From mboxrd@z Thu Jan  1 00:00:00 1970
From: Joe Thornber <thornber@redhat.com>
Subject: Re: DM-Cache Writeback & Direct IO?
Date: Wed, 8 Jul 2015 15:48:29 +0100
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On Wed, Jul 08, 2015 at 11:03:42AM +0200, Christoph Nelles wrote:
> Hi,
> 
> Can the dm-cache writeback cache buffer direct IO or goes direct IO
> always immediately to the origin device?

Yes, the device mapper layer knows nothing about direct IO vs page
cache IO.

> I am currently performing tests and see that random direct write IO
> never hits the cache, even after overwriting the same region over
> and over.

Could you try with the latest kernels and the new smq policy please?

- Joe