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    Subjectsupporting laptops fs-semantic changes (was Re: Ext4 and the "30 second window of death")
    Matthew Garrett wrote:
    >> The other subtlety comes if we add fsync() suppression to laptop mode
    Perhaps this has already been suggested, but rather than
    adding all these semantics to the core file-system / kernel routines,
    wouldn't it be preferable to allow some 'layering' of a pseudo,
    memory-based file-system, OVER some 'real' file system (OR), definable
    set of files (under a subdir...or same device...or whatever).

    The semantics of when the virtual-fs would sync to the physical-fs/files
    controlled via mount options. Physical disk writes would be controlled by
    selectively ignoring or honoring various "sync" events (time expired,
    sync, fsync).

    This could allow file-systems with different 'needs' (DB, or otherwise)
    to be treated differently.

    The advantage of another layer, is you could define _how much_ buffering
    you wanted to allocate to a filesystem (or file-set). Maybe it's tolerable
    losing a audio-recording of a talk, so large buff + don't sync 'cept when
    full is fine. Sensitive filesystems(or sets) (i.e. db's), could be set
    with buffers to hold largest 'single-writes', but sync/fsyncs are what
    they are.

    An optimization could provide for read/writes through the user-mem
    buffered 'fs', to do direct I/O rather than into normal file-buffs where
    possible, since presumably all accesses to a file would go through the
    layer or not.

    Wouldn't require application changing, and wouldn't require changing
    well defined, lower-level kernel-filesystem operations.

    Just a thought.

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