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Date: Tue, 24 Aug 2021 08:55:46 +0200 From: Christoph Hellwig <hch@....de> To: Dan Williams <dan.j.williams@...el.com> Cc: Christoph Hellwig <hch@....de>, Vishal Verma <vishal.l.verma@...el.com>, Dave Jiang <dave.jiang@...el.com>, Mike Snitzer <snitzer@...hat.com>, Matthew Wilcox <willy@...radead.org>, linux-xfs <linux-xfs@...r.kernel.org>, Linux NVDIMM <nvdimm@...ts.linux.dev>, linux-fsdevel <linux-fsdevel@...r.kernel.org>, linux-ext4 <linux-ext4@...r.kernel.org> Subject: Re: [PATCH 1/9] fsdax: improve the FS_DAX Kconfig description and help text On Mon, Aug 23, 2021 at 11:45:52AM -0700, Dan Williams wrote: > On Mon, Aug 23, 2021 at 5:37 AM Christoph Hellwig <hch@....de> 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. Does this looks ok? --- >From c69617137a1e6b67122c871c946e7aa00b03978b Mon Sep 17 00:00:00 2001 From: Christoph Hellwig <hch@....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@....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 -- 2.30.2
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