Al Boldi wrote:
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!
This is basically a kernel workaround for stupid app behavior. It wouldn't be
the first time we've provided such an option, but we shouldn't do it without a
very good justification. At the very least, we need a test case that
demonstrates the problem and benchmark results that prove that this approach
actually fixes it. I suspect we can find a cleaner fix for the problem.
-- Chris
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