thp: use compaction in kswapd for GFP_ATOMIC order > 0

This takes advantage of memory compaction to properly generate pages of
order > 0 if regular page reclaim fails and priority level becomes more
severe and we don't reach the proper watermarks.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 20 insertions, 10 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index cfdef0bcc7ab..f5b762ae23a2 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -41,6 +41,7 @@
 #include <linux/memcontrol.h>
 #include <linux/delayacct.h>
 #include <linux/sysctl.h>
+#include <linux/compaction.h>
 
 #include <asm/tlbflush.h>
 #include <asm/div64.h>
@@ -2382,6 +2383,7 @@ loop_again:
                  * cause too much scanning of the lower zones.
                  */
                 for (i = 0; i <= end_zone; i++) {
+                        int compaction;
                         struct zone *zone = pgdat->node_zones + i;
                         int nr_slab;
 
@@ -2411,9 +2413,26 @@ loop_again:
                                                 lru_pages);
                         sc.nr_reclaimed += reclaim_state->reclaimed_slab;
                         total_scanned += sc.nr_scanned;
+
+                        compaction = 0;
+                        if (order &&
+                            zone_watermark_ok(zone, 0,
+                                               high_wmark_pages(zone),
+                                              end_zone, 0) &&
+                            !zone_watermark_ok(zone, order,
+                                               high_wmark_pages(zone),
+                                               end_zone, 0)) {
+                                compact_zone_order(zone,
+                                                   order,
+                                                   sc.gfp_mask, false,
+                                                   COMPACT_MODE_KSWAPD);
+                                compaction = 1;
+                        }
+
                         if (zone->all_unreclaimable)
                                 continue;
-                        if (nr_slab == 0 && !zone_reclaimable(zone))
+                        if (!compaction && nr_slab == 0 &&
+                            !zone_reclaimable(zone))
                                 zone->all_unreclaimable = 1;
                         /*
                          * If we've done a decent amount of scanning and
@@ -2424,15 +2443,6 @@ loop_again:
                             total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
                                 sc.may_writepage = 1;
 
-                        /*
-                         * Compact the zone for higher orders to reduce
-                         * latencies for higher-order allocations that
-                         * would ordinarily call try_to_compact_pages()
-                         */
-                        if (sc.order > PAGE_ALLOC_COSTLY_ORDER)
-                                compact_zone_order(zone, sc.order, sc.gfp_mask,
-                                                        false);
-
                         if (!zone_watermark_ok_safe(zone, order,
                                         high_wmark_pages(zone), end_zone, 0)) {
                                 all_zones_ok = 0;