Re: [PATCH v6 1/2] mm: migration: fix the FOLL_GET failure on following huge page

[Michael Ellerman]

Mike Kravetz <mike.kravetz@xxxxxxxxxx> writes:
> On 08/16/22 22:43, Andrew Morton wrote:
>> On Wed, 17 Aug 2022 03:31:37 +0000 "Wang, Haiyue" <haiyue.wang@xxxxxxxxx> wrote:
>>
>> > > >  		}
>> > >
>> > > I would be better to fix this for real at those three client code sites?
>> >
>> > Then 5.19 will break for a while to wait for the final BIG patch ?
>>
>> If that's the proposal then your [1/2] should have had a cc:stable and
>> changelog words describing the plan for 6.0.
>>
>> But before we do that I'd like to see at least a prototype of the final
>> fixes to s390 and hugetlb, so we can assess those as preferable for
>> backporting.  I don't think they'll be terribly intrusive or risky?
>
> I will start on adding follow_huge_pgd() support.  Although, I may need
> some help with verification from the powerpc folks, as that is the only
> architecture which supports hugetlb pages at that level.
>
> mpe any suggestions?

I'm happy to test.

I have a system where I can allocate 1GB huge pages.

I'm not sure how to actually test this path though. I hacked up the
vm/migration.c test to allocate 1GB hugepages, but I can't see it going
through follow_huge_pgd() (using ftrace).

Maybe I hacked it up badly, I'll have a closer look on Monday. But if
you have any tips on how to trigger that path let me know :)

cheers