Re: [PATCH 01/27] xfs: update mount options documentation

Eric Sandeen
2013-06-13T13:34:24Z

On 6/12/13 5:22 AM, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> Because it's horribly out of date.
>
> And mark various deprecated options as deprecated and give them a
> removal date.

thanks for doing this. some nitpicks below.

> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
> Documentation/filesystems/xfs.txt | 282 +++++++++++++++++++++++++------------
> 1 file changed, 192 insertions(+), 90 deletions(-)
>
> diff --git a/Documentation/filesystems/xfs.txt b/Documentation/filesystems/xfs.txt
> index 83577f0..28afbd1 100644
> --- a/Documentation/filesystems/xfs.txt
> +++ b/Documentation/filesystems/xfs.txt
> @@ -25,6 +25,13 @@ When mounting an XFS filesystem, the following options are accepted.
> Valid values for this option are page size (typically 4KiB)
> through to 1GiB, inclusive, in power-of-2 increments.
>
> + The default behaviour is for dynamic end-of-file
> + preallocation size, which uses a set of heuristics to
> + optimise the preallocation size based on the current
> + allocation patterns within the file and the access patterns
> + to the file. Specifying a fixed allocsize value turns off
> + the dynamic behaviour.
> +
> attr2/noattr2
> The options enable/disable (default is disabled for backward
> compatibility on-disk) an "opportunistic" improvement to be
> @@ -36,86 +43,108 @@ When mounting an XFS filesystem, the following options are accepted.
> CRC enabled filesystems always use the attr2 format, and so
> will reject the noattr2 mount option if it is set.
>
> - barrier
> - Enables the use of block layer write barriers for writes into
> - the journal and unwritten extent conversion. This allows for
> - drive level write caching to be enabled, for devices that
> - support write barriers.
> + barrier/nobarrier
> + Enables/disables the use of block layer write barriers for
> + writes into the journal and for data integrity operations.
> + This allows for drive level write caching to be enabled, for
> + devices that support write barriers.
>
> - discard
> - Issue command to let the block device reclaim space freed by the
> - filesystem. This is useful for SSD devices, thinly provisioned
> - LUNs and virtual machine images, but may have a performance
> - impact.
> + The default behaviour is to enable barriers.
>
> - dmapi
> - Enable the DMAPI (Data Management API) event callouts.
> - Use with the "mtpt" option.
> + discard/nodiscard
>
> - grpid/bsdgroups and nogrpid/sysvgroups
> - These options define what group ID a newly created file gets.
> - When grpid is set, it takes the group ID of the directory in
> - which it is created; otherwise (the default) it takes the fsgid
> - of the current process, unless the directory has the setgid bit
> - set, in which case it takes the gid from the parent directory,
> - and also gets the setgid bit set if it is a directory itself.
> + Enable/disable the issuing of commands to let the block
> + device reclaim space freed by the filesystem. This is
> + useful for SSD devices, thinly provisioned LUNs and virtual
> + machine images, but may have a performance impact.

should we talk about fstrim as an alternative here?

> - ihashsize=value
> - In memory inode hashes have been removed, so this option has
> - no function as of August 2007. Option is deprecated.
> + The default behaviour is disable discard commands.
> +
> + Note: It is currently recommended that you use the fstrim
> + application to discard unused blocks rather than the discard
> + mount option because the performance impact of this option
> + is quite severe.

oh right!

> + grpid/bsdgroups and nogrpid/sysvgroups
> + These options define what group ID a newly created file
> + gets. When grpid is set, it takes the group ID of the
> + directory in which it is created; otherwise (the default) it
> + takes the fsgid of the current process, unless the directory
> + has the setgid bit set, in which case it takes the gid from
> + the parent directory, and also gets the setgid bit set if it
> + is a directory itself.
> +
> + filestreams
> + Make the data allocator use the filestreams allocation mode
> + across the entire filesystem rather than just on directories
> + configured to use it.
>
> ikeep/noikeep
> - When ikeep is specified, XFS does not delete empty inode clusters
> - and keeps them around on disk. ikeep is the traditional XFS
> - behaviour. When noikeep is specified, empty inode clusters
> - are returned to the free space pool. The default is noikeep for
> - non-DMAPI mounts, while ikeep is the default when DMAPI is in use.
> + When ikeep is specified, XFS does not delete empty inode
> + clusters and keeps them around on disk. When noikeep is
> + specified, empty inode clusters are returned to the free
> + space pool.
> +
> + The default behaviour is delete inode clusters (noikeep).

