[ kvm-Bugs-2327497 ] NFS copy makes guest network unstable

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Bugs item #2327497, was opened at 2008-11-22 17:53
Message generated for change (Comment added) made by avik
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Jiajun Xu (jiajun)
Assigned to: Nobody/Anonymous (nobody)
Summary: NFS copy makes guest network unstable

Initial Comment:
The NFS network of KVM guest is very unstable. When we copy a >600M file to the guest by NFS mount. The guest's network will down after finishing at about 500M size. 
Then, guest's network is down. Host also can not use "ping" or "scp". And sometimes, host also complains: ping: sendmsg: No buffer space available. I see memory by 'free', there is only 69MB free (While totally 8GB on the machine!).

Using scp to copy file can not reproduce it. This issue is very easy to be reproduced (>50%). 


Reproduce steps:
----------------
1. Create a guest and config NFS sharing folder on it
2. Mount the nfs folder to local folder --- /media
3. cp xxx /media
4. After some time, guest network is down


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>Comment By: Avi Kivity (avik)
Date: 2008-11-23 20:40

Message:
Is this a regression, or a new test?

It it is a regression, what was the last version that worked?

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Comment By: Fabio Coatti (cova)
Date: 2008-11-23 17:12

Message:
I can confirm a similar behaviour: a kvm machines gets large amounts of
data via http protocol and saves that files over NFS. (file sizes are in
the range of 4-20 MB approx and the machine downloads several of that
files.) After some time (I don't have a precise figure, but some hundreds
of MB) the guest nework goes down. No answers even to ping coming from
outside.
the guest uses virtio network drivers (as normal drivers are way too
slow)
host machine: 64 bit AMD dual quad core 16GB, tried with several kernels
ranging from 2.6.27.4 to 2.6.25.19
guest: 32 bit kvm machines (tried 76/77/78 ). both UP and SMP
configuration. kernels: same as host machine
network setup:
bridged network with br0 device on host machine. We are using 2 vlans for
guest and we have tried all the configuration (single tap and vlans
resolved on guest side,then two tap so two interfaces on guest machine and
so on) without any improvement. I can exclude MTU issues, as we have seen
that and solved, this issue is completely different.
At some point, sniffing traffic on host interfaces we are able to see only
ARP requests coming from guest, nothing more.

I understand that data is in no way complete, but I'm willing to do any
debug if someone gives me any hint on how to do so correctly. Thanks.


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