From: "Jose R. Santos" <jrsantos@austin.ibm.com>
Subject: dentry/inode cache invalidation when using nfsd filesystem on 2.6
Date: Tue, 21 Oct 2003 08:07:02 -0500
Sender: nfs-admin@lists.sourceforge.net
Message-ID: <20031021130702.GQ1516@dbz.austin.ibm.com>
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To: Linux NFS Mailing List <nfs@lists.sourceforge.net>
Errors-To: nfs-admin@lists.sourceforge.net

Hi,

I have come across a interesting behavior when using NFS server on machines  
with large amounts of memory(16/32Gb).  If I have exported filesystems with  
lots of data and many directories that were access and had dentry/inode cache  
entries cached on the server, the clients took a long time(sometimes minutes)  
to mount the NFS exported directories.

While the client was mostly IDLE, the servers rpc.mountd thread was consuming  
100% of one CPU on the system.  After some digging, I found that the problem  
lies on the new nfsd filesystem code that talks to nfsctl.  Every time I issue  
a mount on the client, the server invalidates both inode and dentry caches.

Inode cache get invalidated on sys_nfsservctl(fs/nfsctl.c) on the fput call  
which eventually calls invalidate_inodes. Dentry caches get invalidated on  
do_open(fs/nfsctl.c) when calling do_kernel_mount which eventually calls  
shrink_dcache_sb.

The inode cache invalidation is easy to work around by just mounting the nfsd  
to something like /tmp/nfsd, but I haven't been able(except with a very  
dangerous and stupid patch) to work around the dentry cache invalidation.

This invalidation seem unnecessary and it cause by the interaction with this  
new interface for nfsctl.

Any help would be appreciated. :)

Thanks - JRS


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