On Wed, Feb 14, 2024 at 12:04:10PM +0530, Charan Teja Kalla wrote:
- 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.
I think you have a misunderstanding. David's patch cfeed8ffe55b (part of 6.6) _stopped_ us using the tail ->private entries. So in 6.1, these tail pages should already have page->private set, and I don't understand what you're fixing.
- 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@infradead.org 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.