Re: [RFC PATCH 0/2] mm/migrate: wait for folio refcount during longterm pin migration

Huang, Ying
2026-04-22T01:46:37Z

"David Hildenbrand (Arm)" <david@kernel.org> writes:

> On 4/21/26 11:19, Huang, Ying wrote:
>> Hi, John,
>>
>> John Hubbard <jhubbard@nvidia.com> writes:
>>
>>> Hi,
>>>
>>> This adds a bounded sleep to migration so that FOLL_LONGTERM pinning can
>>> wait for transient folio references to drain, instead of failing after a
>>> fixed number of retries. The wait uses a one-second timeout. An
>>
>> Is the one-second timeout appropriate for all users? Do some users
>> prefer fail-fast behavior instead? If so, should we add another FOLL
>> flag to support a timed wait?
>
> We should avoid a FOLL flag to affect that behavior. FOLL_LONGTERM
> already implies that things could take a while.

Yes. I am just not sure whether one-second is OK for all users.

> So we have real examples were failing is even desirable? :)

Hi, John,

Could you do some research on this?

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Best Regards,
Huang, Ying