Re: [PATCH v2] mm/mempolicy: track page allocations per mempolicy

["JP Kobryn (Meta)" <jp.kobryn@linux.dev>]

On 3/8/26 12:24 PM, Usama Arif wrote:
> On Fri,  6 Mar 2026 20:55:20 -0800 "JP Kobryn (Meta)" <jp.kobryn@linux.dev> wrote:
[...]
>> +static void mpol_count_numa_alloc(struct mempolicy *pol, int intended_nid,
>> +				  struct page *page, unsigned int order)
>> +{
>> +	int actual_nid = page_to_nid(page);
>> +	long nr_pages = 1L << order;
>> +	enum node_stat_item hit_idx;
>> +	struct mem_cgroup *memcg;
>> +	struct lruvec *lruvec;
>> +	bool is_hit;
>> +
>> +	if (!root_mem_cgroup || mem_cgroup_disabled())
>> +		return;
> 
> Hello JP!
> 
> The stats are exposed via /proc/vmstat and are guarded by CONFIG_NUMA, not
> CONFIG_MEMCG. Early returning overhere would make it inaccuate. Does
> it make sense to use mod_node_page_state if memcg is not available,
> so that these global counters work regardless of cgroup configuration.
>

Good call. I can instead do:

if (!mem_cgroup_disabled() && root_mem_cgroup) {
	struct mem_cgroup *memcg;
	struct lruvec *lruvec;
	/* use lruvec for updating stats */
} else {
	/* use node for updating stats */
}

This should also take care of the bot warning on mem_cgroup_from_task()
not being available.