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dax : Fix documentation with respect to struct pages 

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>
Acked-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Stephen Bates 2016-09-25 19:18:37 -06:00 committed by Jonathan Corbet
parent 964cce16b1
commit 9ff2dc5601
1 changed files with 9 additions and 6 deletions
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15
Documentation/filesystems/dax.txt
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@ -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().