Re: [PATCH 2/2] mm: remove extra ZONE_DEVICE struct page refcount

[Bharata B Rao]

On Fri, Sep 25, 2020 at 01:44:42PM -0700, Ralph Campbell 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.
> 
> Signed-off-by: Ralph Campbell <rcampbell@xxxxxxxxxx>
> ---
>  arch/powerpc/kvm/book3s_hv_uvmem.c     |  2 +-
>  drivers/gpu/drm/nouveau/nouveau_dmem.c |  2 +-
>  include/linux/dax.h                    |  2 +-
>  include/linux/memremap.h               |  7 ++-
>  include/linux/mm.h                     | 44 --------------
>  lib/test_hmm.c                         |  2 +-
>  mm/gup.c                               | 44 --------------
>  mm/internal.h                          |  8 +++
>  mm/memremap.c                          | 82 ++++++--------------------
>  mm/migrate.c                           |  5 --
>  mm/page_alloc.c                        |  3 +
>  mm/swap.c                              | 46 +++------------
>  12 files changed, 44 insertions(+), 203 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
> index 7705d5557239..e6ec98325fab 100644
> --- a/arch/powerpc/kvm/book3s_hv_uvmem.c
> +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
> @@ -711,7 +711,7 @@ static struct page *kvmppc_uvmem_get_page(unsigned long gpa, struct kvm *kvm)
>  
>  	dpage = pfn_to_page(uvmem_pfn);
>  	dpage->zone_device_data = pvt;
> -	get_page(dpage);
> +	init_page_count(dpage);

The powerpc change looks good. Passes a quick sanity test of
booting/rebooting a secure guest on Power.

Tested-by: Bharata B Rao <bharata@xxxxxxxxxxxxx>

Regards,
Bharata.