linux-kernel - [PATCH] mm/page_alloc: add zone to zonelist if populated

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Message-Id: <20220203020022.3044-1-richard.weiyang@gmail.com>
Date:   Thu,  3 Feb 2022 02:00:22 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     akpm@...ux-foundation.org, mhocko@...e.com,
        mgorman@...hsingularity.net
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Wei Yang <richard.weiyang@...il.com>,
        David Hildenbrand <david@...hat.com>
Subject: [PATCH] mm/page_alloc: add zone to zonelist if populated

During memory hotplug, when online/offline a zone, we need to rebuild
the zonelist for all nodes. Current behavior would lose a valid zone in
zonelist since only pick up managed_zone.

There are two cases for a zone with memory but still !managed.

  * all pages were allocated via memblock
  * all pages were taken by ballooning / virtio-mem

This state maybe temporary, since both of them may release some memory.
Then it end up with a managed zone not in zonelist.

This is introduced in 'commit 6aa303defb74 ("mm, vmscan: only allocate
and reclaim from zones with pages managed by the buddy allocator")'.
This patch restore the behavior.

Signed-off-by: Wei Yang <richard.weiyang@...il.com>
CC: Mel Gorman <mgorman@...hsingularity.net>
CC: David Hildenbrand <david@...hat.com>
Fixes: 6aa303defb74 ("mm, vmscan: only allocate and reclaim from zones with pages managed by the buddy allocator")
---
 mm/page_alloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index de15021a2887..b433a57ee76f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6092,7 +6092,7 @@ static int build_zonerefs_node(pg_data_t *pgdat, struct zoneref *zonerefs)
 	do {
 		zone_type--;
 		zone = pgdat->node_zones + zone_type;
-		if (managed_zone(zone)) {
+		if (populated_zone(zone)) {
 			zoneref_set_zone(zone, &zonerefs[nr_zones++]);
 			check_highest_zone(zone_type);
 		}
-- 
2.33.1