Re: [PATCH 1/9] fsdax: improve the FS_DAX Kconfig description and help text
From: Christoph Hellwig <hch@lst.de>
Date: 2021-08-24 06:55:53
Also in:
linux-fsdevel, linux-xfs, nvdimm
Subsystem:
filesystems (vfs and infrastructure), the rest · Maintainers:
Alexander Viro, Christian Brauner, Linus Torvalds
On Mon, Aug 23, 2021 at 11:45:52AM -0700, Dan Williams wrote:
On Mon, Aug 23, 2021 at 5:37 AM Christoph Hellwig [off-list ref] wrote:quoted
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.
Does this looks ok? --- From c69617137a1e6b67122c871c946e7aa00b03978b Mon Sep 17 00:00:00 2001 From: Christoph Hellwig <hch@lst.de> Date: Mon, 23 Aug 2021 10:57:37 +0200 Subject: 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> --- fs/Kconfig | 21 ++++++++++++++++++--- 1 file 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
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2.30.2