From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Subject: mm/thp: don't count ZONE_MOVABLE as the target for freepage reserving
There was a regression report for "mm/cma: manage the memory of the CMA
area by using the ZONE_MOVABLE"
(lkml.kernel.org/r/20180102063528.GG30397%20()%20yexl-desktop) and I think
that it is related to this problem. CMA patchset makes the system use
one more zone (ZONE_MOVABLE) and then increases min_free_kbytes. It
reduces usable memory and it could cause regression.
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
Link: http://lkml.kernel.org/r/1522913236-15776-1-git-send-email-iamjoonsoo.kim@xxxxxxx
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: "Kirill A . Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/khugepaged.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff -puN mm/khugepaged.c~mm-thp-dont-count-zone_movable-as-the-target-for-freepage-reserving mm/khugepaged.c
--- a/mm/khugepaged.c~mm-thp-dont-count-zone_movable-as-the-target-for-freepage-reserving
+++ a/mm/khugepaged.c
@@ -1879,8 +1879,16 @@ static void set_recommended_min_free_kby
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;
_
--
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