linux-kernel - Re: 3.0+ NFS issues

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Date:	Wed, 30 May 2012 09:25:18 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Michael Tokarev <mjt@....msk.ru>
Cc:	linux-nfs@...r.kernel.org,
	Linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: 3.0+ NFS issues

On Wed, May 30, 2012 at 11:11:42AM +0400, Michael Tokarev wrote:
> On 29.05.2012 19:24, J. Bruce Fields wrote:
> > On Fri, May 25, 2012 at 10:53:11AM +0400, Michael Tokarev wrote:
> >> I updated my nfs server machine to kernel 3.0, and
> >> noticed that its main usage become, well, problematic.
> >>
> >> While trying to dig deeper, I also found a few other
> >> interesting issues, which are mentioned below.
> >>
> >> But first thing first: nfs.
> >>
> >> i686pae kernel, lots of RAM, Atom-based (cedar trail)
> >> machine with usual rtl8169 NIC.  3.0 or 3.2 kernel
> >> (I will try current 3.4 but I don't have much hopes
> >> there).  NFSv4.
> >>
> >> When a client machine (also 3.0 kernel) does some reading,
> >> the process often stalls somewhere in the read syscall,
> >> or, rarer, during close, for up to two MINUTES.  During
> >> this time, the client (kernel) reports "NFS server <foo>
> >> does not respond" several times, and finally "NFS server
> >> <foo> ok", client process "unstucks" from the read(2),
> >> and is able to perform a few more reads till the whole
> >> thing repeats.
> > 
> > You say 2.6.32 was OK; have you tried anything else between?
> 
> Well, I thought bisecting between 2.6.32 and 3.0 will be quite
> painful...  But I'll try if nothing else helps.  And no, I haven't
> tried anything in-between.
> 
> > And you're holding the client constant while varying only the server
> > version, right?
> 
> Yes.
> 
> > Is your network otherwise working?  (E.g. does transferring a bunch of
> > data from server to client using some other protocol work reliably?)
> 
> Yes, it works flawlessly, all other protocols works so far.
> 
> To the date, I resorted to using a small webserver plus wget as an ugly
> workaround for the problem - http works for reads from the server, while
> nfs works for writes.
> 
> > Is there anything happening on the network during these stalls?  (You
> > can watch the network with wireshark, for example.)
> 
> The network load is irrelevant - it behaves the same way with
> 100% idle network or with network busy doing other stuff.

That's not what I meant.  During one of these read stalls, if you watch
the network with wireshark, do you see any NFS traffic between the
client and server?

Also: do you have a reliable way of reproducing this quickly?

--b.

> > Does NFSv3 behave the same way?
> 
> Yes it does.  With all NFSDs on server eating all available CPUs for
> quite some time, and with being "ghosts" for perf top.
> 
> And with the client being unkillable again.
> 
> Can at least the client be made interruptible?  Mounting with
> -o intr,soft makes no visible difference...
> 
> Thanks,
> 
> /mjt
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