Longterm pinning of FS DAX pages should already be disallowed by
various pXX_devmap checks. However a future change will cause these
checks to be invalid for FS DAX pages so make
folio_is_longterm_pinnable() return false for FS DAX pages.

Signed-off-by: Alistair Popple <apopple@nvidia.com>
---
 include/linux/memremap.h | 11 +++++++++++
 include/linux/mm.h       |  4 ++++
 2 files changed, 15 insertions(+)

diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index 14273e6..6a1406a 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -187,6 +187,17 @@ static inline bool folio_is_device_coherent(const struct folio *folio)
 	return is_device_coherent_page(&folio->page);
 }
 
+static inline bool is_device_dax_page(const struct page *page)
+{
+	return is_zone_device_page(page) &&
+		page_dev_pagemap(page)->type == MEMORY_DEVICE_FS_DAX;
+}
+
+static inline bool folio_is_device_dax(const struct folio *folio)
+{
+	return is_device_dax_page(&folio->page);
+}
+
 #ifdef CONFIG_ZONE_DEVICE
 void zone_device_page_init(struct page *page);
 void *memremap_pages(struct dev_pagemap *pgmap, int nid);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index ae6d713..935e493 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1989,6 +1989,10 @@ static inline bool folio_is_longterm_pinnable(struct folio *folio)
 	if (folio_is_device_coherent(folio))
 		return false;
 
+	/* DAX must also always allow eviction. */
+	if (folio_is_device_dax(folio))
+		return false;
+
 	/* Otherwise, non-movable zone folios can be pinned. */
 	return !folio_is_zone_movable(folio);
 
-- 
git-series 0.9.1

Alistair Popple wrote:
> Longterm pinning of FS DAX pages should already be disallowed by
> various pXX_devmap checks. However a future change will cause these
> checks to be invalid for FS DAX pages so make
> folio_is_longterm_pinnable() return false for FS DAX pages.
> 
> Signed-off-by: Alistair Popple <apopple@nvidia.com>
> ---
>  include/linux/memremap.h | 11 +++++++++++
>  include/linux/mm.h       |  4 ++++
>  2 files changed, 15 insertions(+)
> 
> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
> index 14273e6..6a1406a 100644
> --- a/include/linux/memremap.h
> +++ b/include/linux/memremap.h
> @@ -187,6 +187,17 @@ static inline bool folio_is_device_coherent(const struct folio *folio)
>  	return is_device_coherent_page(&folio->page);
>  }
>  
> +static inline bool is_device_dax_page(const struct page *page)
> +{
> +	return is_zone_device_page(page) &&
> +		page_dev_pagemap(page)->type == MEMORY_DEVICE_FS_DAX;
> +}
> +
> +static inline bool folio_is_device_dax(const struct folio *folio)
> +{
> +	return is_device_dax_page(&folio->page);
> +}
> +
>  #ifdef CONFIG_ZONE_DEVICE
>  void zone_device_page_init(struct page *page);
>  void *memremap_pages(struct dev_pagemap *pgmap, int nid);
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index ae6d713..935e493 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1989,6 +1989,10 @@ static inline bool folio_is_longterm_pinnable(struct folio *folio)
>  	if (folio_is_device_coherent(folio))
>  		return false;
>  
> +	/* DAX must also always allow eviction. */
> +	if (folio_is_device_dax(folio))

Why is this called "folio_is_device_dax()" when the check is for fsdax?

I would expect:

if (folio_is_fsdax(folio))
	return false;

...and s/device_dax/fsdax/ for the rest of the helpers.

