linux-kernel - [PATCH] mm, vmscan: prevent kswapd sleeping prematurely due to mismatched classzone

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Message-ID: <20170406174538.5msrznj6nt6qpbx5@suse.de>
Date:   Thu, 6 Apr 2017 18:45:38 +0100
From:   Mel Gorman <mgorman@...e.de>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Michal Hocko <mhocko@...nel.org>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: [PATCH] mm, vmscan: prevent kswapd sleeping prematurely due to
 mismatched classzone_idx -fix

The patch "mm, vmscan: prevent kswapd sleeping prematurely due to mismatched
classzone_idx" has different initial starting conditions when kswapd
is asleep. kswapd initialises it properly when it starts but the patch
initialises kswapd_classzone_idx early and trips on a warning in
free_area_init_node. This patch leaves the kswapd_classzone_idx as zero
and defers to kswapd to initialise it properly when it starts.

This is a fix to the mmotm patch
mm-vmscan-prevent-kswapd-sleeping-prematurely-due-to-mismatched-classzone_idx.patch

Signed-off-by: Mel Gorman <mgorman@...e.de>
Acked-by: Michal Hocko <mhocko@...e.com>
---
 mm/memory_hotplug.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 2309a7fbec93..76d4745513ee 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1214,10 +1214,14 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
 
 		arch_refresh_nodedata(nid, pgdat);
 	} else {
-		/* Reset the nr_zones, order and classzone_idx before reuse */
+		/*
+		 * Reset the nr_zones, order and classzone_idx before reuse.
+		 * Note that kswapd will init kswapd_classzone_idx properly
+		 * when it starts in the near future.
+		 */
 		pgdat->nr_zones = 0;
 		pgdat->kswapd_order = 0;
-		pgdat->kswapd_classzone_idx = MAX_NR_ZONES;
+		pgdat->kswapd_classzone_idx = 0;
 	}
 
 	/* we can use NODE_DATA(nid) from here */