mm: don't wait on congested zones in balance_pgdat()

From: Zlatko Calusic <zlatko.calusic@iskon.hr>

Commit 92df3a723f84 ("mm: vmscan: throttle reclaim if encountering too
many dirty pages under writeback") introduced waiting on congested zones
based on a sane algorithm in shrink_inactive_list().

What this means is that there's no more need for throttling and
additional heuristics in balance_pgdat().  So, let's remove it and tidy
up the code.

Signed-off-by: Zlatko Calusic <zlatko.calusic@iskon.hr>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Johannes Weiner <jweiner@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 1 insertions, 29 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 8fde2fc223d9..b93968b71dc6 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2617,7 +2617,6 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
                                                         int *classzone_idx)
 {
         bool pgdat_is_balanced = false;
-        struct zone *unbalanced_zone;
         int i;
         int end_zone = 0;       /* Inclusive.  0 = ZONE_DMA */
         unsigned long total_scanned;
@@ -2648,9 +2647,6 @@ loop_again:
 
         do {
                 unsigned long lru_pages = 0;
-                int has_under_min_watermark_zone = 0;
-
-                unbalanced_zone = NULL;
 
                 /*
                  * Scan in the highmem->dma direction for the highest
@@ -2790,17 +2786,7 @@ loop_again:
                                 continue;
                         }
 
-                        if (!zone_balanced(zone, testorder, 0, end_zone)) {
-                                unbalanced_zone = zone;
-                                /*
-                                 * We are still under min water mark.  This
-                                 * means that we have a GFP_ATOMIC allocation
-                                 * failure risk. Hurry up!
-                                 */
-                                if (!zone_watermark_ok_safe(zone, order,
-                                            min_wmark_pages(zone), end_zone, 0))
-                                        has_under_min_watermark_zone = 1;
-                        } else {
+                        if (zone_balanced(zone, testorder, 0, end_zone))
                                 /*
                                  * If a zone reaches its high watermark,
                                  * consider it to be no longer congested. It's
@@ -2809,8 +2795,6 @@ loop_again:
                                  * speculatively avoid congestion waits
                                  */
                                 zone_clear_flag(zone, ZONE_CONGESTED);
-                        }
-
                 }
 
                 /*
@@ -2828,17 +2812,6 @@ loop_again:
                 }
 
                 /*
-                 * OK, kswapd is getting into trouble.  Take a nap, then take
-                 * another pass across the zones.
-                 */
-                if (total_scanned && (sc.priority < DEF_PRIORITY - 2)) {
-                        if (has_under_min_watermark_zone)
-                                count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
-                        else if (unbalanced_zone)
-                                wait_iff_congested(unbalanced_zone, BLK_RW_ASYNC, HZ/10);
-                }
-
-                /*
                  * We do this so kswapd doesn't build up large priorities for
                  * example when it is freeing in parallel with allocators. It
                  * matches the direct reclaim path behaviour in terms of impact
diff --git a/mm/vmstat.c b/mm/vmstat.c
index c9d1f68120cd..57f02fd1768b 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -770,7 +770,6 @@ const char * const vmstat_text[] = {
         "kswapd_inodesteal",
         "kswapd_low_wmark_hit_quickly",
         "kswapd_high_wmark_hit_quickly",
-        "kswapd_skip_congestion_wait",
         "pageoutrun",
         "allocstall",