is to delete inode clusters

>
> inode64
> - Indicates that XFS is allowed to create inodes at any location
> - in the filesystem, including those which will result in inode
> - numbers occupying more than 32 bits of significance. This is
> - the default allocation option. Applications which do not handle
> - inode numbers bigger than 32 bits, should use inode32 option.
> + When inode64 is specified, it indicates that XFS is allowed
> + to create inodes at any location in the filesystem,
> + including those which will result in inode numbers occupying
> + more than 32 bits of significance. Applications which do
> + not handle inode numbers bigger than 32 bits should use
> + inode32 option.

While we're rewriting . . . applications don't use mount options,
not really. So maybe:

If applications are in use which do not handle inode numbers bigger
than 32 bits, the inode32 option should be specified.

> + This is the default allocation behaviour, even on 32 bit
> + machines when neither inode64 or inode32 is specified.
>
> inode32
> - Indicates that XFS is limited to create inodes at locations which
> - will not result in inode numbers with more than 32 bits of
> - significance. This is provided for backwards compatibility, since
> - 64 bits inode numbers might cause problems for some applications
> - that cannot handle large inode numbers.
> + When inode32 is specified, it indicates that XFS limits
> + inode creation to locations which will not result in inode
> + numbers with more than 32 bits of significance. This is
> + provided for backwards compatibility with older systems and
> + applications, since 64 bits inode numbers might cause
> + problems for some applications that cannot handle large
> + inode numbers.

Any point to talking about what this does to locality etc?

> largeio/nolargeio
> If "nolargeio" is specified, the optimal I/O reported in
> - st_blksize by stat(2) will be as small as possible to allow user
> - applications to avoid inefficient read/modify/write I/O.
> - If "largeio" specified, a filesystem that has a "swidth" specified
> - will return the "swidth" value (in bytes) in st_blksize. If the
> - filesystem does not have a "swidth" specified but does specify
> - an "allocsize" then "allocsize" (in bytes) will be returned
> - instead.
> + st_blksize by stat(2) will be as small as possible to allow
> + user applications to avoid inefficient read/modify/write
> + I/O. This is typically the page size of the machine, as
> + this is the granularity of the page cache.
> +
> + If "largeio" specified, a filesystem that was created with a
> + "swidth" specified will return the "swidth" value (in bytes)
> + in st_blksize. If the filesystem does not have a "swidth"
> + specified but does specify an "allocsize" then "allocsize"
> + (in bytes) will be returned instead. Otherwise the behaviour
> + is the same as if "nolargeio" was specified.
> +
> If neither of these two options are specified, then filesystem
> will behave as if "nolargeio" was specified.

I have to wonder when anyone would want to use largeio. This doesn't
tell me, either. ;)

I wonder if there's any clearer way to show defaults. Maybe:

largeio
nolargeio (*)
If "nolargeio" is specified, the optimal I/O reported in
...

> logbufs=value
> - Set the number of in-memory log buffers. Valid numbers range
> - from 2-8 inclusive.
> - The default value is 8 buffers for filesystems with a
> - blocksize of 64KiB, 4 buffers for filesystems with a blocksize
> - of 32KiB, 3 buffers for filesystems with a blocksize of 16KiB
> - and 2 buffers for all other configurations. Increasing the
> - number of buffers may increase performance on some workloads
> - at the cost of the memory used for the additional log buffers
> - and their associated control structures.
> + Set the number of in-memory log buffers. Valid numbers
> + range from 2-8 inclusive.
> +
> + The default value is 8 buffers.
> +
> + If the memory cost of 8 log buffers is too high on small
> + systems, then it may be reduced at some cost to performance
> + on metadata intensive workloads.

The logbsize option below controls the size of each buffer.

