linux-kernel - [RFC 01/10] autonuma: Fix watermark checking in migrate_balanced

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Date:   Fri,  1 Nov 2019 15:57:18 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Huang Ying <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>, Rik van Riel <riel@...hat.com>,
        Mel Gorman <mgorman@...e.de>, Ingo Molnar <mingo@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Fengguang Wu <fengguang.wu@...el.com>
Subject: [RFC 01/10] autonuma: Fix watermark checking in migrate_balanced_pgdat()

From: Huang Ying <ying.huang@...el.com>

When zone_watermark_ok() is called in migrate_balanced_pgdat() to
check migration target node, the parameter classzone_idx (for
requested zone) is specified as 0 (ZONE_DMA).  But when allocating
memory for autonuma in alloc_misplaced_dst_page(), the requested zone
from GFP flags is ZONE_MOVABLE.  That is, the requested zone is
different.  The size of lowmem_reserve for the different requested
zone is different.  And this may cause some issues.

For example, in the zoneinfo of a test machine as below,

Node 0, zone    DMA32
  pages free     61592
        min      29
        low      454
        high     879
        spanned  1044480
        present  442306
        managed  425921
        protection: (0, 0, 62457, 62457, 62457)

The free page number of ZONE_DMA32 is greater than "high watermark +
lowmem_reserve[ZONE_DMA]", but less than "high watermark +
lowmem_reserve[ZONE_MOVABLE]".  And because __alloc_pages_node() in
alloc_misplaced_dst_page() requests ZONE_MOVABLE, the
zone_watermark_ok() on ZONE_DMA32 in migrate_balanced_pgdat() may
always return true.  So, autonuma may not stop even when memory
pressure in node 0 is heavy.

To fix the issue, ZONE_MOVABLE is used as parameter to call
zone_watermark_ok() in migrate_balanced_pgdat().  This makes it same
as requested zone in alloc_misplaced_dst_page().  So that
migrate_balanced_pgdat() returns false when memory pressure is heavy.

Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Rik van Riel <riel@...hat.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: Fengguang Wu <fengguang.wu@...el.com>
Cc: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org
---
 mm/migrate.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 513107baccd3..8f06bd37d927 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1954,7 +1954,7 @@ static bool migrate_balanced_pgdat(struct pglist_data *pgdat,
 		if (!zone_watermark_ok(zone, 0,
 				       high_wmark_pages(zone) +
 				       nr_migrate_pages,
-				       0, 0))
+				       ZONE_MOVABLE, 0))
 			continue;
 		return true;
 	}
-- 
2.23.0