[RFC PATCH v3 30/35] mm: Provide a mechanism to check if a given page is in the region allocator

[Srivatsa S. Bhat]

With the introduction of the region allocator, a freepage can be either
in one of the buddy freelists or in the region allocator. In cases where we
want to move freepages to a given migratetype's freelists, we will need to
know where they were originally located. So provide a helper to distinguish
whether the freepage resides in the region allocator or the buddy freelists.

Signed-off-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com>
---

 mm/page_alloc.c |   31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a62730b..3f49ca8 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1047,6 +1047,37 @@ static int del_from_region_allocator(struct zone *zone, 
unsigned int order,
 }
 
 /*
+ * Return 1 if the page is in the region allocator, else return 0
+ * (which usually means that the page is in the buddy freelists).
+ */
+static int page_in_region_allocator(struct page *page)
+{
+       struct region_allocator *reg_alloc;
+       struct free_area_region *reg_area;
+       int order, region_id;
+
+       /* We keep only MAX_ORDER-1 pages in the region allocator */
+       order = page_order(page);
+       if (order != MAX_ORDER-1)
+               return 0;
+
+       /*
+        * It is sufficient to check if (any of) the pages belonging to
+        * that region are in the region allocator, because a page resides
+        * in the region allocator if and only if all the pages of that
+        * region are also in the region allocator.
+        */
+       region_id = page_zone_region_id(page);
+       reg_alloc = &page_zone(page)->region_allocator;
+       reg_area = &reg_alloc->region[region_id].region_area[order];
+
+       if (reg_area->nr_free)
+               return 1;
+
+       return 0;
+}
+
+/*
  * Freeing function for a buddy system allocator.
  *
  * The concept of a buddy system is to maintain direct-mapped table

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