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Re: [Xen-devel] NFS related netback hang

On Fri, Apr 12, 2013 at 04:10:34AM +0100, G.R. wrote:
> Yes, it's not specific to NFS page, but I'm just bad luck enough.
> I agree with your suspect, the chance depends on the memory pressure in dom0.
> So here is a proper setup to reproduce the issue:
> 1. dom0 with SWAP disabled and with limited memory allocated.
> 2. domU serves storage and exports NFS
> 3. dom0 mounts the domU storage and writes to it.
> 4. You need to achieve high speed to expose this issue.

My setup is almost the same. The write speed is around
35-45MB/s if I do:

dd if=/dev/zero of=/mnt/t bs=1 count=200

However if I do count=2000, the speed slows down to 24MB/s. I suspect
that's the memory pressure in Dom0 - my Dom0 only has 1024MB Ram. But I
still didn't see any error.

> In my case, domU owns a dedicated SATA controller so there is no
> blkback overhead. Not sure if this is important factor to achieve high
> speed.
> And the transfer is a normal file copy instead of O_SYNC / O_DIRECT
> access so they can be cached in client side for some short period.
> Finally the transfer speed && memory size is crucial.
> With a 4GB memory allocate to dom0, I can copy a file (> 2GB) from a
> USB2 port without problem at about 32MB/s.
> But using a USB3 port, the same file generally sucks at 1.2GB. And the
> 'dd if=/dev/zero' sucks ever quicker.
> With around 1ï2GB memory to dom0, the freeze happens much earlier, but
> I did not check the exact time.

And I also use iperf, which can achieve 7GB/s transfer between Dom0 and
DomU, presumably that's fast enough?

> I'm on a custom build of xen 4.2.1 testing release (built around Jan
> this year?), with some patches related to graphics pass-through. But I
> guess the patch is not relevant.
> The dom0 kernel is version 3.6.11, 64 bit version.
> One thing I forgot to mention is the sign of memory leakage.
> I'm not very sure about it, but my dom0 reported OOM several days before.
> And typically I don't use dom0 for other purpose other than serve
> backends. The allocated memory should be around 2GB and that should be
> plenty for a dom0.
> Are there any known leakage bug out there?

Not that I know of, page allocation / deallocation in netback is quite


> Thanks,
> Timothy

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