Re: [PATCH] nfs: fix congestion control

[Peter Zijlstra]

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?

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