> logbsize=value
> - Set the size of each in-memory log buffer.
> - Size may be specified in bytes, or in kilobytes with a "k" suffix.
> - Valid sizes for version 1 and version 2 logs are 16384 (16k) and
> - 32768 (32k). Valid sizes for version 2 logs also include
> - 65536 (64k), 131072 (128k) and 262144 (256k).
> - The default value for machines with more than 32MiB of memory
> - is 32768, machines with less memory use 16384 by default.
> + Set the size of each in-memory log buffer. The size may be
> + specified in bytes, or in kilobytes with a "k" suffix.
> + Valid sizes for version 1 and version 2 logs are 16384 (16k)
> + and 32768 (32k). Valid sizes for version 2 logs also
> + include 65536 (64k), 131072 (128k) and 262144 (256k). The
> + version 2 log size must be an integer multiple of the log
> + stripe unit configured at mkfs time.

the version 2 log size, or logbsize?

> + The default value for for version 1 logs is 32768, while the
> + default value for version 2 logs is MAX(32768, log_sunit).
>
> logdev=device and rtdev=device
> Use an external log (metadata journal) and/or real-time device.
> @@ -124,16 +153,12 @@ 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.
>
> - mtpt=mountpoint
> - Use with the "dmapi" option. The value specified here will be
> - included in the DMAPI mount event, and should be the path of
> - the actual mountpoint that is used.
> -
> noalign
> - Data allocations will not be aligned at stripe unit boundaries.
>
> - noatime
> - Access timestamps are not updated when a file is read.
> + Data allocations will not be aligned at stripe unit
> + boundaries. This is only relevant to filesystems created
> + with non-zero data alignment parameters (sunit, swidth) by
> + mkfs.

why would I use this?

> norecovery
> The filesystem will be mounted without running log recovery.
> @@ -144,8 +169,14 @@ When mounting an XFS filesystem, the following options are accepted.
> the mount will fail.
>
> nouuid
> - Don't check for double mounted file systems using the file system uuid.
> - This is useful to mount LVM snapshot volumes.
> + Don't check for double mounted file systems using the file
> + system uuid. This is useful to mount LVM snapshot volumes,
> + and often used in combination with "norecovery" for mounting
> + read-only snapshots.
> +
> + noquota
> + Forcibly turns off all quota accounting and enforcement
> + within the filesystem.
>
> uquota/usrquota/uqnoenforce/quota
> User disk quota accounting enabled, and limits (optionally)
> @@ -160,24 +191,68 @@ When mounting an XFS filesystem, the following options are accepted.
> enforced. Refer to xfs_quota(8) for further details.
>
> sunit=value and swidth=value
> - Used to specify the stripe unit and width for a RAID device or
> - a stripe volume. "value" must be specified in 512-byte block
> - units.
> - If this option is not specified and the filesystem was made on
> - a stripe volume or the stripe width or unit were specified for
> - the RAID device at mkfs time, then the mount system call will
> - restore the value from the superblock. For filesystems that
> - are made directly on RAID devices, these options can be used
> - to override the information in the superblock if the underlying
> - disk layout changes after the filesystem has been created.
> - The "swidth" option is required if the "sunit" option has been
> - specified, and must be a multiple of the "sunit" value.
> + Used to specify the stripe unit and width for a RAID device
> + or a stripe volume. "value" must be specified in 512-byte
> + block units. These options are only relevant to filesystems
> + that were created with non-zero data alignment parameters.

(i.e. su/sw or sunit/swidth was specified at mkfs time).

> +
> + The sunit and swidth parameters specified must be compatible
> + with the existing filesystem alignment characteristics. If
> + the filesystem was not created with data alignment
> + constraints, then it may be impossible to set a valid sunit
> + (and hence swidth) value. In general, that means the only
> + valid changes to sunit are increasing it by a power-of-2
> + multiple. Valid swidth values are any integer multiple of a
> + valid sunit value.

now I'm confused. It's only relevant to a filesystem w/ geometry
specified, but if it wasn't specified, it may be possible . . . ?

And if nothing was specified (i.e. 0 su/sw) then we can only increase
that 0 by a power of 2?

> + For filesystems that have existing data alignment values on
> + disk (i.e. specified by mkfs), any new valid values passed
> + in as mount options will overwrite the values stored on
> + disk. Hence this mount option does not need to be specified
> + for every mount operation in this case.

so I think this all needs to clarify whether it works on filesystems
w/o existing geometry, or not. And "why you might want this" would
be helpful too.

