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


Your comments are much welcome!


Thanks!

--
Al

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