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>

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 0bca2376bd42831ebb23b0f084dcbcb16e601d99..573d138fa7a592e5ff2637d1636ec0c87b00585e 100644 (file)
--- 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