nullfs changes MFC

[Dewayne Geraghty]

> -----Original Message-----
> From: owner-freebsd-stable at freebsd.org 
> [mailto:owner-freebsd-stable at freebsd.org] On Behalf Of 
> Konstantin Belousov
> Sent: Saturday, 8 December 2012 12:01 PM
> To: fs at freebsd.org
> Cc: stable at freebsd.org
> Subject: nullfs changes MFC
> 
> Hi,
> I am going to merge latest batch of the nullfs improvements 
> into stable/9. This will bring up significant performance 
> enchancements due to use of the shared locks for lookups if 
> the lower layer supports it, much better caching on the 
> nullfs layer, and proper handling of the text segments on the 
> nullfs. Also, it should improve the error recovery and some 
> corner cases with locking.
> 
> Unfortunately, the merge would break KBI for VFS, since it 
> needs 5 new VOP slots, and only three spares are left. We 
> already are very liberal with the VFS KBI, so I do not feel 
> that the merge is not acceptable, due to the benefits it 
> brings to the nullfs.
> 
> The merge is available at
> http://people.freebsd.org/~kib/misc/nullfs_9.1.patch
>

Konstantin,

Thank-you for these improvements.

I've been running this patchset on test and build servers for a few weeks and the systems remained stable and reliable.  

On some fairly complex jail and nullfs environments there has been an improvement in the order of 3 to 8% for large sequential
writes. 

Regards, Dewayne
PS I've reversed out the patches now they've migrated to RELENG_9