mm: clean up __count_immobile_pages()

The __count_immobile_pages() naming is rather awkward.  Choose a more
clear name and add a comment.

Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@suse.cz>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 18 insertions, 16 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index bb790f5919e3..fba2a1223f14 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5471,26 +5471,28 @@ void set_pageblock_flags_group(struct page *page, unsigned long flags,
 }
 
 /*
- * This is designed as sub function...plz see page_isolation.c also.
- * set/clear page block's type to be ISOLATE.
- * page allocater never alloc memory from ISOLATE block.
+ * This function checks whether pageblock includes unmovable pages or not.
+ * If @count is not zero, it is okay to include less @count unmovable pages
+ *
+ * PageLRU check wihtout isolation or lru_lock could race so that
+ * MIGRATE_MOVABLE block might include unmovable pages. It means you can't
+ * expect this function should be exact.
  */
-
-static int
-__count_immobile_pages(struct zone *zone, struct page *page, int count)
+static bool
+__has_unmovable_pages(struct zone *zone, struct page *page, int count)
 {
         unsigned long pfn, iter, found;
         int mt;
 
         /*
          * For avoiding noise data, lru_add_drain_all() should be called
-         * If ZONE_MOVABLE, the zone never contains immobile pages
+         * If ZONE_MOVABLE, the zone never contains unmovable pages
          */
         if (zone_idx(zone) == ZONE_MOVABLE)
-                return true;
+                return false;
         mt = get_pageblock_migratetype(page);
         if (mt == MIGRATE_MOVABLE || is_migrate_cma(mt))
-                return true;
+                return false;
 
         pfn = page_to_pfn(page);
         for (found = 0, iter = 0; iter < pageblock_nr_pages; iter++) {
@@ -5528,9 +5530,9 @@ __count_immobile_pages(struct zone *zone, struct page *page, int count)
                  * page at boot.
                  */
                 if (found > count)
-                        return false;
+                        return true;
         }
-        return true;
+        return false;
 }
 
 bool is_pageblock_removable_nolock(struct page *page)
@@ -5554,7 +5556,7 @@ bool is_pageblock_removable_nolock(struct page *page)
                         zone->zone_start_pfn + zone->spanned_pages <= pfn)
                 return false;
 
-        return __count_immobile_pages(zone, page, 0);
+        return !__has_unmovable_pages(zone, page, 0);
 }
 
 int set_migratetype_isolate(struct page *page)
@@ -5593,12 +5595,12 @@ int set_migratetype_isolate(struct page *page)
          * FIXME: Now, memory hotplug doesn't call shrink_slab() by itself.
          * We just check MOVABLE pages.
          */
-        if (__count_immobile_pages(zone, page, arg.pages_found))
+        if (!__has_unmovable_pages(zone, page, arg.pages_found))
                 ret = 0;
-
         /*
-         * immobile means "not-on-lru" paes. If immobile is larger than
-         * removable-by-driver pages reported by notifier, we'll fail.
+         * Unmovable means "not-on-lru" pages. If Unmovable pages are
+         * larger than removable-by-driver pages reported by notifier,
+         * we'll fail.
          */
 
 out: