[PATCH next] mm/vmscan: __isolate_lru_page_prepare clean up

[Alex Shi]

The function just return 2 results, so use a 'switch' to deal with its
result is unnecessary, and simplify it to a bool func as Vlastimil
suggested.

Also removed 'goto' in using by reusing list_move().

Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 mm/compaction.c |  2 +-
 mm/vmscan.c     | 53 ++++++++++++++++++++++++-------------------------
 2 files changed, 27 insertions(+), 28 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index b68931854253..8d71ffebe6cb 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -988,7 +988,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 		if (unlikely(!get_page_unless_zero(page)))
 			goto isolate_fail;
 
-		if (__isolate_lru_page_prepare(page, isolate_mode) != 0)
+		if (!__isolate_lru_page_prepare(page, isolate_mode))
 			goto isolate_fail_put;
 
 		/* Try isolate the page */
diff --git a/mm/vmscan.c b/mm/vmscan.c
index c6f94e55c3fe..7f32c1979804 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1540,7 +1540,7 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone,
  */
 int __isolate_lru_page_prepare(struct page *page, isolate_mode_t mode)
 {
-	int ret = -EBUSY;
+	int ret = false;
 
 	/* Only take pages on the LRU. */
 	if (!PageLRU(page))
@@ -1590,7 +1590,7 @@ int __isolate_lru_page_prepare(struct page *page, isolate_mode_t mode)
 	if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
 		return ret;
 
-	return 0;
+	return true;
 }
 
 /*
@@ -1674,35 +1674,34 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 		 * only when the page is being freed somewhere else.
 		 */
 		scan += nr_pages;
-		switch (__isolate_lru_page_prepare(page, mode)) {
-		case 0:
+		if (!__isolate_lru_page_prepare(page, mode)) {
+			/* else it is being freed elsewhere */
+			list_move(&page->lru, src);
+			continue;
+		}
+		/*
+		 * Be careful not to clear PageLRU until after we're
+		 * sure the page is not being freed elsewhere -- the
+		 * page release code relies on it.
+		 */
+		if (unlikely(!get_page_unless_zero(page))) {
+			list_move(&page->lru, src);
+			continue;
+		}
+
+		if (!TestClearPageLRU(page)) {
 			/*
-			 * Be careful not to clear PageLRU until after we're
-			 * sure the page is not being freed elsewhere -- the
-			 * page release code relies on it.
+			 * This page may in other isolation path,
+			 * but we still hold lru_lock.
 			 */
-			if (unlikely(!get_page_unless_zero(page)))
-				goto busy;
-
-			if (!TestClearPageLRU(page)) {
-				/*
-				 * This page may in other isolation path,
-				 * but we still hold lru_lock.
-				 */
-				put_page(page);
-				goto busy;
-			}
-
-			nr_taken += nr_pages;
-			nr_zone_taken[page_zonenum(page)] += nr_pages;
-			list_move(&page->lru, dst);
-			break;
-
-		default:
-busy:
-			/* else it is being freed elsewhere */
+			put_page(page);
 			list_move(&page->lru, src);
+			continue;
 		}
+
+		nr_taken += nr_pages;
+		nr_zone_taken[page_zonenum(page)] += nr_pages;
+		list_move(&page->lru, dst);
 	}
 
 	/*
-- 
2.29.GIT