Dan Williams wrote:
> Alistair Popple wrote:
> > Longterm pinning of FS DAX pages should already be disallowed by
> > various pXX_devmap checks. However a future change will cause these
> > checks to be invalid for FS DAX pages so make
> > folio_is_longterm_pinnable() return false for FS DAX pages.
> > 
> > Signed-off-by: Alistair Popple <apopple@nvidia.com>
> > ---
> >  include/linux/memremap.h | 11 +++++++++++
> >  include/linux/mm.h       |  4 ++++
> >  2 files changed, 15 insertions(+)
> > 
> > diff --git a/include/linux/memremap.h b/include/linux/memremap.h
> > index 14273e6..6a1406a 100644
> > --- a/include/linux/memremap.h
> > +++ b/include/linux/memremap.h
> > @@ -187,6 +187,17 @@ static inline bool folio_is_device_coherent(const struct folio *folio)
> >  	return is_device_coherent_page(&folio->page);
> >  }
> >  
> > +static inline bool is_device_dax_page(const struct page *page)
> > +{
> > +	return is_zone_device_page(page) &&
> > +		page_dev_pagemap(page)->type == MEMORY_DEVICE_FS_DAX;
> > +}
> > +
> > +static inline bool folio_is_device_dax(const struct folio *folio)
> > +{
> > +	return is_device_dax_page(&folio->page);
> > +}
> > +
> >  #ifdef CONFIG_ZONE_DEVICE
> >  void zone_device_page_init(struct page *page);
> >  void *memremap_pages(struct dev_pagemap *pgmap, int nid);
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index ae6d713..935e493 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -1989,6 +1989,10 @@ static inline bool folio_is_longterm_pinnable(struct folio *folio)
> >  	if (folio_is_device_coherent(folio))
> >  		return false;
> >  
> > +	/* DAX must also always allow eviction. */
> > +	if (folio_is_device_dax(folio))
> 
> Why is this called "folio_is_device_dax()" when the check is for fsdax?
> 
> I would expect:
> 
> if (folio_is_fsdax(folio))
> 	return false;
> 
> ...and s/device_dax/fsdax/ for the rest of the helpers.

Specifically devdax is ok to allow longterm pinning since it is
statically allocated. fsdax is the only ZONE_DEVICE mode where there is
a higher-level allocator that does not support a 3rd party the block its
operations indefinitely with a pin. So this needs to be explicit for
that case.

Dan Williams <dan.j.williams@intel.com> writes:

> Dan Williams wrote:
>> Alistair Popple wrote:
>> > Longterm pinning of FS DAX pages should already be disallowed by
>> > various pXX_devmap checks. However a future change will cause these
>> > checks to be invalid for FS DAX pages so make
>> > folio_is_longterm_pinnable() return false for FS DAX pages.
>> > 
>> > Signed-off-by: Alistair Popple <apopple@nvidia.com>
>> > ---
>> >  include/linux/memremap.h | 11 +++++++++++
>> >  include/linux/mm.h       |  4 ++++
>> >  2 files changed, 15 insertions(+)
>> > 
>> > diff --git a/include/linux/memremap.h b/include/linux/memremap.h
>> > index 14273e6..6a1406a 100644
>> > --- a/include/linux/memremap.h
>> > +++ b/include/linux/memremap.h
>> > @@ -187,6 +187,17 @@ static inline bool folio_is_device_coherent(const struct folio *folio)
>> >  	return is_device_coherent_page(&folio->page);
>> >  }
>> >  
>> > +static inline bool is_device_dax_page(const struct page *page)
>> > +{
>> > +	return is_zone_device_page(page) &&
>> > +		page_dev_pagemap(page)->type == MEMORY_DEVICE_FS_DAX;
>> > +}
>> > +
>> > +static inline bool folio_is_device_dax(const struct folio *folio)
>> > +{
>> > +	return is_device_dax_page(&folio->page);
>> > +}
>> > +
>> >  #ifdef CONFIG_ZONE_DEVICE
>> >  void zone_device_page_init(struct page *page);
>> >  void *memremap_pages(struct dev_pagemap *pgmap, int nid);
>> > diff --git a/include/linux/mm.h b/include/linux/mm.h
>> > index ae6d713..935e493 100644
>> > --- a/include/linux/mm.h
>> > +++ b/include/linux/mm.h
>> > @@ -1989,6 +1989,10 @@ static inline bool folio_is_longterm_pinnable(struct folio *folio)
>> >  	if (folio_is_device_coherent(folio))
>> >  		return false;
>> >  
>> > +	/* DAX must also always allow eviction. */
>> > +	if (folio_is_device_dax(folio))
>> 
>> Why is this called "folio_is_device_dax()" when the check is for fsdax?
>> 
>> I would expect:
>> 
>> if (folio_is_fsdax(folio))
>> 	return false;
>> 
>> ...and s/device_dax/fsdax/ for the rest of the helpers.
>
> Specifically devdax is ok to allow longterm pinning since it is
> statically allocated. fsdax is the only ZONE_DEVICE mode where there is
> a higher-level allocator that does not support a 3rd party the block its
> operations indefinitely with a pin. So this needs to be explicit for
> that case.

Yeah, that all makes sense. I see what I did - was thinking in terms of
is this a zone device page - is_device - and if so what type
_(fs)dax. folio_is_fsdax() is much clearer though, thanks!