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SubjectRe: [PATCH] nfs: fix congestion control
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On Fri, 2007-01-19 at 18:57 +0100, Peter Zijlstra wrote:
> On Fri, 2007-01-19 at 09:20 -0800, Christoph Lameter wrote:
> > On Fri, 19 Jan 2007, Peter Zijlstra wrote:
> >
> > > + /*
> > > + * NFS congestion size, scale with available memory.
> > > + *
> >
> > Well this all depends on the memory available to the running process.
> > If the process is just allowed to allocate from a subset of memory
> > (cpusets) then this may need to be lower.
> >
> > > + * 64MB: 8192k
> > > + * 128MB: 11585k
> > > + * 256MB: 16384k
> > > + * 512MB: 23170k
> > > + * 1GB: 32768k
> > > + * 2GB: 46340k
> > > + * 4GB: 65536k
> > > + * 8GB: 92681k
> > > + * 16GB: 131072k
> >
> > Hmmm... lets say we have the worst case of an 8TB IA64 system with 1k
> > nodes of 8G each.
>
> Eeuh, right. Glad to have you around to remind how puny my boxens
> are :-)
>
> > On Ia64 the number of pages is 8TB/16KB pagesize = 512
> > million pages. Thus nfs_congestion_size is 724064 pages which is
> > 11.1Gbytes?
> >
> > If we now restrict a cpuset to a single node then have a
> > nfs_congestion_size of 11.1G vs an available memory on a node of 8G.
>
> Right, perhaps cap this to a max of 256M. That would allow 128 2M RPC
> transfers, much more would not be needed I guess. Trond?

That would be good as a default, but I've been thinking that we could
perhaps also add a sysctl in /proc/sys/fs/nfs in order to make it a
tunable?

Cheers,
Trond

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