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Date:   Wed, 13 Nov 2019 20:24:41 -0500
From:   Jerome Glisse <jglisse@redhat.com>
To:     Dan Williams <dan.j.williams@intel.com>
Cc:     jhubbard@nvidia.com, Jan Kara <jack@suse.cz>,
        Christoph Hellwig <hch@lst.de>,
        Ira Weiny <ira.weiny@intel.com>, linux-nvdimm@lists.01.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] mm: Cleanup __put_devmap_managed_page() vs ->page_free()
Message-ID: <20191114012441.GA6395@redhat.com>
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On Wed, Nov 13, 2019 at 04:07:22PM -0800, Dan Williams wrote:
> After the removal of the device-public infrastructure there are only 2
> ->page_free() call backs in the kernel. One of those is a device-private
> callback in the nouveau driver, the other is a generic wakeup needed in
> the DAX case. In the hopes that all ->page_free() callbacks can be
> migrated to common core kernel functionality, move the device-private
> specific actions in __put_devmap_managed_page() under the
> is_device_private_page() conditional, including the ->page_free()
> callback. For the other page types just open-code the generic wakeup.
>=20
> Yes, the wakeup is only needed in the MEMORY_DEVICE_FSDAX case, but it
> does no harm in the MEMORY_DEVICE_DEVDAX and MEMORY_DEVICE_PCI_P2PDMA
> case.
>=20
> Cc: Jan Kara <jack@suse.cz>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Ira Weiny <ira.weiny@intel.com>
> Cc: J=E9r=F4me Glisse <jglisse@redhat.com>
> Cc: John Hubbard <jhubbard@nvidia.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

All looks good to me.

Reviewed-by: J=E9r=F4me Glisse <jglisse@redhat.com>


> ---
> Hi John,
>=20
> This applies on top of today's linux-next and passes my nvdimm unit
> tests. That testing noticed that devmap_managed_enable_get() needed a
> small fixup as well.
>=20
>  drivers/nvdimm/pmem.c |    6 ------
>  mm/memremap.c         |   22 ++++++++++++----------
>  2 files changed, 12 insertions(+), 16 deletions(-)
>=20
> diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> index f9f76f6ba07b..21db1ce8c0ae 100644
> --- a/drivers/nvdimm/pmem.c
> +++ b/drivers/nvdimm/pmem.c
> @@ -338,13 +338,7 @@ static void pmem_release_disk(void *__pmem)
>  =09put_disk(pmem->disk);
>  }
> =20
> -static void pmem_pagemap_page_free(struct page *page)
> -{
> -=09wake_up_var(&page->_refcount);
> -}
> -
>  static const struct dev_pagemap_ops fsdax_pagemap_ops =3D {
> -=09.page_free=09=09=3D pmem_pagemap_page_free,
>  =09.kill=09=09=09=3D pmem_pagemap_kill,
>  =09.cleanup=09=09=3D pmem_pagemap_cleanup,
>  };
> diff --git a/mm/memremap.c b/mm/memremap.c
> index 022e78e68ea0..6e6f3d6fdb73 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -27,7 +27,8 @@ static void devmap_managed_enable_put(void)
> =20
>  static int devmap_managed_enable_get(struct dev_pagemap *pgmap)
>  {
> -=09if (!pgmap->ops || !pgmap->ops->page_free) {
> +=09if (!pgmap->ops || (pgmap->type =3D=3D MEMORY_DEVICE_PRIVATE
> +=09=09=09=09&& !pgmap->ops->page_free)) {
>  =09=09WARN(1, "Missing page_free method\n");
>  =09=09return -EINVAL;
>  =09}
> @@ -449,12 +450,6 @@ void __put_devmap_managed_page(struct page *page)
>  =09 * holds a reference on the page.
>  =09 */
>  =09if (count =3D=3D 1) {
> -=09=09/* Clear Active bit in case of parallel mark_page_accessed */
> -=09=09__ClearPageActive(page);
> -=09=09__ClearPageWaiters(page);
> -
> -=09=09mem_cgroup_uncharge(page);
> -
>  =09=09/*
>  =09=09 * When a device_private page is freed, the page->mapping field
>  =09=09 * may still contain a (stale) mapping value. For example, the
> @@ -476,10 +471,17 @@ void __put_devmap_managed_page(struct page *page)
>  =09=09 * handled differently or not done at all, so there is no need
>  =09=09 * to clear page->mapping.
>  =09=09 */
> -=09=09if (is_device_private_page(page))
> -=09=09=09page->mapping =3D NULL;
> +=09=09if (is_device_private_page(page)) {
> +=09=09=09/* Clear Active bit in case of parallel mark_page_accessed */
> +=09=09=09__ClearPageActive(page);
> +=09=09=09__ClearPageWaiters(page);
> =20
> -=09=09page->pgmap->ops->page_free(page);
> +=09=09=09mem_cgroup_uncharge(page);
> +
> +=09=09=09page->mapping =3D NULL;
> +=09=09=09page->pgmap->ops->page_free(page);
> +=09=09} else
> +=09=09=09wake_up_var(&page->_refcount);
>  =09} else if (!count)
>  =09=09__put_page(page);
>  }
>=20