On Tue, Jun 17, 2025 at 11:44:30AM +0200, David Hildenbrand wrote: > On 16.06.25 13:58, Alistair Popple wrote: > > The only users of pmd_devmap were device dax and fs dax. The check for > > pmd_devmap() in check_pmd_state() is therefore redundant as callers > > explicitly check for is_zone_device_page(), so this check can be dropped. > > > > Looking again, is this true? > > If we return "SCAN_SUCCEED", we assume there is a page table there that we > can map and walk. > > But I assume we can drop that check because nobody will ever set > pmd_devmap() anymore? > > So likely just the description+sibject of this patch should be adjusted.
Ugh. I wish I had've documented this better because it's all very "obvious", but I think the description is still accurate. These devmap checks could never have been hit and were therefore redundant, because in practice all callers call thp_vma_allowable_order() either before or after check_pmd_state() (or both). thp_vma_allowable_order() will eventually (in __thp_vma_allowable_orders()) check for a DAX VMA and bail. But yes, I should call that out in the patch subject so I don't have to keep relearning this obvious fact :-) > FWIW, I think check_pmd_state() should be changed to work on pmd_leaf() etc, > but that's something for another day. Sure, and I do appreciate these kind of remarks because sometimes I get bored enough to come back and actually do them. Not very often ... but sometimes. > -- > Cheers, > > David / dhildenb >
