Re: [PATCH v5 20/36] mm/memcontrol: account private-node memory in per-node stats

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [Medium] The patch updates `mem_cgroup_css_rstat_flush` to include `N_MEMORY_PRIVATE` nodes, but misses `flush_nmi_stats()` which still strictly iterates over `N_MEMORY`, leaking NMI slab stats on private nodes.
- [Medium] `hugetlb_cgroup_read_numa_stat()` in the hugetlb cgroup controller skips `N_MEMORY_PRIVATE` nodes, leading to hidden node memory and incorrect hierarchical totals.
--

--- Patch [20]: [PATCH v5 20/36] mm/memcontrol: account private-node memory in per-node stats ---
commit 923e253e1d279f965b728ad3baafd46c0f7044eb
Author: Gregory Price <gourry@gourry.net>

mm/memcontrol: account private-node memory in per-node stats

Private nodes folios are charged like any other - the node's per-cpu
lruvec counters are increment even for N_MEMORY_PRIVATE.

[ ... ]

> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index f0dde52dc9e0e..4d79e238bc57d 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4496,6 +4496,7 @@ static void mem_cgroup_css_rstat_flush(struct cgroup_subsys_state *css, int cpu)
>  	struct mem_cgroup *parent = parent_mem_cgroup(memcg);
>  	struct memcg_vmstats_percpu *statc;
>  	struct aggregate_control ac;
> +	nodemask_t reportable;
>  	int nid;
>  
>  	flush_nmi_stats(memcg, parent);

[Severity: Medium]
Will this still leak NMI slab stats on private nodes?

flush_nmi_stats() still strictly iterates over N_MEMORY instead of including
N_MEMORY_PRIVATE.

If a slab allocation occurs in NMI context on an N_MEMORY_PRIVATE node, the
node-local atomic counter is incremented, but it appears flush_nmi_stats()
will fail to drain it because it only iterates over N_MEMORY.

[ ... ]

[Severity: Medium]
Does mm/hugetlb_cgroup.c:hugetlb_cgroup_read_numa_stat() also need to be
updated to include N_MEMORY_PRIVATE?

It currently only covers N_MEMORY when calculating and printing per-node
hierarchical usage:

	for_each_node_state(nid, N_MEMORY) {
		usage = 0;
		...

If hugetlb memory is allocated on an N_MEMORY_PRIVATE node and charged to a
cgroup, reading the cgroup's NUMA stat file would skip accumulating or
displaying this node's usage.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260720193431.3841992-1-gourry@gourry.net?part=20