From: "Benjamin Coddington" <bcodding@redhat.com>
To: "Matt Garman" <matthew.garman@gmail.com>
Cc: linux-nfs <linux-nfs@vger.kernel.org>
Subject: Re: Kerberized NFS client and slow user write performance
Date: Fri, 07 Oct 2016 13:06:35 -0400
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On 7 Oct 2016, at 12:43, Matt Garman wrote:

> We seem to be increasingly hit by this bug:
>
> https://access.redhat.com/solutions/2040223
> "On RHEL 6 NFS client usring kerberos (krb5), one user experiences
> slow write performance, another does not"
>
> You need a RH subscription to see that in its entirety.  But the
> subject basically says it all: randomly, one or more users will be
> subjected to *terrible* NFS write performance that persists until
> reboot.
>
> There is a root cause shown, but that is cryptic to non-kernel devs;
> it doesn't explain from a user perspective what triggers this state.
> (That's why it appears to be random to me.)
>
> There is no solution or workaround given.  This appears to be on a
> per-user + per-server basis, so a crude workaround is to migrate the
> user to a different server.  And we do regular reboots, which somewhat
> hides the problem.
>
> Does this bug also exist in upstream (i.e. non distro specific Linux
> NFS code)?  If so, is there any more detail on it, and/or a fix?

Hi Matt, a fix for this problem went in upstream:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=ce52914eb76efd62aa48d738cf845b37852bf920
which landed in 4.8.

I expect this will get fixed in RHEL6 and RHEL7 shortly, though I don't 
have
any BZ numbers handy..  let me know directly if you need them.

Ben