Re: [PATCH] mm:page_alloc: fix the NULL ac->nodemask in __alloc_pages_slowpath()

[Michal Hocko <mhocko@suse.com>]

On Wed 21-08-24 21:59:00, Zhongkun He wrote:
> I found a problem in my test machine that should_reclaim_retry() do
> not get the right node if i set the cpuset.mems
> 
> 1.Test step and the machines.
> ------------
> root@vm:/sys/fs/cgroup/test# numactl -H | grep size
> node 0 size: 9477 MB
> node 1 size: 10079 MB
> node 2 size: 10079 MB
> node 3 size: 10078 MB
> 
> root@vm:/sys/fs/cgroup/test# cat cpuset.mems
>     2
> 
> root@vm:/sys/fs/cgroup/test# stress --vm 1 --vm-bytes 12g  --vm-keep
> stress: info: [33430] dispatching hogs: 0 cpu, 0 io, 1 vm, 0 hdd
> stress: FAIL: [33430] (425) <-- worker 33431 got signal 9
> stress: WARN: [33430] (427) now reaping child worker processes
> stress: FAIL: [33430] (461) failed run completed in 2s

OK, so the test gets killed as expected.

> 2. reclaim_retry_zone info:
> 
> We can only alloc pages from node=2, but the reclaim_retry_zone is
> node=0 and return true.
> 
> root@vm:/sys/kernel/debug/tracing# cat trace
> stress-33431   [001] ..... 13223.617311: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=1 wmark_check=1
> stress-33431   [001] ..... 13223.617682: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=2 wmark_check=1
> stress-33431   [001] ..... 13223.618103: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=3 wmark_check=1
> stress-33431   [001] ..... 13223.618454: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=4 wmark_check=1
> stress-33431   [001] ..... 13223.618770: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=5 wmark_check=1
> stress-33431   [001] ..... 13223.619150: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=6 wmark_check=1
> stress-33431   [001] ..... 13223.619510: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=7 wmark_check=1
> stress-33431   [001] ..... 13223.619850: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=8 wmark_check=1
> stress-33431   [001] ..... 13223.620171: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=9 wmark_check=1
> stress-33431   [001] ..... 13223.620533: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=10 wmark_check=1
> stress-33431   [001] ..... 13223.620894: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=11 wmark_check=1
> stress-33431   [001] ..... 13223.621224: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=12 wmark_check=1
> stress-33431   [001] ..... 13223.621551: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=13 wmark_check=1
> stress-33431   [001] ..... 13223.621847: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=14 wmark_check=1
> stress-33431   [001] ..... 13223.622200: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=15 wmark_check=1
> stress-33431   [001] ..... 13223.622580: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=16 wmark_check=1

Are you suggesting that the problem is that should_reclaim_retry is
iterating nodes which are not allowed by cpusets and that makes the
retry loop happening more than unnecessary?

Is there any reason why you haven't done the same that the page
allocator does in this case?
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 28f80daf5c04..cbf09c0e3b8a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4098,6 +4098,11 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order,
 		unsigned long min_wmark = min_wmark_pages(zone);
 		bool wmark;
 
+		if (cpusets_enabled() &&
+			(alloc_flags & ALLOC_CPUSET) &&
+			!__cpuset_zone_allowed(zone, gfp_mask))
+				continue;
+
 		available = reclaimable = zone_reclaimable_pages(zone);
 		available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
 
-- 
Michal Hocko
SUSE Labs