mm, page_alloc: fix dirtyable highmem calculation

When I tested vmscale in mmtest in 32bit, I found the benchmark was slow
down 0.5 times.

                base        node
                   1    global-1
User           12.98       16.04
System        147.61      166.42
Elapsed        26.48       38.08

With vmstat, I found IO wait avg is much increased compared to base.

The reason was highmem_dirtyable_memory accumulates free pages and
highmem_file_pages from HIGHMEM to MOVABLE zones which was wrong.  With
that, dirth_thresh in throtlle_vm_write is always 0 so that it calls
congestion_wait frequently if writeback starts.

With this patch, it is much recovered.

                base        node          fi
                   1    global-1         fix
User           12.98       16.04       13.78
System        147.61      166.42      143.92
Elapsed        26.48       38.08       29.64

Link: http://lkml.kernel.org/r/1468404004-5085-4-git-send-email-mgorman@techsingularity.net
Signed-off-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 6 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 0bca2376bd42..573d138fa7a5 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -307,27 +307,31 @@ static unsigned long highmem_dirtyable_memory(unsigned long total)
 {
 #ifdef CONFIG_HIGHMEM
         int node;
-        unsigned long x = 0;
+        unsigned long x;
         int i;
-        unsigned long dirtyable = atomic_read(&highmem_file_pages);
+        unsigned long dirtyable = 0;
 
         for_each_node_state(node, N_HIGH_MEMORY) {
                 for (i = ZONE_NORMAL + 1; i < MAX_NR_ZONES; i++) {
                         struct zone *z;
+                        unsigned long nr_pages;
 
                         if (!is_highmem_idx(i))
                                 continue;
 
                         z = &NODE_DATA(node)->node_zones[i];
-                        dirtyable += zone_page_state(z, NR_FREE_PAGES);
+                        if (!populated_zone(z))
+                                continue;
 
+                        nr_pages = zone_page_state(z, NR_FREE_PAGES);
                         /* watch for underflows */
-                        dirtyable -= min(dirtyable, high_wmark_pages(z));
-
-                        x += dirtyable;
+                        nr_pages -= min(nr_pages, high_wmark_pages(z));
+                        dirtyable += nr_pages;
                 }
         }
 
+        x = dirtyable + atomic_read(&highmem_file_pages);
+
         /*
          * Unreclaimable memory (kernel memory or anonymous memory
          * without swap) can bring down the dirtyable pages below