[patch 127/181] mm/page_isolation: drop WARN_ON_ONCE() in set_migratetype_isolate()

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From: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm/page_isolation: drop WARN_ON_ONCE() in set_migratetype_isolate()

Inside has_unmovable_pages(), we have a comment describing how unmovable
data could end up in ZONE_MOVABLE - via "movablecore".  Also, besides
checking if the first page in the pageblock is reserved, we don't perform
any further checks in case of ZONE_MOVABLE.

In case of memory offlining, we set REPORT_FAILURE, properly dump_page()
the page and handle the error gracefully.  alloc_contig_pages() users
currently never allocate from ZONE_MOVABLE.  E.g., hugetlb uses
alloc_contig_pages() for the allocation of gigantic pages only, which will
never end up on the MOVABLE zone (see htlb_alloc_mask()).

Link: http://lkml.kernel.org/r/20200816125333.7434-4-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: Baoquan He <bhe@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Pankaj Gupta <pankaj.gupta.linux@xxxxxxxxx>
Cc: Jason Wang <jasowang@xxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxx>
Cc: Qian Cai <cai@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/page_isolation.c |   15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

--- a/mm/page_isolation.c~mm-page_isolation-drop-warn_on_once-in-set_migratetype_isolate
+++ a/mm/page_isolation.c
@@ -57,15 +57,12 @@ static int set_migratetype_isolate(struc
 	spin_unlock_irqrestore(&zone->lock, flags);
 	if (!ret) {
 		drain_all_pages(zone);
-	} else {
-		WARN_ON_ONCE(zone_idx(zone) == ZONE_MOVABLE);
-
-		if ((isol_flags & REPORT_FAILURE) && unmovable)
-			/*
-			 * printk() with zone->lock held will likely trigger a
-			 * lockdep splat, so defer it here.
-			 */
-			dump_page(unmovable, "unmovable page");
+	} else if ((isol_flags & REPORT_FAILURE) && unmovable) {
+		/*
+		 * printk() with zone->lock held will likely trigger a
+		 * lockdep splat, so defer it here.
+		 */
+		dump_page(unmovable, "unmovable page");
 	}
 
 	return ret;
_




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