linux-kernel - [PATCH v1 3/6] mm/page_isolation: drop WARN_ON_ONCE() in set_migratetype

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Date:   Tue, 30 Jun 2020 16:26:36 +0200
From:   David Hildenbrand <david@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     virtualization@...ts.linux-foundation.org, linux-mm@...ck.org,
        David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        "Michael S . Tsirkin" <mst@...hat.com>
Subject: [PATCH v1 3/6] 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 "movable_core". 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()).

Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Michael S. Tsirkin <mst@...hat.com>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
 mm/page_isolation.c | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index 553b49a34cf71..02a01bff6b219 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -58,16 +58,12 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
 	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;
 }
-- 
2.26.2