On Mon, May 22, 2017 at 9:51 AM, Jérôme Glisse <jglisse@xxxxxxxxxx> wrote:
> A ZONE_DEVICE page that reach a refcount of 1 is free ie no longer
> have any user. For device private pages this is important to catch
> and thus we need to special case put_page() for this.
>
> Signed-off-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> ---
> include/linux/mm.h | 30 ++++++++++++++++++++++++++++++
> kernel/memremap.c | 1 -
> 2 files changed, 30 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index a825dab..11f7bac 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -23,6 +23,7 @@
> #include <linux/page_ext.h>
> #include <linux/err.h>
> #include <linux/page_ref.h>
> +#include <linux/memremap.h>
>
> struct mempolicy;
> struct anon_vma;
> @@ -795,6 +796,20 @@ static inline bool is_device_private_page(const struct page *page)
> return ((page_zonenum(page) == ZONE_DEVICE) &&
> (page->pgmap->type == MEMORY_DEVICE_PRIVATE));
> }
> +
> +static inline void put_zone_device_private_page(struct page *page)
> +{
> + int count = page_ref_dec_return(page);
> +
> + /*
> + * If refcount is 1 then page is freed and refcount is stable as nobody
> + * holds a reference on the page.
> + */
> + if (count == 1)
> + page->pgmap->page_free(page, page->pgmap->data);
> + else if (!count)
> + __put_page(page);
> +}
> #else
> static inline bool is_zone_device_page(const struct page *page)
> {
> @@ -805,6 +820,10 @@ static inline bool is_device_private_page(const struct page *page)
> {
> return false;
> }
> +
> +static inline void put_zone_device_private_page(struct page *page)
> +{
> +}
> #endif
>
> static inline void get_page(struct page *page)
> @@ -822,6 +841,17 @@ static inline void put_page(struct page *page)
> {
> page = compound_head(page);
>
> + /*
> + * For private device pages we need to catch refcount transition from
> + * 2 to 1, when refcount reach one it means the private device page is
> + * free and we need to inform the device driver through callback. See
> + * include/linux/memremap.h and HMM for details.
> + */
> + if (unlikely(is_device_private_page(page))) {
Since I presume HMM is a niche use case can we make this a
"static_branch_unlikely(&hmm_key) && is_device_private_page(page))"?
That way non-hmm platforms see minimal overhead.
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href
