[Linux-cluster] GFS: fh2dentry misses

[Wendy Cheng]

Chad Slater wrote:
> While troubleshooting some GFS performance issues, I came across this 
> when viewing the counters:
>  
> fh2dentry misses 292928
>  
> What is fh2dentry misses?

This symbol name is kind of mis-leading. It is actually a counter of 
"inode miss".  With Linux NFS implementation, each nfs file handle has 
file inode embedded in it. When client sends file handle to the server, 
nfsd passes the file handle to GFS (or any filesystem). GFS will check 
to see whether the subject inode is still in the memory cache. If not, 
it increments this counter and re-do lookup. As any filesystem, lookup 
is normally expensive since it involves disk read. The more cache 
misses, the slower your performance will be.

-- Wendy