From: Joonsoo Kim <[email protected]>
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 <[email protected]>
---
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
On Thu 05-04-18 16:27:16, Joonsoo Kim wrote:
> From: Joonsoo Kim <[email protected]>
>
> 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 <[email protected]>
> ---
> 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
On Thu, Apr 05, 2018 at 09:57:53AM +0200, Michal Hocko wrote:
> On Thu 05-04-18 16:27:16, Joonsoo Kim wrote:
> > From: Joonsoo Kim <[email protected]>
> >
> > 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?
There was a regression report for CMA patchset and I think that it is
related to this problem. CMA patchset makes the system uses one more
zone (ZONE_MOVABLE) and then increase min_free_kbytes. It reduces
usable memory and it could cause regression.
http://lkml.kernel.org/r/20180102063528.GG30397@yexl-desktop
Thanks.
On Thu, Apr 05, 2018 at 05:05:39PM +0900, Joonsoo Kim wrote:
> On Thu, Apr 05, 2018 at 09:57:53AM +0200, Michal Hocko wrote:
> > On Thu 05-04-18 16:27:16, Joonsoo Kim wrote:
> > > From: Joonsoo Kim <[email protected]>
> > >
> > > 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.
Oops.. s/more/less
> >
> > OK, but why does it matter. Has anybody seen this as an issue?
>
> There was a regression report for CMA patchset and I think that it is
> related to this problem. CMA patchset makes the system uses one more
> zone (ZONE_MOVABLE) and then increase min_free_kbytes. It reduces
> usable memory and it could cause regression.
>
> http://lkml.kernel.org/r/20180102063528.GG30397@yexl-desktop
Thanks.
On Thu 05-04-18 17:05:39, Joonsoo Kim wrote:
> On Thu, Apr 05, 2018 at 09:57:53AM +0200, Michal Hocko wrote:
> > On Thu 05-04-18 16:27:16, Joonsoo Kim wrote:
> > > From: Joonsoo Kim <[email protected]>
> > >
> > > 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?
>
> There was a regression report for CMA patchset and I think that it is
> related to this problem. CMA patchset makes the system uses one more
> zone (ZONE_MOVABLE) and then increase min_free_kbytes. It reduces
> usable memory and it could cause regression.
>
> http://lkml.kernel.org/r/20180102063528.GG30397@yexl-desktop
Then this should be a part of the changelog along with some reproducible
results, please.
--
Michal Hocko
SUSE Labs