On 2016-02-22 11:05:20 -0500, Tom Lane wrote:
> Andres Freund <and...@anarazel.de> writes:
> > Interesting. That doesn't reflect my own tests, even on rotating media,
> > at all. I wonder if it's related to:
> > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=23d0127096cb91cb6d354bdc71bd88a7bae3a1d5
> > If you use your 12.04 kernel, that'd not be fixed. Which might be a
> > reason to do it as you suggest.
> Hmm ... that kernel commit is less than 4 months old.  Would it be
> reflected in *any* production kernels yet?

Probably not - so far I though it mainly has some performance benefits
on relatively extreme workloads; where without the patch, flushing still
is better performancewise than not flushing. But in the scenario Fabien
has brought up it seems quite possible that sync_file_range emitting
"storage cache flush" instructions, could explain the rather large
performance difference between his and my experiments.



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