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fsdax: improve the FS_DAX Kconfig description and help text

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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>
Link: https://lore.kernel.org/r/20210826135510.6293-2-hch@lst.de
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
This commit is contained in:
Christoph Hellwig 2021-08-26 15:55:02 +02:00 committed by Dan Williams
parent 7c60610d47
commit 6c97ec172a
1 changed files with 18 additions and 3 deletions
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21
fs/Kconfig
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@ -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