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

[David Hildenbrand <david@redhat.com>]

On 22.05.25 18:24, Zi Yan wrote:
> On 22 May 2025, at 12:11, 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.
> 
> Probably we can mark these pages and when others want to migrate the page,
> get_new_page() just looks at the page's target node and get a new page from
> the target node.

How do you envision that working when CMA needs to migrate this exact 
page to a different location?

It cannot isolate it for migration because ... it's already isolated ... 
so it will give up.

Marking might not be easy I assume ...

-- 
Cheers,

David / dhildenb