[RFC 2/4] mm: make shrink_page_list with pages from multiple zones

[Minchan Kim <minchan@kernel.org>]

Now shrink_page_list expects all pages come from a same zone
but it's too limited to use it.

This patch removes the dependency so next patch can use
shrink_page_list with pages from multiple zones.

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 mm/vmscan.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index d3dc95f..9434ba2 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -705,7 +705,8 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 			goto keep;
 
 		VM_BUG_ON(PageActive(page));
-		VM_BUG_ON(page_zone(page) != zone);
+		if (zone)
+			VM_BUG_ON(page_zone(page) != zone);
 
 		sc->nr_scanned++;
 
@@ -951,7 +952,7 @@ keep:
 	 * back off and wait for congestion to clear because further reclaim
 	 * will encounter the same problem
 	 */
-	if (nr_dirty && nr_dirty == nr_congested && global_reclaim(sc))
+	if (nr_dirty && nr_dirty == nr_congested && global_reclaim(sc) && zone)
 		zone_set_flag(zone, ZONE_CONGESTED);
 
 	free_hot_cold_page_list(&free_pages, 1);
-- 
1.8.2

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