mm/page_alloc: refactor out __alloc_contig_migrate_alloc()

__alloc_contig_migrate_alloc() can be used by memory-hotplug so refactor
it out (move + rename as a common name) into page_isolation.c.

[akpm@linux-foundation.org: checkpatch fixes]
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Wen Congyang <wency@cn.fujitsu.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/page-isolation.h

@@ -41,6 +41,7 @@ int test_pages_isolated(unsigned long start_pfn, unsigned long end_pfn);
  */
 int set_migratetype_isolate(struct page *page);
 void unset_migratetype_isolate(struct page *page, unsigned migratetype);
-
+struct page *alloc_migrate_target(struct page *page, unsigned long private,
+				int **resultp);
 
 #endif

mm/page_alloc.c

@@ -5667,18 +5667,6 @@ static unsigned long pfn_max_align_up(unsigned long pfn)
 				pageblock_nr_pages));
 }
 
-static struct page *
-__alloc_contig_migrate_alloc(struct page *page, unsigned long private,
-			     int **resultp)
-{
-	gfp_t gfp_mask = GFP_USER | __GFP_MOVABLE;
-
-	if (PageHighMem(page))
-		gfp_mask |= __GFP_HIGHMEM;
-
-	return alloc_page(gfp_mask);
-}
-
 /* [start, end) must belong to a single zone. */
 static int __alloc_contig_migrate_range(struct compact_control *cc,
 					unsigned long start, unsigned long end)
@@ -5714,7 +5702,7 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
 		reclaim_clean_pages_from_list(cc->zone, &cc->migratepages);
 
 		ret = migrate_pages(&cc->migratepages,
-				    __alloc_contig_migrate_alloc,
+				    alloc_migrate_target,
 				    0, false, MIGRATE_SYNC);
 	}
 

mm/page_isolation.c

@@ -255,3 +255,14 @@ int test_pages_isolated(unsigned long start_pfn, unsigned long end_pfn)
 	spin_unlock_irqrestore(&zone->lock, flags);
 	return ret ? 0 : -EBUSY;
 }
+
+struct page *alloc_migrate_target(struct page *page, unsigned long private,
+				  int **resultp)
+{
+	gfp_t gfp_mask = GFP_USER | __GFP_MOVABLE;
+
+	if (PageHighMem(page))
+		gfp_mask |= __GFP_HIGHMEM;
+
+	return alloc_page(gfp_mask);
+}