Re: NFS using too much memory on diskless system

[Neil Horman <nhorman@redhat.com>]

Gareth Glaccum wrote:
> Hi,
> I have a diskless system built and am having weird issues with the way 
> NFS client is working. I am using SLES 9.0 with the stock kernel 
> (2.6.5-7.111-30 I think from memory).
> I have mounted an NFS partition from another machine without any issues. 
> However, when I use anything to write to the partition (for example, see 
> later) the system uses memory to cache the files as I am mounted over GbE.
> However, the machine is not limiting the memory used at all. In fact, it 
> is using so much it is crashing the machine or causing other programs to 
> be OOM'd.
> 
> To recreate the problem, the following command took the machine out in 
> less than 3 seconds dd if=/dev/zero of=/mnt/NFSMOUNT bs=1024k count=4000 
> The machine has 4GB of memory and is using around 300Mb for its OS all 
> told.
> Is there some way of limiting the NFS cache size like there used to be 
> in the 2.4 kernel? (see section B7 of the nfs FAQ I believe)
> 
> Any ideas gratefully received,
> Gareth
> 
It sounds to me your kernel has some sort of vm bug, but if you want to 
shrink page cache usage, you may want to play with the dirty_vm_* 
settings in /proc/sys/vm.  I'm still getting used to the 2.6 sysctls, 
but I believe that those settings allow you to specify when your kernel 
decides its under sufficient memory pressure to start moving data back 
to disk.

HTH
Neil
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  *Neil Horman
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  *Red Hat, Inc.
  *nhorman@redhat.com
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