> swalloc
> Data allocations will be rounded up to stripe width boundaries
> when the current end of file is being extended and the file
> size is larger than the stripe width size.
>
> + wsync
> + When specified, all filesystem namespace operations are
> + executed synchronously. This ensures that when the namespace
> + operation (create, unlink, etc) completes, the change to the
> + namespace is on stable storage. This is useful in HA setups
> + where failover must not result in clients seeing
> + inconsistent namespace presentation during or after a
> + failover event.
> +
> +
> +Deprecated Mount Options
> +========================
> +
> + delaylog/nodelaylog
> + Delayed logging is the only logging method that XFS supports
> + now, so these mount options are now ignored.
> +
> + Due for removal in 3.12.
> +
> + ihashsize=value
> + In memory inode hashes have been removed, so this option has
> + no function as of August 2007. Option is deprecated.
> +
> + Due for removal in 3.12.
> +
> + irixsgid
> + This behaviour is now controlled by a sysctl, so the mount
> + option is ignored.
> +
> + Due for removal in 3.12.
> +
> + osyncisdsync
> + osyncisosync
> + O_SYNC and O_DSYNC are fully supported, so there is no need
> + for these options any more.
> +
> + Due for removal in 3.12.

> sysctls
> =======
> @@ -189,15 +264,20 @@ The following sysctls are available for the XFS filesystem:
> in /proc/fs/xfs/stat. It then immediately resets to "0".
>
> fs.xfs.xfssyncd_centisecs (Min: 100 Default: 3000 Max: 720000)
> - The interval at which the xfssyncd thread flushes metadata
> - out to disk. This thread will flush log activity out, and
> - do some processing on unlinked inodes.
> + The interval at which the filesystem flushes metadata
> + out to disk and runs internal cache cleanup routines.
>
> - fs.xfs.xfsbufd_centisecs (Min: 50 Default: 100 Max: 3000)
> - The interval at which xfsbufd scans the dirty metadata buffers list.
> + fs.xfs.filestream_centisecs (Min: 1 Default: 3000 Max: 360000)
> + The interval at which the filesystem ages filestreams cache
> + references and returns timed-out AGs back to the free stream
> + pool.

I bet Documentation/filesystem/xfs-filestreams.txt would be handy, but *shrug*

> - fs.xfs.age_buffer_centisecs (Min: 100 Default: 1500 Max: 720000)
> - The age at which xfsbufd flushes dirty metadata buffers to disk.
> + fs.xfs.speculative_prealloc_lifetime
> + (Units: seconds Min: 1 Default: 300 Max: 86400)
> + The interval at which the background scanning for inodes
> + with unused speculative preallocation runs at. The scan

The interval at which the background scanning . . . runs. (no at.)

> + removes unused preallocation from clean inodes and releases
> + the unused space back to the free pool.
>
> fs.xfs.error_level (Min: 0 Default: 3 Max: 11)
> A volume knob for error reporting when internal errors occur.
> @@ -254,9 +334,31 @@ The following sysctls are available for the XFS filesystem:
> by the xfs_io(8) chattr command on a directory to be
> inherited by files in that directory.
>
> + fs.xfs.inherit_nodefrag (Min: 0 Default: 1 Max: 1)
> + Setting this to "1" will cause the "nodefrag" flag set
> + by the xfs_io(8) chattr command on a directory to be
> + inherited by files in that directory.
> +
> fs.xfs.rotorstep (Min: 1 Default: 1 Max: 256)
> In "inode32" allocation mode, this option determines how many
> files the allocator attempts to allocate in the same allocation
> group before moving to the next allocation group. The intent
> is to control the rate at which the allocator moves between
> allocation groups when allocating extents for new files.
> +
> +Deprecated Sysctls
> +==================
> +
> + fs.xfs.xfsbufd_centisecs (Min: 50 Default: 100 Max: 3000)
> + Dirty metadata is now tracked by the log subsystem and
> + flushing is driven by log space and idling demands. The
> + xfsbufd no longer exists, so this syctl does nothing.
> +
> + Due for removal in 3.14.
> +
> + fs.xfs.age_buffer_centisecs (Min: 100 Default: 1500 Max: 720000)
> + Dirty metadata is now tracked by the log subsystem and
> + flushing is driven by log space and idling demands. The
> + xfsbufd no longer exists, so this syctl does nothing.
> +
> + Due for removal in 3.14.
>