linux-kernel - Re: [HMM v15 03/16] mm/ZONE_DEVICE/devmem_pages_remove: allow early removal of device memory

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Date:   Fri, 6 Jan 2017 09:58:34 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Jérôme Glisse <jglisse@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        John Hubbard <jhubbard@...dia.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>
Subject: Re: [HMM v15 03/16] mm/ZONE_DEVICE/devmem_pages_remove: allow early
 removal of device memory

On Fri, Jan 6, 2017 at 8:46 AM, Jérôme Glisse <jglisse@...hat.com> wrote:
> Some device driver manage multiple physical devices memory from a single
> fake device driver. In that case the fake device might outlive the real
> device and ZONE_DEVICE and its resource allocated for a real device would
> waste resources in the meantime.
>
> This patch allow early removal of ZONE_DEVICE and associated resource,
> before device driver is tear down.
>
> Signed-off-by: Jérôme Glisse <jglisse@...hat.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Ross Zwisler <ross.zwisler@...ux.intel.com>
> ---
>  include/linux/memremap.h |  7 +++++++
>  kernel/memremap.c        | 14 ++++++++++++++
>  2 files changed, 21 insertions(+)
>
> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
> index f7e0609..32314d2 100644
> --- a/include/linux/memremap.h
> +++ b/include/linux/memremap.h
> @@ -53,6 +53,7 @@ struct dev_pagemap {
>  void *devm_memremap_pages(struct device *dev, struct resource *res,
>                 struct percpu_ref *ref, struct vmem_altmap *altmap);
>  struct dev_pagemap *find_dev_pagemap(resource_size_t phys);
> +int devm_memremap_pages_remove(struct device *dev, struct dev_pagemap *pgmap);
>
>  static inline bool dev_page_allow_migrate(const struct page *page)
>  {
> @@ -78,6 +79,12 @@ static inline struct dev_pagemap *find_dev_pagemap(resource_size_t phys)
>         return NULL;
>  }
>
> +static inline int devm_memremap_pages_remove(struct device *dev,
> +                                            struct dev_pagemap *pgmap)
> +{
> +       return -EINVAL;
> +}
> +
>  static inline bool dev_page_allow_migrate(const struct page *page)
>  {
>         return false;
> diff --git a/kernel/memremap.c b/kernel/memremap.c
> index 07665eb..250ef25 100644
> --- a/kernel/memremap.c
> +++ b/kernel/memremap.c
> @@ -387,6 +387,20 @@ void *devm_memremap_pages(struct device *dev, struct resource *res,
>  }
>  EXPORT_SYMBOL(devm_memremap_pages);
>
> +static int devm_page_map_match(struct device *dev, void *data, void *match_data)
> +{
> +       struct page_map *page_map = data;
> +
> +       return &page_map->pgmap == match_data;
> +}
> +
> +int devm_memremap_pages_remove(struct device *dev, struct dev_pagemap *pgmap)
> +{
> +       return devres_release(dev, &devm_memremap_pages_release,
> +                             &devm_page_map_match, pgmap);
> +}
> +EXPORT_SYMBOL(devm_memremap_pages_remove);

I think this should be called devm_memunmap_pages() to mirror
devm_memunmap(), and it should take the virtual address returned from
devm_memremap_pages() not pgmap which is an internal detail.