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    Subject(Lack of) i_version handling in udf
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    Date
    Jan,

    Re: [PATCH v4 00/19] fs: rework and optimize i_version handling in filesystems

    On 12/22/2017 06:05 AM, Jeff Layton wrote:

    > The inode->i_version field is supposed to be a value that changes
    > whenever there is any data or metadata change to the inode. Some
    > filesystems use it internally to detect directory changes during
    > readdir. knfsd will use it if the filesystem has MS_I_VERSION set. IMA
    > will also use it to optimize away some remeasurement if it's available.
    > NFS and AFS just use it to store an opaque change attribute from the
    > server.
    >
    > Only btrfs, ext4, and xfs increment it for data changes. Because of
    > this, these filesystems must log the inode to disk whenever the
    > i_version counter changes. That has a non-zero performance impact,
    > especially on write-heavy workloads, because we end up dirtying the
    > inode metadata on every write, not just when the times change.
    >
    > It turns out though that none of these users of i_version require that
    > it change on every change to the file. The only real requirement is that
    > it be different if something changed since the last time we queried for
    > it.
    >
    > If we keep track of when something queries the value, we can avoid
    > bumping the counter and an on-disk update when nothing else has changed
    > if no one has queried it since it was last incremented.

    This happened to cross my radar, which made me think...is it a problem
    that the UDF driver does not have any references to i_version at all?
    I suppose R/W UDF is a small subset of the normal use cases, but the driver
    does try to support it.

    Regards,
    ------------------------------------------------------------------------
    Steven J. Magnani "I claim this network for MARS!
    www.digidescorp.com Earthling, return my space modulator!"

    #include <standard.disclaimer>

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