Re: [PATCH v2] mm: move pgscan and pgsteal to node stats

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

On 2/18/26 10:02 AM, JP Kobryn (Meta) wrote:
> On 2/18/26 12:54 AM, Vlastimil Babka (SUSE) wrote:
>> On 2/18/26 04:29, JP Kobryn (Meta) wrote:
>>> From: JP Kobryn <jp.kobryn@linux.dev>
>>>
>>> There are situations where reclaim kicks in on a system with free 
>>> memory.
>>> One possible cause is a NUMA imbalance scenario where one or more 
>>> nodes are
>>> under pressure. It would help if we could easily identify such nodes.
>>>
>>> Move the pgscan and pgsteal counters from vm_event_item to 
>>> node_stat_item
>>> to provide per-node reclaim visibility. With these counters as node 
>>> stats,
>>> the values are now displayed in the per-node section of /proc/zoneinfo,
>>> which allows for quick identification of the affected nodes.
>>>
>>> /proc/vmstat continues to report the same counters, aggregated across 
>>> all
>>> nodes. But the ordering of these items within the readout changes as 
>>> they
>>> move from the vm events section to the node stats section.
>>>
>>> Memcg accounting of these counters is preserved. The relocated counters
>>> remain visible in memory.stat alongside the existing aggregate pgscan 
>>> and
>>> pgsteal counters.
>>>
>>> However, this change affects how the global counters are accumulated.
>>> Previously, the global event count update was gated on ! 
>>> cgroup_reclaim(),
>>> excluding memcg-based reclaim from /proc/vmstat. Now that
>>> mod_lruvec_state() is being used to update the counters, the global
>>> counters will include all reclaim. This is consistent with how pgdemote
>>> counters are already tracked.
>>
>> Hm so that leaves PGREFILL (scanned in the active list) the odd one out,
>> right? Not being per-node and gated on !cgroup_reclaim() for global 
>> stats.
>> Should we change it too for full consistency?
> 
> I'm fine with adding coverage for the active list side as well. For
> completeness, I could also include PGDEACTIVATE.

Actually, I see PGDEACTIVATE is not gated so I'll leave that one out.
I'll send v3 and include PGREFILL.