vmscan: stop kswapd waiting on congestion when the min watermark is not being met

If reclaim fails to make sufficient progress, the priority is raised.
Once the priority is higher, kswapd starts waiting on congestion.
However, if the zone is below the min watermark then kswapd needs to
continue working without delay as there is a danger of an increased rate
of GFP_ATOMIC allocation failure.

This patch changes the conditions under which kswapd waits on congestion
by only going to sleep if the min watermarks are being met.

[mel@csn.ul.ie: add stats to track how relevant the logic is]
[mel@csn.ul.ie: make kswapd only check its own zones and rename the relevant counters]
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index fd5be240c0b72f075d135d2bc0e00c7d7dd9aca8..ee03bba9c5df8e9d0b0586fcfff5ef39e254c717 100644 (file)
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -40,7 +40,8 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
                PGSCAN_ZONE_RECLAIM_FAILED,
 #endif
                PGINODESTEAL, SLABS_SCANNED, KSWAPD_STEAL, KSWAPD_INODESTEAL,
-               KSWAPD_PREMATURE_FAST, KSWAPD_PREMATURE_SLOW,
+               KSWAPD_LOW_WMARK_HIT_QUICKLY, KSWAPD_HIGH_WMARK_HIT_QUICKLY,
+               KSWAPD_SKIP_CONGESTION_WAIT,
                PAGEOUTRUN, ALLOCSTALL, PGROTATED,
 #ifdef CONFIG_HUGETLB_PAGE
                HTLB_BUDDY_PGALLOC, HTLB_BUDDY_PGALLOC_FAIL,

diff --git a/mm/vmscan.c b/mm/vmscan.c
index e176bd3936dad2a353e1747de62d128e79f0587b..cb69f717799f65e4deb33ccca56d78ba89c53f6f 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1905,19 +1905,25 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
 #endif
 
 /* is kswapd sleeping prematurely? */
-static int sleeping_prematurely(int order, long remaining)
+static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
 {
-       struct zone *zone;
+       int i;
 
        /* If a direct reclaimer woke kswapd within HZ/10, it's premature */
        if (remaining)
                return 1;
 
        /* If after HZ/10, a zone is below the high mark, it's premature */
-       for_each_populated_zone(zone)
+       for (i = 0; i < pgdat->nr_zones; i++) {
+               struct zone *zone = pgdat->node_zones + i;
+
+               if (!populated_zone(zone))
+                       continue;
+
                if (!zone_watermark_ok(zone, order, high_wmark_pages(zone),
                                                                0, 0))
                        return 1;
+       }
 
        return 0;
 }
@@ -1979,6 +1985,7 @@ loop_again:
        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;
 
                /* The swap token gets in the way of swapout... */
                if (!priority)
@@ -2085,6 +2092,15 @@ loop_again:
                        if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
                            total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
                                sc.may_writepage = 1;
+
+                       /*
+                        * We are still under min water mark. it mean we have
+                        * GFP_ATOMIC allocation failure risk. Hurry up!
+                        */
+                       if (!zone_watermark_ok(zone, order, min_wmark_pages(zone),
+                                             end_zone, 0))
+                               has_under_min_watermark_zone = 1;
+
                }
                if (all_zones_ok)
                        break;          /* kswapd: all done */
@@ -2092,8 +2108,12 @@ loop_again:
                 * OK, kswapd is getting into trouble.  Take a nap, then take
                 * another pass across the zones.
                 */
-               if (total_scanned && priority < DEF_PRIORITY - 2)
-                       congestion_wait(BLK_RW_ASYNC, HZ/10);
+               if (total_scanned && (priority < DEF_PRIORITY - 2)) {
+                       if (has_under_min_watermark_zone)
+                               count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
+                       else
+                               congestion_wait(BLK_RW_ASYNC, HZ/10);
+               }
 
                /*
                 * We do this so kswapd doesn't build up large priorities for
@@ -2207,7 +2227,7 @@ static int kswapd(void *p)
                                long remaining = 0;
 
                                /* Try to sleep for a short interval */
-                               if (!sleeping_prematurely(order, remaining)) {
+                               if (!sleeping_prematurely(pgdat, order, remaining)) {
                                        remaining = schedule_timeout(HZ/10);
                                        finish_wait(&pgdat->kswapd_wait, &wait);
                                        prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
@@ -2218,13 +2238,13 @@ static int kswapd(void *p)
                                 * premature sleep. If not, then go fully
                                 * to sleep until explicitly woken up
                                 */
-                               if (!sleeping_prematurely(order, remaining))
+                               if (!sleeping_prematurely(pgdat, order, remaining))
                                        schedule();
                                else {
                                        if (remaining)
-                                               count_vm_event(KSWAPD_PREMATURE_FAST);
+                                               count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
                                        else
-                                               count_vm_event(KSWAPD_PREMATURE_SLOW);
+                                               count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
                                }
                        }
 

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 63ab71455c5bcd1e6ca46b77ee9c939654ae3fcd..6051fbab67ba26533594103c62790f779cd21c08 100644 (file)
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -683,8 +683,9 @@ static const char * const vmstat_text[] = {
        "slabs_scanned",
        "kswapd_steal",
        "kswapd_inodesteal",
-       "kswapd_slept_prematurely_fast",
-       "kswapd_slept_prematurely_slow",
+       "kswapd_low_wmark_hit_quickly",
+       "kswapd_high_wmark_hit_quickly",
+       "kswapd_skip_congestion_wait",
        "pageoutrun",
        "allocstall",