Re: [PATCH V1] mm:page_alloc: fix the NULL ac->nodemask in __alloc_pages_slowpath()

[Michal Hocko <mhocko@suse.com>]

On Thu 22-08-24 16:38:42, 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.
> The should_reclaim_retry() and try_to_compact_pages() are iterating
> nodes which are not allowed by cpusets and that makes the retry loop
> happening more than unnecessary.

I would update the problem description because from the above it is not
really clear what the actual problem is.

should_reclaim_retry is not ALLOC_CPUSET aware and that means that it
considers reclaimability of NUMA nodes which are outside of the cpuset.
If other nodes have a lot of reclaimable memory then should_reclaim_retry
would instruct page allocator to retry even though there is no memory
reclaimable on the cpuset nodemask. This is not really a huge problem
because the number of retries without any reclaim progress is bound but
it could be certainly improved. This is a cold path so this shouldn't
really have a measurable impact on performance on most workloads.

> 
> 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
> 
> 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
> 

You can drop the following

> 3. Root cause:
> Nodemask usually comes from mempolicy in policy_nodemask(), which
> is always NULL unless the memory policy is bind or prefer_many.
> 
> nodemask = NULL
> __alloc_pages_noprof()
> 	prepare_alloc_pages
> 		ac->nodemask = &cpuset_current_mems_allowed;
> 
> 	get_page_from_freelist()
> 
> 	ac.nodemask = nodemask;  /*set  NULL*/
> 
> 	__alloc_pages_slowpath() {
> 		f (!(alloc_flags & ALLOC_CPUSET) || reserve_flags) {
> 			ac->nodemask = NULL;
> 			ac->preferred_zoneref = first_zones_zonelist(ac->zonelist,
> 					ac->highest_zoneidx, ac->nodemask);
> 
> 		/* so ac.nodemask = NULL */
> 	}
> 
> According to the function flow above, we do not have the memory limit to
> follow cpuset.mems, so we need to add it.
> 
> Test result:
> Try 3 times with different cpuset.mems and alloc large memorys than that numa size.
> echo 1 > cpuset.mems
> stress --vm 1 --vm-bytes 12g --vm-hang 0
> ---------------
> echo 2 > cpuset.mems
> stress --vm 1 --vm-bytes 12g --vm-hang 0
> ---------------
> echo 3 > cpuset.mems
> stress --vm 1 --vm-bytes 12g --vm-hang 0
> 
> The retry trace look like:
> stress-2139    [003] .....   666.934104: reclaim_retry_zone: node=1 zone=Normal   order=0 reclaimable=7 available=7355 min_wmark=8598 no_progress_loops=1 wmark_check=0
> stress-2204    [010] .....   695.447393: reclaim_retry_zone: node=2 zone=Normal   order=0 reclaimable=2 available=6916 min_wmark=8598 no_progress_loops=1 wmark_check=0
> stress-2271    [008] .....   725.683058: reclaim_retry_zone: node=3 zone=Normal   order=0 reclaimable=17 available=8079 min_wmark=8597 no_progress_loops=1 wmark_check=0
> 

And only keep this

> With this patch, we can check the right node and get less retry in __alloc_pages_slowpath()
> because there is nothing to do.
> 
> V1:
> Do the same with the page allocator using __cpuset_zone_allowed().
> 
> Suggested-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Zhongkun He <hezhongkun.hzk@bytedance.com>

With those changes you can add
Acked-by: Michal Hocko <mhocko@suse.com>
Thanks!

> ---
>  mm/compaction.c | 6 ++++++
>  mm/page_alloc.c | 5 +++++
>  2 files changed, 11 insertions(+)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index d1041fbce679..a2b16b08cbbf 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -23,6 +23,7 @@
>  #include <linux/freezer.h>
>  #include <linux/page_owner.h>
>  #include <linux/psi.h>
> +#include <linux/cpuset.h>
>  #include "internal.h"
>  
>  #ifdef CONFIG_COMPACTION
> @@ -2822,6 +2823,11 @@ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
>  					ac->highest_zoneidx, ac->nodemask) {
>  		enum compact_result status;
>  
> +		if (cpusets_enabled() &&
> +			(alloc_flags & ALLOC_CPUSET) &&
> +			!__cpuset_zone_allowed(zone, gfp_mask))
> +				continue;
> +
>  		if (prio > MIN_COMPACT_PRIORITY
>  					&& compaction_deferred(zone, order)) {
>  			rc = max_t(enum compact_result, COMPACT_DEFERRED, rc);
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 29608ca294cf..8a67d760b71a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4128,6 +4128,11 @@ 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);
>  
> -- 
> 2.20.1

-- 
Michal Hocko
SUSE Labs