Thanks David.
On 2/14/2024 12:06 AM, David Hildenbrand wrote:
>>>
>>> Isn't there a way to bite the bullet and backport that series to 6.1
>>> instead?
>>
>> My worry is that, because of merge conflicts, not sure If It can end up
>> in inducing some other issues.
>
> I can have a look this/next week. I don't recall if there was any
> particular dependency.
>
That would help me...
>>
>> Although we didn't test THP on older kernels, from the code walk, it
>> seems issue persists to me on older to 6.1 kernel, unless I am missing
>> something here. So back porting of this series to all those LTS kernels,
>> may not be a straight forward?
>>
>> So, I am really not sure of what is the way forward here...
>
> Again, if we want to fix this properly, we should first identify the
> commit that actually broke it.
>
> If it predates folios, we'd need different fixes for different stable
> kernels most likely.
>
> The big question are:
>
> 1) Is it broken in 5.15? Did you actually try to reproduce or is this
> just a guess?
>
We didn't run the tests with THP enabled on 5.15, __so we didn't
encounter this issue__ on older to 6.1 kernels.
I mentioned that issue exists is based on my understanding after code
walk through. To be specific, I just looked to the
migrate_pages()->..->migrate_page_move_mapping() &
__split_huge_page_tail() where the ->private field of thp sub-pages is
not filled with swap entry. If it could have set, I think these are the
only places where it would have done, per my understanding. CMIW.
> 2) How did you come up with 417013e0d18 ("mm/migrate: Add
> folio_migrate_mapping()")
OOPS, I mean it is Fixes: 3417013e0d18 ("mm/migrate: Add
folio_migrate_mapping()").
My understanding is that it a miss in folio_migrate_mapping() where the
sub-pages should've the ->private set. But this is just a
reimplementation of migrate_page_move_mapping()(where also the issue
exists, tmk).
commit 3417013e0d183be9b42d794082eec0ec1c5b5f15
Author: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Date: Fri May 7 07:28:40 2021 -0400
mm/migrate: Add folio_migrate_mapping()
Reimplement migrate_page_move_mapping() as a wrapper around
folio_migrate_mapping(). Saves 193 bytes of kernel text.
Thanks.
