Re: [Linux-cachefs] Re: NFS Patch for FSCache

[David Howells <dhowells@redhat.com>]

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.

David