> 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 <[EMAIL PROTECTED]>
SuSE CR Labs
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