Re: What's the NFS OOM problem?

[Roger Heflin]

Neil Brown wrote:
> On Thursday August 10, w@xxxxxx wrote:
> > > Can someone help me and give me a brief description on OOM issue?
> > I don't know about any OOM issue related to NFS. At most it might happen
> > on the client (eg: stating firefox from an NFS root) which might not have
> > enough memory for new network buffers, but I don't even know if it's
> > possible at all.
>
> We've had reports of OOM problems with NFS at SuSE.
> The common factors seem to be lots of memory (6G+) and very large
> files. 
> Tuning down  /proc/sys/vm/dirty_*ratio seems to avoid the problem,
> but I'm not very close to understanding what the real problem is.
>
> NeilBrown
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I have noticed on SLES kernels that when the dirty_*ratios turned down it
still uses alot more memory than it should work writeback buffers, it makes
me think that with the default setting of 40% that it for some reason
may be using all of memory and deadlocking.   It does not seem like an
NFS only issue, as I believe I have duplicated it with a fast lock
setup.

Checking writeback in /proc/meminfo does indicate that alot more memory
is being used for write cache that should be.

                                    Roger
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