linux-kernel - [PATCH] Revert "mm/vmstat.c: do not show lowmem reserve protection information of empty zone"

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Message-Id: <20200811075412.12872-1-bhe@redhat.com>
Date:   Tue, 11 Aug 2020 15:54:12 +0800
From:   Baoquan He <bhe@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        sonnyrao@...omium.org, yuzhao@...gle.com, rientjes@...gle.com,
        bhe@...hat.com
Subject: [PATCH] Revert "mm/vmstat.c: do not show lowmem reserve protection information of empty zone"

This reverts commit 26e7deadaae1755faf1f6d1a68988c4b8348df59.

Sonny reported that one of their tests started failing on the latest
kernel on their Chrome OS platform. The root cause is that the above
commit removed the protection line of empty zone, while the parser used
in the test relies on the protection line to mark the end of each zone.

Let's revert it to avoid breaking userspace testing or applications.

Cc: <stable@...r.kernel.org> # 5.8.x
Reported-by: Sonny Rao <sonnyrao@...omium.org>
Signed-off-by: Baoquan He <bhe@...hat.com>
---
 mm/vmstat.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 5b35c0eb8c57..62376dc66ec0 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1644,12 +1644,6 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
 		   zone->present_pages,
 		   zone_managed_pages(zone));
 
-	/* If unpopulated, no other information is useful */
-	if (!populated_zone(zone)) {
-		seq_putc(m, '\n');
-		return;
-	}
-
 	seq_printf(m,
 		   "\n        protection: (%ld",
 		   zone->lowmem_reserve[0]);
@@ -1657,6 +1651,12 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
 		seq_printf(m, ", %ld", zone->lowmem_reserve[i]);
 	seq_putc(m, ')');
 
+	/* If unpopulated, no other information is useful */
+	if (!populated_zone(zone)) {
+		seq_putc(m, '\n');
+		return;
+	}
+
 	for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
 		seq_printf(m, "\n      %-12s %lu", zone_stat_name(i),
 			   zone_page_state(zone, i));
-- 
2.17.2