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SubjectRe: [PATCH] mm/thp: don't count ZONE_MOVABLE as the target for freepage reserving
On Thu 05-04-18 16:27:16, Joonsoo Kim wrote:
> 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.

OK, but why does it matter. Has anybody seen this as an issue?

> 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
>

--
Michal Hocko
SUSE Labs

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