migrate_next_window = jiffies;
--
1.8.3.1
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