When the allocator enters its slow path, kswapd is woken up to balance the
node. It continues working until all zones within the node are balanced. For
order-0 allocations, this makes perfect sense but for higher orders it can
have unintended side-effects. If the zone sizes are imbalanced, kswapd
may reclaim heavily on a smaller zone discarding an excessive number of
pages. The user-visible behaviour is that kswapd is awake and reclaiming
even though plenty of pages are free from a suitable zone.
This patch alters the "balance" logic to stop kswapd if any suitable zone
becomes balanced to reduce the number of pages it reclaims from other zones.
Signed-off-by: Mel Gorman <mel@xxxxxxxxx>
---
include/linux/mmzone.h | 3 ++-
mm/page_alloc.c | 2 +-
mm/vmscan.c | 48 +++++++++++++++++++++++++++++++++++++++---------
3 files changed, 42 insertions(+), 11 deletions(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 39c24eb..25fe08d 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -645,6 +645,7 @@ typedef struct pglist_data {
wait_queue_head_t kswapd_wait;
struct task_struct *kswapd;
int kswapd_max_order;
+ enum zone_type high_zoneidx;
} pg_data_t;
#define node_present_pages(nid) (NODE_DATA(nid)->node_present_pages)
@@ -660,7 +661,7 @@ typedef struct pglist_data {
extern struct mutex zonelists_mutex;
void build_all_zonelists(void *data);
-void wakeup_kswapd(struct zone *zone, int order);
+void wakeup_kswapd(struct zone *zone, int order, enum zone_type high_zoneidx);
int zone_watermark_ok(struct zone *z, int order, unsigned long mark,
int classzone_idx, int alloc_flags);
enum memmap_context {
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 07a6544..344b597 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1921,7 +1921,7 @@ void wake_all_kswapd(unsigned int order, struct zonelist *zonelist,
struct zone *zone;
for_each_zone_zonelist(zone, z, zonelist, high_zoneidx)
- wakeup_kswapd(zone, order);
+ wakeup_kswapd(zone, order, high_zoneidx);
}
static inline int
diff --git a/mm/vmscan.c b/mm/vmscan.c
index d31d7ce..67e4283 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2165,11 +2165,14 @@ static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
* interoperates with the page allocator fallback scheme to ensure that aging
* of pages is balanced across the zones.
*/
-static unsigned long balance_pgdat(pg_data_t *pgdat, int order)
+static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
+ int high_zoneidx)
{
int all_zones_ok;
+ int any_zone_ok;
int priority;
int i;
+ int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
unsigned long total_scanned;
struct reclaim_state *reclaim_state = current->reclaim_state;
struct scan_control sc = {
@@ -2192,7 +2195,6 @@ loop_again:
count_vm_event(PAGEOUTRUN);
for (priority = DEF_PRIORITY; priority >= 0; priority--) {
- int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
unsigned long lru_pages = 0;
int has_under_min_watermark_zone = 0;
@@ -2201,6 +2203,7 @@ loop_again:
disable_swap_token();
all_zones_ok = 1;
+ any_zone_ok = 0;
/*
* Scan in the highmem->dma direction for the highest
@@ -2310,10 +2313,12 @@ loop_again:
* spectulatively avoid congestion waits
*/
zone_clear_flag(zone, ZONE_CONGESTED);
+ if (i <= high_zoneidx)
+ any_zone_ok = 1;
}
}
- if (all_zones_ok)
+ if (all_zones_ok || (order && any_zone_ok))
break; /* kswapd: all done */
/*
* OK, kswapd is getting into trouble. Take a nap, then take
@@ -2336,7 +2341,7 @@ loop_again:
break;
}
out:
- if (!all_zones_ok) {
+ if (!(all_zones_ok || (order && any_zone_ok))) {
cond_resched();
try_to_freeze();
@@ -2361,6 +2366,22 @@ out:
goto loop_again;
}
+ /* kswapd should always balance all zones for order-0 */
+ if (order && !all_zones_ok) {
+ order = sc.order = 0;
+ goto loop_again;
+ }
+
+ /*
+ * As kswapd could be going to sleep, unconditionally mark all
+ * zones as uncongested as kswapd is the only mechanism which
+ * clears congestion flags
+ */
+ for (i = 0; i <= end_zone; i++) {
+ struct zone *zone = pgdat->node_zones + i;
+ zone_clear_flag(zone, ZONE_CONGESTED);
+ }
+
return sc.nr_reclaimed;
}
@@ -2380,6 +2401,7 @@ out:
static int kswapd(void *p)
{
unsigned long order;
+ int zone_highidx;
pg_data_t *pgdat = (pg_data_t*)p;
struct task_struct *tsk = current;
DEFINE_WAIT(wait);
@@ -2410,19 +2432,24 @@ static int kswapd(void *p)
set_freezable();
order = 0;
+ zone_highidx = MAX_NR_ZONES;
for ( ; ; ) {
unsigned long new_order;
+ int new_zone_highidx;
int ret;
prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
new_order = pgdat->kswapd_max_order;
+ new_zone_highidx = pgdat->high_zoneidx;
pgdat->kswapd_max_order = 0;
- if (order < new_order) {
+ pgdat->high_zoneidx = MAX_NR_ZONES;
+ if (order < new_order || new_zone_highidx < zone_highidx) {
/*
* Don't sleep if someone wants a larger 'order'
- * allocation
+ * allocation or an order at a higher zone
*/
order = new_order;
+ zone_highidx = new_zone_highidx;
} else {
if (!freezing(current) && !kthread_should_stop()) {
long remaining = 0;
@@ -2451,6 +2478,7 @@ static int kswapd(void *p)
}
order = pgdat->kswapd_max_order;
+ zone_highidx = pgdat->high_zoneidx;
}
finish_wait(&pgdat->kswapd_wait, &wait);
@@ -2464,7 +2492,7 @@ static int kswapd(void *p)
*/
if (!ret) {
trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
- balance_pgdat(pgdat, order);
+ balance_pgdat(pgdat, order, zone_highidx);
}
}
return 0;
@@ -2473,7 +2501,7 @@ static int kswapd(void *p)
/*
* A zone is low on free memory, so wake its kswapd task to service it.
*/
-void wakeup_kswapd(struct zone *zone, int order)
+void wakeup_kswapd(struct zone *zone, int order, enum zone_type high_zoneidx)
{
pg_data_t *pgdat;
@@ -2483,8 +2511,10 @@ void wakeup_kswapd(struct zone *zone, int order)
pgdat = zone->zone_pgdat;
if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0, 0))
return;
- if (pgdat->kswapd_max_order < order)
+ if (pgdat->kswapd_max_order < order) {
pgdat->kswapd_max_order = order;
+ pgdat->high_zoneidx = min(pgdat->high_zoneidx, high_zoneidx);
+ }
trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
return;
--
1.7.1
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxxx For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>