On Mon, Aug 23, 2021 at 5:37 AM Christoph Hellwig <hch@xxxxxx> wrote: > > 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. > Looks good, nice improvement. A couple suggestions below. > Signed-off-by: Christoph Hellwig <hch@xxxxxx> > --- > fs/Kconfig | 17 ++++++++++++++--- > 1 file changed, 14 insertions(+), 3 deletions(-) > > diff --git a/fs/Kconfig b/fs/Kconfig > index a7749c126b8e..37e4441119cf 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 +53,19 @@ 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 There's still the concern that on systems with small amount of DRAM relative to large amounts of PMEM that --map=mem might consume all available memory for 'struct page'. Perhaps just add: "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 enable > + globally or per-inode using a mount option as well. See the > + file system documentation for details. How about include the link? "See the file system documentation for details: https://www.kernel.org/doc/html/latest/filesystems/dax.html";
