[Bugs] [Bug 1375959] Files not being opened with o_direct flag during random read operation ( Glusterfs 3.8.2)

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1375959

Pranith Kumar K <pkarampu at redhat.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|bugs at gluster.org            |kdhananj at redhat.com



--- Comment #7 from Pranith Kumar K <pkarampu at redhat.com> ---
(In reply to Krutika Dhananjay from comment #5)
> (In reply to Pranith Kumar K from comment #3)
> > Shekhar,
> >    You need the following two options for O_DIRECT to be handled properly:
> > 
> > 1) performance.strict-o-direct on
> > 2) network.remote-dio off
> > 
> > Pranith
> 
> @Pranith - Part of the problem seems to be that the anonymous fds created by
> open-behind don't inherit the original open() flags. And when ob does wind
> reads and writes on these anon fds, posix winds up using the usual
> GF_ANON_FD_FLAGS (O_RDWR|O_LARGEFILE) value at the time of open() preceding
> the invoked fd operation (mostly read/write).

As soon as the first write comes, an OPEN FOP with same flags that came at the
time of open() are sent out from open-behind, from then on even the reads are
served using this fd. Could you confirm if the test includes only reads and no
writes at all? In that case we have a bug we need to look into.

> 
> FWIW, I did try the same test Shekhar ran on my test cluster and disabling
> open-behind in addition to the two already known o-direct options that you
> mentioned above, seemed to fix the issue of growing cache size as the test
> progresses (although it didn't have any effect as per Shekhar when he tried
> the same).
> 
> I am yet to confirm the theory (and the presence/absence of O_DIRECT flag at
> the level of posix) through strace output of the bricks with and without
> open-behind. I will do the same tomorrow and update the bug.

Yes, this would be important to know.

> 
> -Krutika

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