zsmalloc: cosmetic compaction code adjustments

Change zs_object_copy() argument order to be (DST, SRC) rather than
(SRC, DST).  copy/move functions usually have (to, from) arguments
order.

Rename alloc_target_page() to isolate_target_page().  This function
doesn't allocate anything, it isolates target page, pretty much like
isolate_source_page().

Tweak __zs_compact() comment.
Signed-off-by: NSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: NMinchan Kim <minchan@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/zsmalloc.c

@@ -1471,7 +1471,7 @@ void zs_free(struct zs_pool *pool, unsigned long handle)
 }
 EXPORT_SYMBOL_GPL(zs_free);
 
-static void zs_object_copy(unsigned long src, unsigned long dst,
+static void zs_object_copy(unsigned long dst, unsigned long src,
 				struct size_class *class)
 {
 	struct page *s_page, *d_page;
@@ -1612,7 +1612,7 @@ static int migrate_zspage(struct zs_pool *pool, struct size_class *class,
 
 		used_obj = handle_to_obj(handle);
 		free_obj = obj_malloc(d_page, class, handle);
-		zs_object_copy(used_obj, free_obj, class);
+		zs_object_copy(free_obj, used_obj, class);
 		index++;
 		record_obj(handle, free_obj);
 		unpin_tag(handle);
@@ -1628,7 +1628,7 @@ static int migrate_zspage(struct zs_pool *pool, struct size_class *class,
 	return ret;
 }
 
-static struct page *alloc_target_page(struct size_class *class)
+static struct page *isolate_target_page(struct size_class *class)
 {
 	int i;
 	struct page *page;
@@ -1718,11 +1718,11 @@ static unsigned long __zs_compact(struct zs_pool *pool,
 		cc.index = 0;
 		cc.s_page = src_page;
 
-		while ((dst_page = alloc_target_page(class))) {
+		while ((dst_page = isolate_target_page(class))) {
 			cc.d_page = dst_page;
 			/*
-			 * If there is no more space in dst_page, try to
-			 * allocate another zspage.
+			 * If there is no more space in dst_page, resched
+			 * and see if anyone had allocated another zspage.
 			 */
 			if (!migrate_zspage(pool, class, &cc))
 				break;