diff mbox

mm: vmscan: do not throttle based on pfmemalloc reserves if node has no reclaimable zones

Message ID 20150327192850.GA18701@linux.vnet.ibm.com (mailing list archive)
State Superseded
Headers show

Commit Message

Nishanth Aravamudan March 27, 2015, 7:28 p.m. UTC 
Based upon 675becce15 ("mm: vmscan: do not throttle based on pfmemalloc
reserves if node has no ZONE_NORMAL") from Mel.

We have a system with the following topology:

(0) root @ br30p03: /root
# numactl -H
available: 3 nodes (0,2-3)
node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
23 24 25 26 27 28 29 30 31
node 0 size: 28273 MB
node 0 free: 27323 MB
node 2 cpus:
node 2 size: 16384 MB
node 2 free: 0 MB
node 3 cpus: 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47
node 3 size: 30533 MB
node 3 free: 13273 MB
node distances:
node   0   2   3 
  0:  10  20  20 
  2:  20  10  20 
  3:  20  20  10 

Node 2 has no free memory, because:

# cat /sys/devices/system/node/node2/hugepages/hugepages-16777216kB/nr_hugepages 
1

This leads to the following zoneinfo:

Node 2, zone      DMA
  pages free     0
        min      1840
        low      2300
        high     2760
        scanned  0
        spanned  262144
        present  262144
        managed  262144
...
  all_unreclaimable: 1

If one then attempts to allocate some normal 16M hugepages:

echo 37 > /proc/sys/vm/nr_hugepages

The echo enver returns and kswapd2 consumes CPU cycles.

This is because throttle_direct_reclaim ends up calling
wait_event(pfmemalloc_wait, pfmemalloc_watermark_ok...).
pfmemalloc_watermark_ok() in turn checks all zones on the node and see
if the there are any reserves, and if so, then indicates the watermarks
are ok, by seeing if there are sufficient free pages.

675becce15 added a condition already for memoryless nodes. In this case,
though, the node has memory, it is just all consumed (and not
recliamable). Effectively, though, the result is the same on this
call to pfmemalloc_watermark_ok() and thus seems like a reasonable
additional condition.

With this change, the afore-mentioned 16M hugepage allocation succeeds
and correctly round-robins between Nodes 1 and 3.

Signed-off-by: Nishanth Aravamudan <nacc@linux.vnet.ibm.com>

Comments

Nishanth Aravamudan March 27, 2015, 7:39 p.m. UTC | #1 
[ Sorry, typo'd anton's address ]

