Re: [RFC PATCH v0 2/2] mm: sched: Batch-migrate misplaced pages

[Bharata B Rao <bharata@amd.com>]

On 22-May-25 9:41 PM, David Hildenbrand wrote:
> On 21.05.25 10:02, Bharata B Rao wrote:
>> Currently the folios identified as misplaced by the NUMA
>> balancing sub-system are migrated one by one from the NUMA
>> hint fault handler as and when they are identified as
>> misplaced.
>>
>> Instead of such singe folio migrations, batch them and
>> migrate them at once.
>>
>> Identified misplaced folios are isolated and stored in
>> a per-task list. A new task_work is queued from task tick
>> handler to migrate them in batches. Migration is done
>> periodically or if pending number of isolated foios exceeds
>> a threshold.
> 
> That means that these pages are effectively unmovable for other purposes 
> (CMA, compaction, long-term pinning, whatever) until that list was drained.
> 
> Bad.

During the last week's MM alignment call on this subject, it was decided 
not to isolate and batch from fault context and migrate from task_work 
context like this.

However since the amount of time the folios stay in isolated state was
bounded both by time(1s in my patchset) and the number of folios 
isolated, I thought it should be okay, but I may be wrong.

Regards,
Bharata.