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

[Johannes Weiner <hannes@cmpxchg.org>]

On Sun, Mar 08, 2026 at 08:30:47PM -0700, JP Kobryn (Meta) wrote:
> 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.

mem_cgroup_lruvec() and mod_lruvec_state() already do the right thing
for !CONFIG_MEMCG. Add a dummy for mem_cgroup_from_task() and you can
do a single, shared sequence for both configs.