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authorChristoph Hellwig <hch@lst.de>2021-08-26 15:55:02 +0200
committerDan Williams <dan.j.williams@intel.com>2021-08-26 16:52:02 -0700
commit6c97ec172a1c058a66e7c79308a0d7f11753865d (patch)
treef50db1aea60a5068ca8e1c896018a87fc75be0cc /fs
parent7c60610d476766e128cc4284bb6349732cbd6606 (diff)
fsdax: improve the FS_DAX Kconfig description and help text
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>
Diffstat (limited to 'fs')
-rw-r--r--fs/Kconfig21
1 files changed, 18 insertions, 3 deletions
diff --git a/fs/Kconfig b/fs/Kconfig
index a7749c126b8e..bd21535a7620 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -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