From f63661566fad43c0884ad879e6ff07c55ed890f4 Mon Sep 17 00:00:00 2001
From: Baoquan He <bhe@redhat.com>
Date: Wed, 3 Jun 2020 15:58:52 -0700
Subject: [PATCH] mm/page_alloc.c: clear out zone->lowmem_reserve[] if the zone
is empty
When requesting memory allocation from a specific zone is not satisfied,
it will fall to lower zone to try allocating memory. In this case, lower
zone's ->lowmem_reserve[] will help protect its own memory resource. The
higher the relevant ->lowmem_reserve[] is, the harder the upper zone can
get memory from this lower zone.
However, this protection mechanism should be applied to populated zone,
but not an empty zone. So filling ->lowmem_reserve[] for empty zone is
not necessary, and may mislead people that it's valid data in that zone.
Node 2, zone DMA
pages free 0
min 0
low 0
high 0
spanned 0
present 0
managed 0
protection: (0, 0, 1024, 1024)
Node 2, zone DMA32
pages free 0
min 0
low 0
high 0
spanned 0
present 0
managed 0
protection: (0, 0, 1024, 1024)
Node 2, zone Normal
per-node stats
nr_inactive_anon 0
nr_active_anon 143
nr_inactive_file 0
nr_active_file 0
nr_unevictable 0
nr_slab_reclaimable 45
nr_slab_unreclaimable 254
Here clear out zone->lowmem_reserve[] if zone is empty.
Signed-off-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20200402140113.3696-3-bhe@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
mm/page_alloc.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f3d5f0eb615915..5b8d0966d4291f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7704,8 +7704,10 @@ static void setup_per_zone_lowmem_reserve(void)
idx--;
lower_zone = pgdat->node_zones + idx;
- if (!sysctl_lowmem_reserve_ratio[idx]) {
+ if (!sysctl_lowmem_reserve_ratio[idx] ||
+ !zone_managed_pages(lower_zone)) {
lower_zone->lowmem_reserve[j] = 0;
+ continue;
} else {
lower_zone->lowmem_reserve[j] =
managed_pages / sysctl_lowmem_reserve_ratio[idx];
--
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