In a numa server, topology looks like
available: 3 nodes (0,2-3)
node 0 cpus:
node 0 size: 0 MB
node 0 free: 0 MB
node 2 cpus: 0 1 2 3 4 5 6 7
node 2 size: 15299 MB
node 2 free: 289 MB
node 3 cpus:
node 3 size: 15336 MB
node 3 free: 184 MB
node distances:
node 0 2 3
0: 10 40 40
2: 40 10 20
3: 40 20 10
When I try to dynamically allocate the hugepages more than system total free
memory:
e.g. echo 4000 >/proc/sys/vm/nr_hugepages
Then the kswapd will take 100% cpu for a long time(more than 3 hours, and will
not be about to end)
top result:
top - 13:42:59 up 3:37, 1 user, load average: 1.09, 1.03, 1.01
Tasks: 1 total, 1 running, 0 sleeping, 0 stopped, 0 zombie
%Cpu(s): 0.0 us, 12.5 sy, 0.0 ni, 85.5 id, 2.0 wa, 0.0 hi, 0.0 si, 0.0 st
KiB Mem: 31371520 total, 30915136 used, 456384 free, 320 buffers
KiB Swap: 6284224 total, 115712 used, 6168512 free. 48192 cached Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
76 root 20 0 0 0 0 R 100.0 0.000 217:17.29 kswapd3
The root cause is: kswapd3 is waken up and then try to do reclaim again and
again but it makes no progress. At last the allocated hugepages are less than
4000.
HugePages_Total: 1864
HugePages_Free: 1864
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 16384 kB
At that time, even there are no relaimable pages in that node3, kswapd3 will
not go to sleep.
Node 3, zone DMA
per-node stats
nr_inactive_anon 0
nr_active_anon 0
nr_inactive_file 0
nr_active_file 0
nr_unevictable 0
nr_isolated_anon 0
nr_isolated_file 0
nr_pages_scanned 0
workingset_refault 0
workingset_activate 0
workingset_nodereclaim 0
nr_anon_pages 0
nr_mapped 0
nr_file_pages 0
nr_dirty 0
nr_writeback 0
nr_writeback_temp 0
nr_shmem 0
nr_shmem_hugepages 0
nr_shmem_pmdmapped 0
nr_anon_transparent_hugepages 0
nr_unstable 0
nr_vmscan_write 0
nr_vmscan_immediate_reclaim 0
nr_dirtied 0
nr_written 0
pages free 2951
min 2821
low 3526
high 4231
node_scanned 0
spanned 245760
present 245760
managed 245388
nr_free_pages 2951
nr_zone_inactive_anon 0
nr_zone_active_anon 0
nr_zone_inactive_file 0
nr_zone_active_file 0
nr_zone_unevictable 0
nr_zone_write_pending 0
nr_mlock 0
nr_slab_reclaimable 46
nr_slab_unreclaimable 90
nr_page_table_pages 0
nr_kernel_stack 0
nr_bounce 0
nr_zspages 0
numa_hit 2257
numa_miss 0
numa_foreign 0
numa_interleave 982
numa_local 0
numa_other 2257
nr_free_cma 0
protection: (0, 0, 0, 0)
It would be called a misconfiguration but it seems that it might be quite easy
to hit with NUMA machines which have large differences in the node sizes.
Further more, when it consumes most the memory in node3, every alloc slow path
might wake up kswapd3 and it will make things worse:
__alloc_pages_slowpath
wake_all_kswapds
wakeup_kswapd
This patch resolves the issue from 2 aspects:
1. In prepare_kswapd_sleep, only when zone is not balanced and there are
reclaimable pages in this zone, kswapd will go to do relaim without sleeping
2. Don't wake up kswapd if there are no reclaimable pages in that node
After this patch:
top - 07:29:43 up 3 min, 1 user, load average: 0.12, 0.13, 0.06
Tasks: 1 total, 0 running, 1 sleeping, 0 stopped, 0 zombie
%Cpu(s): 0.0 us, 0.2 sy, 0.0 ni, 97.8 id, 2.0 wa, 0.0 hi, 0.0 si, 0.0 st
KiB Mem: 31371520 total, 938112 used, 30433408 free, 5504 buffers
KiB Swap: 6284224 total, 0 used, 6284224 free. 632448 cached Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
78 root 20 0 0 0 0 S 0.000 0.000 0:00.00 kswapd3
Changes:
V2: - fix incorrect condition for assignment of node_has_reclaimable_pages
- make commit decription better
Signed-off-by: Jia He <hejia...@gmail.com>
---
mm/vmscan.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 532a2a7..7c5a563 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3139,7 +3139,8 @@ static bool prepare_kswapd_sleep(pg_data_t *pgdat, int
order, int classzone_idx)
if (!managed_zone(zone))
continue;
- if (!zone_balanced(zone, order, classzone_idx))
+ if (!zone_balanced(zone, order, classzone_idx)
+ && zone_reclaimable_pages(zone))
return false;
}
@@ -3502,6 +3503,7 @@ void wakeup_kswapd(struct zone *zone, int order, enum
zone_type classzone_idx)
{
pg_data_t *pgdat;
int z;
+ int node_has_relaimable_pages = 0;
if (!managed_zone(zone))
return;
@@ -3522,8 +3524,15 @@ void wakeup_kswapd(struct zone *zone, int order, enum
zone_type classzone_idx)
if (zone_balanced(zone, order, classzone_idx))
return;
+
+ if (zone_reclaimable_pages(zone))
+ node_has_relaimable_pages = 1;
}
+ /* Dont wake kswapd if all zones has no reclaimable pages */
+ if (!node_has_relaimable_pages)
+ return;
+
trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
wake_up_interruptible(&pgdat->kswapd_wait);
}
--
1.8.5.6
