Re: [review] Remove the xfs refcache

[Lachlan McIlroy <lachlan@sgi.com>]

Christoph Hellwig wrote:
> On Mon, Dec 17, 2007 at 03:00:04PM +1100, Lachlan McIlroy wrote:
>> Hey hold on there buddy!  We may need to reactivate this code to fix some
>> performance issues.  I've acttually got this code working and proven that
>> it is one way to fix some of the NAS/NFS issues we have.
>>
>> The little comment that reads "reference cache not needed for NFS in 2.6"
>> is wrong - we do need it or something like it.
> 
> Not in XFS, though.  This thing needs to be done genericly in NFSD.
> Greg has been working on an open files cache in nfsd which should be
> helping this.
> 
> Adding a cache like this back into XFS will get my veto (at least for
> mainline where I have a bit of a say :))
> 

Greg's NFS OFC will provide better performance for strictly NFS workloads
and if all we are trying to fix here is the NFS issues then I agree with
you that the OFC should not go into XFS.

Since I have been able to reproduce some of our NAS/NFS performance problems
without NFS (that is demonstrate that the problems are in XFS) it makes some
sense to fix these in XFS.  I have observed that for some non-NFS workloads
we see a significant reduction in log traffic with the OFC in XFS so for
reasons beyond NFS there may be a need to reactivate the refcache code.  For
the moment we are still analysing the pros/cons.