@@ -43,7 +43,7 @@ source "fs/f2fs/Kconfig"
source "fs/zonefs/Kconfig"
config FS_DAX
- bool "Direct Access (DAX) support"
+ bool "File system based Direct Access (DAX) support"
depends on MMU
depends on !(ARM || MIPS || SPARC)
select DEV_PAGEMAP_OPS if (ZONE_DEVICE && !FS_DAX_LIMITED)
@@ -53,8 +53,23 @@ config FS_DAX
Direct Access (DAX) can be used on memory-backed block devices.
If the block device supports DAX and the filesystem supports DAX,
then you can avoid using the pagecache to buffer I/Os. Turning
- on this option will compile in support for DAX; you will need to
- mount the filesystem using the -o dax option.
+ on this option will compile in support for DAX.
+
+ For a DAX device to support file system access it needs to have
+ struct pages. For the nfit based NVDIMMs this can be enabled
+ using the ndctl utility:
+
+ # ndctl create-namespace --force --reconfig=namespace0.0 \
+ --mode=fsdax --map=mem
+
+ See the 'create-namespace' man page for details on the overhead of
+ --map=mem:
+ https://docs.pmem.io/ndctl-user-guide/ndctl-man-pages/ndctl-create-namespace
+
+ For ndctl to work CONFIG_DEV_DAX needs to be enabled as well. For most
+ file systems DAX support needs to be manually enabled globally or
+ per-inode using a mount option as well. See the file documentation in
+ Documentation/filesystems/dax.rst for details.
If you do not have a block device that is capable of using this,
or if unsure, say N. Saying Y will increase the size of the kernel
Rename the main option text to clarify it is for file system access, and add a bit of text that explains how to actually switch a nvdimm to a fsdax capable state. Signed-off-by: Christoph Hellwig <hch@lst.de> --- fs/Kconfig | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-)