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From: Christoph Hellwig <hch@lst.de>
To: Dan Williams <dan.j.williams@intel.com>,
	Vishal Verma <vishal.l.verma@intel.com>,
	Dave Jiang <dave.jiang@intel.com>
Cc: Mike Snitzer <snitzer@redhat.com>,
	Matthew Wilcox <willy@infradead.org>,
	linux-xfs@vger.kernel.org, nvdimm@lists.linux.dev,
	linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org
Subject: [PATCH 1/9] fsdax: improve the FS_DAX Kconfig description and help text
Date: Thu, 26 Aug 2021 15:55:02 +0200	[thread overview]
Message-ID: <20210826135510.6293-2-hch@lst.de> (raw)
In-Reply-To: <20210826135510.6293-1-hch@lst.de>

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
-- 
2.30.2


  reply	other threads:[~2021-08-26 13:57 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-26 13:55 dax_supported() related cleanups v2 Christoph Hellwig
2021-08-26 13:55 ` Christoph Hellwig [this message]
2021-08-26 13:55 ` [PATCH 2/9] dax: stop using bdevname Christoph Hellwig
2021-08-26 13:55 ` [PATCH 3/9] dm: use fs_dax_get_by_bdev instead of dax_get_by_host Christoph Hellwig
2021-08-26 14:42   ` Dan Williams
2021-08-26 16:19     ` Mike Snitzer
2021-08-26 13:55 ` [PATCH 4/9] dax: mark dax_get_by_host static Christoph Hellwig
2021-08-26 13:55 ` [PATCH 5/9] dax: move the dax_read_lock() locking into dax_supported Christoph Hellwig
2021-08-26 13:55 ` [PATCH 6/9] dax: remove __generic_fsdax_supported Christoph Hellwig
2021-08-26 13:55 ` [PATCH 7/9] dax: stub out dax_supported for !CONFIG_FS_DAX Christoph Hellwig
2021-08-26 13:55 ` [PATCH 8/9] xfs: factor out a xfs_buftarg_is_dax helper Christoph Hellwig
2021-08-26 14:37   ` Dan Williams
2021-08-26 15:11     ` Darrick J. Wong
2021-08-26 13:55 ` [PATCH 9/9] dax: remove bdev_dax_supported Christoph Hellwig
  -- strict thread matches above, loose matches on Subject: below --
2021-08-23 12:35 dax_supported() related cleanups Christoph Hellwig
2021-08-23 12:35 ` [PATCH 1/9] fsdax: improve the FS_DAX Kconfig description and help text Christoph Hellwig
2021-08-23 18:45   ` Dan Williams
2021-08-24  6:55     ` Christoph Hellwig

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