mm: reduce the amount of work done when updating min_free_kbytes

Orabug: 14073214
When min_free_kbytes is updated, some pageblocks are marked
MIGRATE_RESERVE.  Ordinarily, this work is unnoticable as it happens early
in boot but on large machines with 1TB of memory, this has been reported
to delay boot times, probably due to the NUMA distances involved.

The bulk of the work is due to calling calling pageblock_is_reserved() an
unnecessary amount of times and accessing far more struct page metadata
than is necessary.  This patch significantly reduces the amount of work
done by setup_zone_migrate_reserve() improving boot times on 1TB machines.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit 938929f14cb595f43cd1a4e63e22d36cab1e4a1f)

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8439d2a04f2dd4a65223ce2c8b4a83a6ecac0416..9394c5e36ff80fc4a2e5a429510c644579a8e130 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3418,25 +3418,33 @@ static void setup_zone_migrate_reserve(struct zone *zone)
                if (page_to_nid(page) != zone_to_nid(zone))
                        continue;
 
-               /* Blocks with reserved pages will never free, skip them. */
-               block_end_pfn = min(pfn + pageblock_nr_pages, end_pfn);
-               if (pageblock_is_reserved(pfn, block_end_pfn))
-                       continue;
-
                block_migratetype = get_pageblock_migratetype(page);
 
-               /* If this block is reserved, account for it */
-               if (reserve > 0 && block_migratetype == MIGRATE_RESERVE) {
-                       reserve--;
-                       continue;
-               }
+               /* Only test what is necessary when the reserves are not met */
+               if (reserve > 0) {
+                       /*
+                        * Blocks with reserved pages will never free, skip
+                        * them.
+                        */
+                       block_end_pfn = min(pfn + pageblock_nr_pages, end_pfn);
+                       if (pageblock_is_reserved(pfn, block_end_pfn))
+                               continue;
 
-               /* Suitable for reserving if this block is movable */
-               if (reserve > 0 && block_migratetype == MIGRATE_MOVABLE) {
-                       set_pageblock_migratetype(page, MIGRATE_RESERVE);
-                       move_freepages_block(zone, page, MIGRATE_RESERVE);
-                       reserve--;
-                       continue;
+                       /* If this block is reserved, account for it */
+                       if (block_migratetype == MIGRATE_RESERVE) {
+                               reserve--;
+                               continue;
+                       }
+
+                       /* Suitable for reserving if this block is movable */
+                       if (block_migratetype == MIGRATE_MOVABLE) {
+                               set_pageblock_migratetype(page,
+                                                       MIGRATE_RESERVE);
+                               move_freepages_block(zone, page,
+                                                       MIGRATE_RESERVE);
+                               reserve--;
+                               continue;
+                       }
                }
 
                /*