[PATCH 7/8] mm: remove the extra ZONE_DEVICE struct page refcount

[Ralph Campbell]

On 2/6/22 22:32, Christoph Hellwig wrote:
> ZONE_DEVICE struct pages have an extra reference count that complicates
> the code for put_page() and several places in the kernel that need to
> check the reference count to see that a page is not being used (gup,
> compaction, migration, etc.). Clean up the code so the reference count
> doesn't need to be treated specially for ZONE_DEVICE pages.
>
> Note that this excludes the special idle page wakeup for fsdax pages,
> which still happens at refcount 1.  This is a separate issue and will
> be sorted out later.  Given that only fsdax pages require the
> notifiacation when the refcount hits 1 now, the PAGEMAP_OPS Kconfig
> symbol can go away and be replaced with a FS_DAX check for this hook
> in the put_page fastpath.
>
> Based on an earlier patch from Ralph Campbell <rcampbell at nvidia.com>.
>
> Signed-off-by: Christoph Hellwig <hch at lst.de>

Thanks for working on this, definite step forward.

Reviewed-by: Ralph Campbell <rcampbell at nvidia.com>