Re: [RFC PATCH v0 0/2] Batch migration for NUMA balancing

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

On 26-May-25 2:16 PM, Huang, Ying wrote:
> Hi, Bharata,
> 
> Bharata B Rao <bharata@amd.com> writes:
> 
>> Hi,
>>
>> This is an attempt to convert the NUMA balancing to do batched
>> migration instead of migrating one folio at a time. The basic
>> idea is to collect (from hint fault handler) the folios to be
>> migrated in a list and batch-migrate them from task_work context.
>> More details about the specifics are present in patch 2/2.
>>
>> During LSFMM[1] and subsequent discussions in MM alignment calls[2],
>> it was suggested that separate migration threads to handle migration
>> or promotion request may be desirable. Existing NUMA balancing, hot
>> page promotion and other future promotion techniques could off-load
>> migration part to these threads.
> 
> What is the expected benefit of the change?

Initially it is about cleanliness and separation of migration into its 
own thread/sub-system.

> 
> For code reuse, we can use migrate_misplaced_folio() or
> migrate_misplaced_folio_batch() in various promotion path.

That's what I have done in this patchset at least. We thought we could 
go full length and off-load migration to its own thread.

> 
> For workload latency influence, per my understanding, PTE scanning is
> much more serious than migration.  Why not start from that?

Raghu's PTE A bit scanning is one effort towards that (Removing PTE 
scanning from task context.

Regards,
Bharata.