Limit max scan fraction to 1/64. The scan fractions will be
1/4096, 64x1/2048, 64x1/1024, ..., 64x1/64
The old ones are
1/4096, 1/2048, 1/1024, ..., 1/1
which is too much to create major imbalance of aging rates.
Signed-off-by: Wu Fengguang <[email protected]>
---
include/linux/mmzone.h | 9 ++++++---
mm/vmscan.c | 18 ++++++++++++------
2 files changed, 18 insertions(+), 9 deletions(-)
--- linux.orig/include/linux/mmzone.h
+++ linux/include/linux/mmzone.h
@@ -251,10 +251,13 @@ struct zone {
/*
* The "priority" of VM scanning is how much of the queues we will scan in one
- * go. A value of 12 for DEF_PRIORITY implies that we will scan 1/4096th of the
- * queues ("queue_length >> 12") during an aging round.
+ * go. A value of 12 for DEF_PRIORITY/PRIORITY_STEPS implies that we will
+ * scan 1/4096th of the queues ("queue_length >> 12") during an aging round.
+ * Typically we will first try to scan 1/4096, then 64 times 1/2048, then 64
+ * times 1/1024, ..., at last 64 times 1/64.
*/
-#define DEF_PRIORITY 12
+#define PRIORITY_STEPS 64
+#define DEF_PRIORITY (12*PRIORITY_STEPS)
/*
* One allocation request operates on a zonelist. A zonelist
--- linux.orig/mm/vmscan.c
+++ linux/mm/vmscan.c
@@ -1006,7 +1006,7 @@ refill_inactive_zone(struct zone *zone,
* `distress' is a measure of how much trouble we're having reclaiming
* pages. 0 -> no problems. 100 -> great trouble.
*/
- distress = 100 >> zone->prev_priority;
+ distress = 100 >> (zone->prev_priority / PRIORITY_STEPS);
/*
* The point of this algorithm is to decide when to start reclaiming
@@ -1128,7 +1128,8 @@ shrink_zone(struct zone *zone, struct sc
* slowly sift through the active list.
*/
nr_active = zone->nr_scan_active + 1;
- nr_inactive = (zone->nr_inactive >> sc->priority) + SWAP_CLUSTER_MAX;
+ nr_inactive = ((zone->nr_inactive / PRIORITY_STEPS) >>
+ (sc->priority / PRIORITY_STEPS)) + SWAP_CLUSTER_MAX;
nr_inactive &= ~(SWAP_CLUSTER_MAX - 1);
sc->nr_to_scan = SWAP_CLUSTER_MAX;
@@ -1265,8 +1266,13 @@ int try_to_free_pages(struct zone **zone
zone->temp_priority = DEF_PRIORITY;
}
- /* The added 10 priorities are for scan rate balancing */
- for (priority = DEF_PRIORITY + 10; priority >= 0; priority--) {
+ /*
+ * The first PRIORITY_STEPS priorities are for scan rate balancing.
+ * One run of shrink_zone() can create at most 1/64 imbalance, here
+ * we first scan about 64 times 1/4096 for aging, just enough to
+ * rebalance it, before creating new imbalance.
+ */
+ for (priority = DEF_PRIORITY + PRIORITY_STEPS; priority >= 0; priority--) {
sc.nr_mapped = read_page_state(nr_mapped);
sc.nr_scanned = 0;
sc.nr_reclaimed = 0;
@@ -1301,7 +1307,7 @@ int try_to_free_pages(struct zone **zone
}
/* Take a nap, wait for some writeback to complete */
- if (sc.nr_scanned && priority < DEF_PRIORITY)
+ if (sc.nr_scanned && priority < DEF_PRIORITY - PRIORITY_STEPS)
blk_congestion_wait(WRITE, HZ/10);
}
out:
@@ -1464,7 +1470,7 @@ scan_swspd:
* OK, kswapd is getting into trouble. Take a nap, then take
* another pass across the zones.
*/
- if (total_scanned && priority < DEF_PRIORITY - 2)
+ if (total_scanned && priority < DEF_PRIORITY - PRIORITY_STEPS)
blk_congestion_wait(WRITE, HZ/10);
/*
--