Re: NFS Hangs on heavy I/O

[Peter Staubach <staubach@redhat.com>]

Rajat wrote:
> Hi list,
>
> I am facing a NFS hang problem when I perform a very heavy I/O on a localhost 
> mount.
> The situation is:
> $>mount -t nfs localhost:/home/RHL /mnt/nfs
>
> where /home/RHL is a Ext3 Partition (/dev/sda5). Mount paramter was 'hard' by 
> default
>
> When I perform a heavy I/O on nfs mount
> $> createfile /mnt/nfs/huge_file 512 1048576
>
> Where createfile would try to write 512 blocks of 1048576 bytes each (each 
> system call of 1048576, 512 times = 512MB file).
>
> While the file is being created, I tried to ls in the /mnt/nfs directory - and 
> it hanged (after creating about 75MB file). Logging from other terminals was 
> not working as well.
> In my dmesg I found message saying:
>
> "nfs: server localhost not responding, still trying"
>
> [no other NFS related message here.]
>
> After rebooting, I tried the same thing but ls'd /home/RHL rather than nfs 
> mount - it hanged again (this time it could create 332MB file). Same message 
> was relayed in dmesg. This time I was able to login (though slow) and found 
> that 4 nfsd thread were there in ps.
> /proc/../status of all of them was "Sleeping" (for 2) or "Disk Sleep" (for 
> other 2). All were averaging about 97% sleep (got from /proc/.../status)
>
> I can reproduce this by the same procedure. 
>
> I am running a Intel Machine (Intel(R) Pentium(R) 4 CPU 3.20GHz HT), with 1GB 
> RAM, Linux-2.6.19 stock kernel, SATA driver (/dev/sda5) (default)
>
> I tried the same thing multiple times getting the same result (machine did not 
> stall always (just a couple of times)- nfs partition and the terminal on which 
> I was doing work always stalled).
>
> Can anyone help in giving pointer as to how can I find what is wrong. In case 
> you need some specific info, I would be glad to give.

This sounds like an old problem with mounting loopback.  The standard
recommendation is "don't do that, it will hang".

Peter Zijlstra has some changes for newer kernels which address this
situation.

In the meantime, either separate the client and the server or use
bind mounts.

       ps

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