On 2021/5/28 7:47, Baoquan He wrote:

On 05/27/21 at 08:57pm, Liu Shixin wrote:

quoted

The commit f63661566fad (mm/page_alloc.c: clear out zone->lowmem_reserve[]
if the zone is empty) clear out zone->lowmem_reserve[] if zone is empty.
But when zone is not empty and sysctl_lowmem_reserve_ratio[i] is set to zero,
zone_managed_pages(zone) is not counted in the managed_pages either. This is
inconsistent with the description of lowmen_reserve, so fix it.

Right, this is a good catch. Thanks for the fixing. 

Is it worth adding words in Documentation/admin-guide/sysctl/vm.rst
to notice this?

Reviewed-by: Baoquan He <redacted>

Thanks
Baoquan

With this patch, It's consistent with the calculation description of zone[i]'s protection[j].

This is implicit in the description so I don't think it's necessary to notice this.

quoted

Fixes: f63661566fad ("mm/page_alloc.c: clear out zone->lowmem_reserve[] if the zone is empty")
Reported-by: yangerkun <redacted>
Signed-off-by: Liu Shixin <redacted>
---
 mm/page_alloc.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index aaa1655cf682..49a2efce5a84 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c

@@ -8061,14 +8061,14 @@ static void setup_per_zone_lowmem_reserve(void)
 			unsigned long managed_pages = 0;
 
 			for (j = i + 1; j < MAX_NR_ZONES; j++) {
-				if (clear) {
-					zone->lowmem_reserve[j] = 0;
-				} else {
-					struct zone *upper_zone = &pgdat->node_zones[j];
+				struct zone *upper_zone = &pgdat->node_zones[j];
+
+				managed_pages += zone_managed_pages(upper_zone);
 
-					managed_pages += zone_managed_pages(upper_zone);
+				if (clear)
+					zone->lowmem_reserve[j] = 0;
+				else
 					zone->lowmem_reserve[j] = managed_pages / ratio;
-				}
 			}
 		}
 	}

-- 
2.18.0.huawei.25

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