Re: [PATCH] memory tiering: Do not allow promotion if NUMA_BALANCING_MEMORY_TIERING is disabled

[Andrew Morton]

On Fri, 20 Mar 2026 14:52:51 +0530 Donet Tom <donettom@xxxxxxxxxxxxx> wrote:

> In the current implementation, if NUMA_BALANCING_MEMORY_TIERING is
> disabled and the pages are on the lower tier, the pages may still be
> promoted.
> 
> This happens because task_numa_work() updates the last_cpupid field to
> record the last access time only when NUMA_BALANCING_MEMORY_TIERING is
> enabled and the folio is on the lower tier. If
> NUMA_BALANCING_MEMORY_TIERING is disabled, the last_cpupid field
> retains a valid last CPU id.
> 
> In should_numa_migrate_memory(), the decision checks whether
> NUMA_BALANCING_MEMORY_TIERING is disabled, the folio is on the lower
> tier, and last_cpupid is invalid. However, since last_cpupid remains
> valid when NUMA_BALANCING_MEMORY_TIERING is disabled, the condition
> evaluates to false and migration is allowed.
> 
> This patch prevents promotion when NUMA_BALANCING_MEMORY_TIERING is
> disabled and the folio is on the lower tier.

Thanks.  The AI reviewbot asked some questions:
	https://sashiko.dev/#/patchset/20260320092251.1290207-1-donettom@xxxxxxxxxxxxx