Re: [PATCH v4 21/23] mm: use custom page_free for P2PDMA pages

[Logan Gunthorpe]

On 2021-12-21 2:06 a.m., Christoph Hellwig wrote:
> On Wed, Nov 17, 2021 at 02:54:08PM -0700, Logan Gunthorpe wrote:
>> When P2PDMA pages are passed to userspace, they will need to be
>> reference counted properly and returned to their genalloc after their
>> reference count returns to 1. This is accomplished with the existing
>> DEV_PAGEMAP_OPS and the .page_free() operation.
>>
>> Change CONFIG_P2PDMA to select CONFIG_DEV_PAGEMAP_OPS and add
>> MEMORY_DEVICE_PCI_P2PDMA to page_is_devmap_managed(),
>> devmap_managed_enable_[put|get]() and free_devmap_managed_page().
> 
> Uuuh.  We are trying hard to kill off this magic free at refcount 1
> behavior in the amdgpu device coherent series.  We really should not
> add more of this.

Ah, ok. I found Ralph's patch that cleans this up and I can try to
rebase this onto it for future postings until it gets merged.

Your other comments I can address for the next time I post this series.

Thanks for the review!

Logan