Re: [PATCH] xfs: document zoned rt specifics in admin-guide

[Darrick J. Wong]

On Mon, Mar 31, 2025 at 09:15:00AM +0000, Hans Holmberg wrote:
> Document the lifetime, nolifetime and max_open_zones mount options
> added for zoned rt file systems.
> 
> Also add documentation describing the max_open_zones sysfs attribute
> exposed in /sys/fs/xfs/<dev>/zoned/
> 
> Fixes: 4e4d52075577 ("xfs: add the zoned space allocator")
> Signed-off-by: Hans Holmberg <hans.holmberg@xxxxxxx>

This is consistent with what I saw when the code went by, so
Reviewed-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>

--D

> ---
>  Documentation/admin-guide/xfs.rst | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
> 
> diff --git a/Documentation/admin-guide/xfs.rst b/Documentation/admin-guide/xfs.rst
> index b67772cf36d6..9d0344ce81f1 100644
> --- a/Documentation/admin-guide/xfs.rst
> +++ b/Documentation/admin-guide/xfs.rst
> @@ -124,6 +124,14 @@ When mounting an XFS filesystem, the following options are accepted.
>  	controls the size of each buffer and so is also relevant to
>  	this case.
>  
> +  lifetime (default) or nolifetime
> +	Enable data placement based on write life time hints provided
> +	by the user. This turns on co-allocation of data of similar
> +	life times when statistically favorable to reduce garbage
> +	collection cost.
> +
> +	These options are only available for zoned rt file systems.
> +
>    logbsize=value
>  	Set the size of each in-memory log buffer.  The size may be
>  	specified in bytes, or in kilobytes with a "k" suffix.
> @@ -143,6 +151,14 @@ When mounting an XFS filesystem, the following options are accepted.
>  	optional, and the log section can be separate from the data
>  	section or contained within it.
>  
> +  max_open_zones=value
> +	Specify the max number of zones to keep open for writing on a
> +	zoned rt device. Many open zones aids file data separation
> +	but may impact performance on HDDs.
> +
> +	If ``max_open_zones`` is not specified, the value is determined
> +	by the capabilities and the size of the zoned rt device.
> +
>    noalign
>  	Data allocations will not be aligned at stripe unit
>  	boundaries. This is only relevant to filesystems created
> @@ -542,3 +558,16 @@ The interesting knobs for XFS workqueues are as follows:
>    nice           Relative priority of scheduling the threads.  These are the
>                   same nice levels that can be applied to userspace processes.
>  ============     ===========
> +
> +Zoned Filesystems
> +=================
> +
> +For zoned file systems, the following attribute is exposed in:
> +
> +  /sys/fs/xfs/<dev>/zoned/
> +
> +  max_open_zones                (Min:  1  Default:  Varies  Max:  UINTMAX)
> +	This read-only attribute exposes the maximum number of open zones
> +	available for data placement. The value is determined at mount time and
> +	is limited by the capabilities of the backing zoned device, file system
> +	size and the max_open_zones mount option.
> -- 
> 2.34.1
>