[PATCH] dax : Fix documentation with respect to struct pages

[PATCH] dax : Fix documentation with respect to struct pages

[Stephen Bates]

The documentation for dax is not up to date with respect to the struct
page support available in some of the device drivers that utilize
it.

Signed-off-by: Stephen Bates <sbates@raithlin.com>
---
 Documentation/filesystems/dax.txt | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/Documentation/filesystems/dax.txt b/Documentation/filesystems/dax.txt
index 0c16a22..23d18b8 100644
--- a/Documentation/filesystems/dax.txt
+++ b/Documentation/filesystems/dax.txt
@@ -123,9 +123,12 @@ The DAX code does not work correctly on architectures which have virtually
 mapped caches such as ARM, MIPS and SPARC.
 
 Calling get_user_pages() on a range of user memory that has been mmaped
-from a DAX file will fail as there are no 'struct page' to describe
-those pages.  This problem is being worked on.  That means that O_DIRECT
-reads/writes to those memory ranges from a non-DAX file will fail (note
-that O_DIRECT reads/writes _of a DAX file_ do work, it is the memory
-that is being accessed that is key here).  Other things that will not
-work include RDMA, sendfile() and splice().
+from a DAX file will fail when there are no 'struct page' to describe
+those pages.  This problem has been addressed in some device drivers
+by adding optional struct page support for pages under the control of
+the driver (see CONFIG_NVDIMM_PFN in drivers/nvdimm for an example of
+how to do this). In the non struct page cases O_DIRECT reads/writes to
+those memory ranges from a non-DAX file will fail (note that O_DIRECT
+reads/writes _of a DAX file_ do work, it is the memory that is being
+accessed that is key here).  Other things that will not work in the
+non struct page case include RDMA, sendfile() and splice().
-- 
2.5.0

Re: [PATCH] dax : Fix documentation with respect to struct pages

[Ross Zwisler]

On Sun, Sep 25, 2016 at 07:18:37PM -0600, Stephen Bates wrote:
> The documentation for dax is not up to date with respect to the struct
> page support available in some of the device drivers that utilize
> it.
> 
> Signed-off-by: Stephen Bates <sbates@raithlin.com>

Great, thanks for updating this.

Acked-by: Ross Zwisler <ross.zwisler@linux.intel.com>

> ---
>  Documentation/filesystems/dax.txt | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/Documentation/filesystems/dax.txt b/Documentation/filesystems/dax.txt
> index 0c16a22..23d18b8 100644
> --- a/Documentation/filesystems/dax.txt
> +++ b/Documentation/filesystems/dax.txt
> @@ -123,9 +123,12 @@ The DAX code does not work correctly on architectures which have virtually
>  mapped caches such as ARM, MIPS and SPARC.
>  
>  Calling get_user_pages() on a range of user memory that has been mmaped
> -from a DAX file will fail as there are no 'struct page' to describe
> -those pages.  This problem is being worked on.  That means that O_DIRECT
> -reads/writes to those memory ranges from a non-DAX file will fail (note
> -that O_DIRECT reads/writes _of a DAX file_ do work, it is the memory
> -that is being accessed that is key here).  Other things that will not
> -work include RDMA, sendfile() and splice().
> +from a DAX file will fail when there are no 'struct page' to describe
> +those pages.  This problem has been addressed in some device drivers
> +by adding optional struct page support for pages under the control of
> +the driver (see CONFIG_NVDIMM_PFN in drivers/nvdimm for an example of
> +how to do this). In the non struct page cases O_DIRECT reads/writes to
> +those memory ranges from a non-DAX file will fail (note that O_DIRECT
> +reads/writes _of a DAX file_ do work, it is the memory that is being
> +accessed that is key here).  Other things that will not work in the
> +non struct page case include RDMA, sendfile() and splice().
> -- 
> 2.5.0
> 

Re: [PATCH] dax : Fix documentation with respect to struct pages

[Jonathan Corbet]

On Tue, 27 Sep 2016 10:52:48 -0600
Ross Zwisler <ross.zwisler@linux.intel.com> wrote:

> On Sun, Sep 25, 2016 at 07:18:37PM -0600, Stephen Bates wrote:
> > The documentation for dax is not up to date with respect to the struct
> > page support available in some of the device drivers that utilize
> > it.
> > 
> > Signed-off-by: Stephen Bates <sbates@raithlin.com>  
> 
> Great, thanks for updating this.
> 
> Acked-by: Ross Zwisler <ross.zwisler@linux.intel.com>

Applied to the docs tree, thanks.

jon