The patch titled
Subject: mm/page_alloc.c: clear out zone->lowmem_reserve[] if the zone is empty
has been added to the -mm tree. Its filename is
mm-page_allocc-clear-out-zone-lowmem_reserve-if-the-zone-is-empty.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-page_allocc-clear-out-zone-lowmem_reserve-if-the-zone-is-empty.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-page_allocc-clear-out-zone-lowmem_reserve-if-the-zone-is-empty.patch
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------------------------------------------------------
From: Baoquan He <bhe@xxxxxxxxxx>
Subject: 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.
Link: http://lkml.kernel.org/r/20200402140113.3696-3-bhe@xxxxxxxxxx
Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
--- a/mm/page_alloc.c~mm-page_allocc-clear-out-zone-lowmem_reserve-if-the-zone-is-empty
+++ a/mm/page_alloc.c
@@ -7702,8 +7702,10 @@ static void setup_per_zone_lowmem_reserv
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];
_
Patches currently in -mm which might be from bhe@xxxxxxxxxx are
mm-memmap_init-iterate-over-memblock-regions-rather-that-check-each-pfn.patch
mm-remove-unused-free_bootmem_with_active_regions.patch
mm-page_allocc-only-tune-sysctl_lowmem_reserve_ratio-value-once-when-changing-it.patch
mm-page_allocc-clear-out-zone-lowmem_reserve-if-the-zone-is-empty.patch
mm-vmstatc-do-not-show-lowmem-reserve-protection-information-of-empty-zone.patch
