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Subject[PATCH] mm/thp: don't count ZONE_MOVABLE as the target for freepage reserving
Date
From: Joonsoo Kim <iamjoonsoo.kim@lge.com>

ZONE_MOVABLE only has movable pages so we don't need to keep enough
freepages to avoid or deal with fragmentation. So, don't count it.

This changes min_free_kbytes and thus min_watermark greatly
if ZONE_MOVABLE is used. It will make the user uses more memory.

o System
22GB ram, fakenuma, 2 nodes. 5 zones are used.

o Before
min_free_kbytes: 112640

zone_info (min_watermark):
Node 0, zone DMA
min 19
Node 0, zone DMA32
min 3778
Node 0, zone Normal
min 10191
Node 0, zone Movable
min 0
Node 0, zone Device
min 0
Node 1, zone DMA
min 0
Node 1, zone DMA32
min 0
Node 1, zone Normal
min 14043
Node 1, zone Movable
min 127
Node 1, zone Device
min 0

o After
min_free_kbytes: 90112

zone_info (min_watermark):
Node 0, zone DMA
min 15
Node 0, zone DMA32
min 3022
Node 0, zone Normal
min 8152
Node 0, zone Movable
min 0
Node 0, zone Device
min 0
Node 1, zone DMA
min 0
Node 1, zone DMA32
min 0
Node 1, zone Normal
min 11234
Node 1, zone Movable
min 102
Node 1, zone Device
min 0

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
---
mm/khugepaged.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 5de1c6f..92dd4e6 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1880,8 +1880,16 @@ static void set_recommended_min_free_kbytes(void)
int nr_zones = 0;
unsigned long recommended_min;

- for_each_populated_zone(zone)
+ for_each_populated_zone(zone) {
+ /*
+ * We don't need to worry about fragmentation of
+ * ZONE_MOVABLE since it only has movable pages.
+ */
+ if (zone_idx(zone) > gfp_zone(GFP_USER))
+ continue;
+
nr_zones++;
+ }

/* Ensure 2 pageblocks are free to assist fragmentation avoidance */
recommended_min = pageblock_nr_pages * nr_zones * 2;
--
2.7.4
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