Re: [RFC PATCH v4 4/6] mm/migrate: add copy offload registration infrastructure

Garg, Shivank
2026-03-10T10:08:09Z

On 3/9/2026 11:24 PM, Gregory Price wrote:
> On Mon, Mar 09, 2026 at 12:07:29PM +0000, Shivank Garg wrote:
> ... snip ...
>>
>> Only one migrator can be active a time. A second registration returns
>> -EBUSY, and only the active migrator can stop itself. The static_call
>> dispatch is under SRCU so synchronize_srcu() in stop path guarantees
>> no in-flight copy before the module reference is dropped.
>>
> ... snip ...
>
>> @@ -1820,11 +1833,18 @@ static int migrate_pages_batch(struct list_head *from,
>>
>> +#ifdef CONFIG_MIGRATION_COPY_OFFLOAD
>> + /* Check if the offload driver wants to batch for this reason */
>> + if (static_branch_unlikely(&migrate_offload_enabled))
>> + do_batch = static_call(migrate_should_batch)(reason);
>> +#endif
>> +
>
> should the migrate_should_batch call also be done under srcu?
>
> In theory it's an incredibly small window, but there is a race window.

Yes, right.
thanks for pointing this out.

Best regards,
Shivank