1 files changed, 45 insertions, 0 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index cefe6fe8d991..c54376a09f30 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1208,6 +1208,51 @@ void split_page(struct page *page, unsigned int order)
 }
 
 /*
+ * Similar to split_page except the page is already free. As this is only
+ * being used for migration, the migratetype of the block also changes.
+ * As this is called with interrupts disabled, the caller is responsible
+ * for calling arch_alloc_page() and kernel_map_page() after interrupts
+ * are enabled.
+ *
+ * Note: this is probably too low level an operation for use in drivers.
+ * Please consult with lkml before using this in your driver.
+ */
+int split_free_page(struct page *page)
+{
+        unsigned int order;
+        unsigned long watermark;
+        struct zone *zone;
+
+        BUG_ON(!PageBuddy(page));
+
+        zone = page_zone(page);
+        order = page_order(page);
+
+        /* Obey watermarks as if the page was being allocated */
+        watermark = low_wmark_pages(zone) + (1 << order);
+        if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
+                return 0;
+
+        /* Remove page from free list */
+        list_del(&page->lru);
+        zone->free_area[order].nr_free--;
+        rmv_page_order(page);
+        __mod_zone_page_state(zone, NR_FREE_PAGES, -(1UL << order));
+
+        /* Split into individual pages */
+        set_page_refcounted(page);
+        split_page(page, order);
+
+        if (order >= pageblock_order - 1) {
+                struct page *endpage = page + (1 << order) - 1;
+                for (; page < endpage; page += pageblock_nr_pages)
+                        set_pageblock_migratetype(page, MIGRATE_MOVABLE);
+        }
+
+        return 1 << order;
+}
+
+/*
  * Really, prep_compound_page() should be called from __rmqueue_bulk().  But
  * we cheat by calling it from here, in the order > 0 path.  Saves a branch
  * or two.