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authorMel Gorman <mgorman@suse.de>2014-01-22 03:50:59 +0400
committerLinus Torvalds <torvalds@linux-foundation.org>2014-01-22 04:19:48 +0400
commit1c5e9c27cbd966c7f0038698d5dcd5ada3574f47 (patch)
treea546cec0019aa3b726ba06e50ce38f960ee8f222 /mm/migrate.c
parent1c30e0177e4f41a11cb88b0f1f056ccebfe0fff4 (diff)
downloadlinux-1c5e9c27cbd966c7f0038698d5dcd5ada3574f47.tar.xz
mm: numa: limit scope of lock for NUMA migrate rate limiting
NUMA migrate rate limiting protects a migration counter and window using a lock but in some cases this can be a contended lock. It is not critical that the number of pages be perfect, lost updates are acceptable. Reduce the importance of this lock. Signed-off-by: Mel Gorman <mgorman@suse.de> Reviewed-by: Rik van Riel <riel@redhat.com> Cc: Alex Thorlton <athorlton@sgi.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/migrate.c')
-rw-r--r--mm/migrate.c21
1 files changed, 12 insertions, 9 deletions
diff --git a/mm/migrate.c b/mm/migrate.c
index 41eba21f10ba..4612bb2e3677 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1602,26 +1602,29 @@ bool migrate_ratelimited(int node)
static bool numamigrate_update_ratelimit(pg_data_t *pgdat,
unsigned long nr_pages)
{
- bool rate_limited = false;
-
/*
* 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!
*/
- spin_lock(&pgdat->numabalancing_migrate_lock);
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 (pgdat->numabalancing_migrate_nr_pages > ratelimit_pages)
- rate_limited = true;
- else
- pgdat->numabalancing_migrate_nr_pages += nr_pages;
- spin_unlock(&pgdat->numabalancing_migrate_lock);
-
- return rate_limited;
+ return true;
+
+ /*
+ * This is an unlocked non-atomic update so errors are possible.
+ * The consequences are failing to migrate when we potentiall should
+ * have which is not severe enough to warrant locking. If it is ever
+ * a problem, it can be converted to a per-cpu counter.
+ */
+ pgdat->numabalancing_migrate_nr_pages += nr_pages;
+ return false;
}
static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)