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    SubjectRe: [RFC] ext3: per-process soft-syncing data=ordered mode
    > Greetings!
    >
    > data=ordered mode has proven reliable over the years, and it does this by
    > ordering filedata flushes before metadata flushes. But this sometimes
    > causes contention in the order of a 10x slowdown for certain apps, either
    > due to the misuse of fsync or due to inherent behaviour like db's, as well
    > as inherent starvation issues exposed by the data=ordered mode.
    >
    > data=writeback mode alleviates data=order mode slowdowns, but only works
    > per-mount and is too dangerous to run as a default mode.
    >
    > This RFC proposes to introduce a tunable which allows to disable fsync and
    > changes ordered into writeback writeout on a per-process basis like this:
    >
    > echo 1 > /proc/`pidof process`/softsync
    I guess disabling fsync() was already commented on enough. Regarding
    switching to writeback mode on per-process basis - not easily possible
    because sometimes data is not written out by the process which stored
    them (think of mmaped file). And in case of DB, they use direct-io
    anyway most of the time so they don't care about journaling mode anyway.
    But as Diego wrote, there is definitely some room for improvement in
    current data=ordered mode so the difference shouldn't be as big in the
    end.

    Honza
    --
    Jan Kara <jack@suse.cz>
    SuSE CR Labs


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