linux-kernel - Re: High load in 2.6.27, NFS / rpcauth_lookup

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Message-ID: <20081027095843.GA10937@squirrel.roonstrasse.net>
Date:	Mon, 27 Oct 2008 10:58:43 +0100
From:	Max Kellermann <max@...mpel.org>
To:	Trond Myklebust <trond.myklebust@....uio.no>
Cc:	linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org
Subject: Re: High load in 2.6.27, NFS / rpcauth_lookup_credcache()?

On 2008/10/24 20:09, Trond Myklebust <trond.myklebust@....uio.no> wrote:
> OK, could you please describe your environment a bit. Do you have lots
> of different users logged in at the same time, or do you perhaps use
> newgrp or su to switch uid/gids a lot on your processes?
> I'm trying to see if there might be a reason for the lookup in the
> credcache being such a heavy duty operation in your setup.

It's a web server for shared hosting.  The web space is mounted via
NFSv3 from a NetApp.  There is a huge number of web sites on this
cluster.  All web sites are owned by the same UID, and the web server
runs as a different UID (read-only access).

Each time a CGI starts, its uid is changed to the one "owner" UID
(similar to mod_suexec, but there's only one UID for all customer
accounts).  Each time a CGI starts, its chroot (pivot_root) is
constructed with several bind mounts (in a separate namespace with
CLONE_NEWNS).

There are no new users or groups being created.  There are only 2 UIDs
accessing NFS: the webserver (ro) and CGI (rw).

Max
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