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From: Dan Williams <dan.j.williams@intel.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Vishal Verma <vishal.l.verma@intel.com>,
	Dave Jiang <dave.jiang@intel.com>,
	 Mike Snitzer <snitzer@redhat.com>,
	Matthew Wilcox <willy@infradead.org>,
	 linux-xfs <linux-xfs@vger.kernel.org>,
	Linux NVDIMM <nvdimm@lists.linux.dev>,
	 linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	linux-ext4 <linux-ext4@vger.kernel.org>
Subject: Re: [PATCH 1/9] fsdax: improve the FS_DAX Kconfig description and help text
Date: Mon, 23 Aug 2021 11:45:52 -0700	[thread overview]
Message-ID: <CAPcyv4h0QdHi10ngaXtuisxeZ+66wd-oy0F7r9C0FjJmyXBOFg@mail.gmail.com> (raw)
In-Reply-To: <20210823123516.969486-2-hch@lst.de>

On Mon, Aug 23, 2021 at 5:37 AM Christoph Hellwig <hch@lst.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.

> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  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"

  reply	other threads:[~2021-08-23 18:46 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
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 [this message]
2021-08-24  6:55     ` Christoph Hellwig
2021-08-23 12:35 ` [PATCH 2/9] dax: stop using bdevname Christoph Hellwig
2021-08-23 18:47   ` Dan Williams
2021-08-23 12:35 ` [PATCH 3/9] dm: use fs_dax_get_by_bdev instead of dax_get_by_host Christoph Hellwig
2021-08-23 19:02   ` Dan Williams
2021-08-23 12:35 ` [PATCH 4/9] dax: mark dax_get_by_host static Christoph Hellwig
2021-08-23 20:56   ` Dan Williams
2021-08-23 12:35 ` [PATCH 5/9] dax: move the dax_read_lock() locking into dax_supported Christoph Hellwig
2021-08-23 20:57   ` Dan Williams
2021-08-23 12:35 ` [PATCH 6/9] dax: remove __generic_fsdax_supported Christoph Hellwig
2021-08-23 21:10   ` Dan Williams
2021-08-23 12:35 ` [PATCH 7/9] dax: stub out dax_supported for !CONFIG_FS_DAX Christoph Hellwig
2021-08-23 21:15   ` Dan Williams
2021-08-24  5:44     ` Christoph Hellwig
2021-08-23 12:35 ` [PATCH 8/9] xfs: factor out a xfs_buftarg_is_dax helper Christoph Hellwig
2021-08-23 21:20   ` Dan Williams
2021-08-23 12:35 ` [PATCH 9/9] dax: remove bdev_dax_supported Christoph Hellwig
2021-08-23 21:22   ` Dan Williams
2021-08-26 13:55 dax_supported() related cleanups v2 Christoph Hellwig
2021-08-26 13:55 ` [PATCH 1/9] fsdax: improve the FS_DAX Kconfig description and help text Christoph Hellwig

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