Re: Re: NFS Patch for FSCache

[Troy Benjegerdes <hozer@hozed.org>]

On Tue, May 10, 2005 at 08:12:51PM +0100, David Howells wrote:
> 
> Steve Dickson <SteveD@redhat.com> wrote:
> 
> > But the real saving, imho, is the fact those reads were measured after the
> > filesystem was umount then remounted. So system wise, there should be some
> > gain due to the fact that NFS is not using the network....
> 
> I tested md5sum read speed also. My testbox is a dual 200MHz PPro. It's got
> 128MB of RAM. I've got a 100MB file on the NFS server for it to read.
> 
> 	No Cache:	~14s
> 	Cold Cache:	~15s
> 	Warm Cache:	~2s
> 
> Now these numbers are approximate because they're from memory.
> 
> Note that a cold cache is worse than no cache because CacheFS (a) has to check
> the disk before NFS goes to the server, and (b) has to journal the allocations
> of new data blocks. It may also have to wait whilst pages are written to disk
> before it can get new ones rather than just dropping them (100MB is big enough
> wrt 128MB that this will happen) and 100MB is sufficient to cause it to start
> using single- and double-indirection pointers to find its blocks on disk,
> though these are cached in the page cache.

How big was the cachefs filesystem?

Now try reading a 1GB file over nfs..

I have found (with openafs), that I either need a really small cache, or
a really big one.. The bigger the openafs cache gets, the slower it
goes. The only place i run with a > 1GB openafs cache is on an imap
server that has an 8gb cache for maildirs.