On 03/31/2016 11:58 PM, Richard Weinberger wrote:
During page migrations UBIFS gets confused. We triggered this by using CMA on two different targets. It turned out that fallback_migrate_page() is not suitable for UBIFS as it does not copy the PagePrivate flag. UBIFS is using this flag among with PageChecked to account free space. One possible solution is implementing a ->migratepage() function in UBIFS which does more or less the same as fallback_migrate_page() but also copies PagePrivate. I'm not at all sure whether this is they way to go. IMHO either page migration should not happen if ->migratepage() is not implement or fallback_migrate_page() has to work for all filesystems.
Yes, we could document more thoroughly the expectations of fallback_migrate_page() and audit the existing users, but still relying on every new address_space_operations instance to verify them isn't without risk. And I doubt there can be a default fallback that's guaranteed safe for all filesystems.
Comments? Flames? :-) Thanks, //richard [PATCH 1/2] mm: Export migrate_page_move_mapping and [PATCH 2/2] UBIFS: Implement ->migratepage()
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