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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" source "fs/zonefs/Kconfig"
config FS_DAX config FS_DAX
bool "Direct Access (DAX) support" bool "File system based Direct Access (DAX) support"
depends on MMU depends on MMU
depends on !(ARM || MIPS || SPARC) depends on !(ARM || MIPS || SPARC)
select DEV_PAGEMAP_OPS if (ZONE_DEVICE && !FS_DAX_LIMITED) 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. Direct Access (DAX) can be used on memory-backed block devices.
If the block device supports DAX and the filesystem supports DAX, If the block device supports DAX and the filesystem supports DAX,
then you can avoid using the pagecache to buffer I/Os. Turning 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 on this option will compile in support for DAX.
mount the filesystem using the -o dax option.
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, 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 or if unsure, say N. Saying Y will increase the size of the kernel