nfs client stat() performance degradation

[Julien Cristau <julien.cristau@logilab.fr>]

Hi,

we're experiencing some troubling performance issues with our nfs clients.  One
of the symptoms is degraded performance of directory walks with hot caches and
expired attribute caches: "find -ls" in the kernel tree goes from about 4s
(cold caches) to 1.5s (hot vm caches) and then to 18s after actimeo.  Network
traffic increases by about the same amount.  "echo 3 >
/proc/sys/vm/drop_caches" brings back the initial performance (~4s), but so do
writing 1 or 2.

This was reported almost two years ago in https://bugs.debian.org/702477 but I
don't know if this is a known issue upstream.  Seen on various kernel versions,
up to 3.18.

Is there anything we can do to track this down, or are there known workarounds
for this?

Thanks,
Julien
-- 
Julien Cristau          <julien.cristau@logilab.fr>
Logilab		        http://www.logilab.fr/
Informatique scientifique & gestion de connaissances