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

From: Bharata B Rao <bharata@linux.ibm.com>
To: Ralph Campbell <rcampbell@nvidia.com>
Cc: linux-mm@kvack.org, kvm-ppc@vger.kernel.org,
	nouveau@lists.freedesktop.org, linux-kernel@vger.kernel.org,
	Dan Williams <dan.j.williams@intel.com>,
	Ira Weiny <ira.weiny@intel.com>,
	Matthew Wilcox <willy@infradead.org>,
	Jerome Glisse <jglisse@redhat.com>,
	John Hubbard <jhubbard@nvidia.com>,
	Alistair Popple <apopple@nvidia.com>,
	Christoph Hellwig <hch@lst.de>, Jason Gunthorpe <jgg@nvidia.com>,
	Zi Yan <ziy@nvidia.com>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	Yang Shi <yang.shi@linux.alibaba.com>,
	Paul Mackerras <paulus@ozlabs.org>,
	Ben Skeggs <bskeggs@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 2/2] mm: remove extra ZONE_DEVICE struct page refcount
Date: Tue, 29 Sep 2020 08:29:41 +0530	[thread overview]
Message-ID: <20200929025941.GA257792@in.ibm.com> (raw)
In-Reply-To: <20200925204442.31348-3-rcampbell@nvidia.com>

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@nvidia.com>
> ---
>  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@linux.ibm.com>

Regards,
Bharata.