On 27.03.2015 [12:28:50 -0700], Nishanth Aravamudan wrote:
> Based upon 675becce15 ("mm: vmscan: do not throttle based on pfmemalloc
> reserves if node has no ZONE_NORMAL") from Mel.
> 
> We have a system with the following topology:
> 
> (0) root @ br30p03: /root
> # numactl -H
> available: 3 nodes (0,2-3)
> node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
> 23 24 25 26 27 28 29 30 31
> node 0 size: 28273 MB
> node 0 free: 27323 MB
> node 2 cpus:
> node 2 size: 16384 MB
> node 2 free: 0 MB
> node 3 cpus: 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47
> node 3 size: 30533 MB
> node 3 free: 13273 MB
> node distances:
> node   0   2   3 
>   0:  10  20  20 
>   2:  20  10  20 
>   3:  20  20  10 
> 
> Node 2 has no free memory, because:
> 
> # cat /sys/devices/system/node/node2/hugepages/hugepages-16777216kB/nr_hugepages 
> 1
> 
> This leads to the following zoneinfo:
> 
> Node 2, zone      DMA
>   pages free     0
>         min      1840
>         low      2300
>         high     2760
>         scanned  0
>         spanned  262144
>         present  262144
>         managed  262144
> ...
>   all_unreclaimable: 1
> 
> If one then attempts to allocate some normal 16M hugepages:
> 
> echo 37 > /proc/sys/vm/nr_hugepages
> 
> The echo enver returns and kswapd2 consumes CPU cycles.
> 
> This is because throttle_direct_reclaim ends up calling
> wait_event(pfmemalloc_wait, pfmemalloc_watermark_ok...).
> pfmemalloc_watermark_ok() in turn checks all zones on the node and see
> if the there are any reserves, and if so, then indicates the watermarks
> are ok, by seeing if there are sufficient free pages.
> 
> 675becce15 added a condition already for memoryless nodes. In this case,
> though, the node has memory, it is just all consumed (and not
> recliamable). Effectively, though, the result is the same on this
> call to pfmemalloc_watermark_ok() and thus seems like a reasonable
> additional condition.
> 
> With this change, the afore-mentioned 16M hugepage allocation succeeds
> and correctly round-robins between Nodes 1 and 3.
> 
> Signed-off-by: Nishanth Aravamudan <nacc@linux.vnet.ibm.com>
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index dcd90c8..033c2b7 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2585,7 +2585,7 @@ static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
>  
>         for (i = 0; i <= ZONE_NORMAL; i++) {
>                 zone = &pgdat->node_zones[i];
> -               if (!populated_zone(zone))
> +               if (!populated_zone(zone) || !zone_reclaimable(zone))
>                         continue;
>  
>                 pfmemalloc_reserve += min_wmark_pages(zone);
>
Dan Streetman March 27, 2015, 7:58 p.m. UTC | #2 
On Fri, Mar 27, 2015 at 3:28 PM, Nishanth Aravamudan
<nacc@linux.vnet.ibm.com> wrote:
> Based upon 675becce15 ("mm: vmscan: do not throttle based on pfmemalloc
> reserves if node has no ZONE_NORMAL") from Mel.
>
> We have a system with the following topology:
>
> (0) root @ br30p03: /root
> # numactl -H
> available: 3 nodes (0,2-3)
> node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
> 23 24 25 26 27 28 29 30 31
> node 0 size: 28273 MB
> node 0 free: 27323 MB
> node 2 cpus:
> node 2 size: 16384 MB
> node 2 free: 0 MB
> node 3 cpus: 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47
> node 3 size: 30533 MB
> node 3 free: 13273 MB
> node distances:
> node   0   2   3
>   0:  10  20  20
>   2:  20  10  20
>   3:  20  20  10
>
> Node 2 has no free memory, because:
>
> # cat /sys/devices/system/node/node2/hugepages/hugepages-16777216kB/nr_hugepages
> 1
>
> This leads to the following zoneinfo:
>
> Node 2, zone      DMA
>   pages free     0
>         min      1840
>         low      2300
>         high     2760
>         scanned  0
>         spanned  262144
>         present  262144
>         managed  262144
> ...
>   all_unreclaimable: 1
>
> If one then attempts to allocate some normal 16M hugepages:
>
> echo 37 > /proc/sys/vm/nr_hugepages
>
> The echo enver returns and kswapd2 consumes CPU cycles.
>
> This is because throttle_direct_reclaim ends up calling
> wait_event(pfmemalloc_wait, pfmemalloc_watermark_ok...).
> pfmemalloc_watermark_ok() in turn checks all zones on the node and see
> if the there are any reserves, and if so, then indicates the watermarks
> are ok, by seeing if there are sufficient free pages.
>
> 675becce15 added a condition already for memoryless nodes. In this case,
> though, the node has memory, it is just all consumed (and not
> recliamable). Effectively, though, the result is the same on this
> call to pfmemalloc_watermark_ok() and thus seems like a reasonable
> additional condition.
>
> With this change, the afore-mentioned 16M hugepage allocation succeeds
> and correctly round-robins between Nodes 1 and 3.
>
> Signed-off-by: Nishanth Aravamudan <nacc@linux.vnet.ibm.com>

Reviewed-by: Dan Streetman <ddstreet@ieee.org>

>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index dcd90c8..033c2b7 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2585,7 +2585,7 @@ static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
>
>         for (i = 0; i <= ZONE_NORMAL; i++) {
>                 zone = &pgdat->node_zones[i];
> -               if (!populated_zone(zone))
> +               if (!populated_zone(zone) || !zone_reclaimable(zone))
>                         continue;
>
>                 pfmemalloc_reserve += min_wmark_pages(zone);
>
Dave Hansen March 27, 2015, 8:17 p.m. UTC | #3 
On 03/27/2015 12:28 PM, Nishanth Aravamudan wrote:
> @@ -2585,7 +2585,7 @@ static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
>  
>         for (i = 0; i <= ZONE_NORMAL; i++) {
>                 zone = &pgdat->node_zones[i];
> -               if (!populated_zone(zone))
> +               if (!populated_zone(zone) || !zone_reclaimable(zone))
>                         continue;
>  
>                 pfmemalloc_reserve += min_wmark_pages(zone);

Do you really want zone_reclaimable()?  Or do you want something more
direct like "zone_reclaimable_pages(zone) == 0"?
diff mbox

Patch

diff --git a/mm/vmscan.c b/mm/vmscan.c
index dcd90c8..033c2b7 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2585,7 +2585,7 @@  static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
 
        for (i = 0; i <= ZONE_NORMAL; i++) {
                zone = &pgdat->node_zones[i];
-               if (!populated_zone(zone))
+               if (!populated_zone(zone) || !zone_reclaimable(zone))
                        continue;
 
                pfmemalloc_reserve += min_wmark_pages(zone);