From: Olga Kornievskaia Subject: Re: size of nfsv4 writes Date: Wed, 04 Jun 2008 18:04:48 -0400 Message-ID: <48471180.8090208@citi.umich.edu> References: <4846C586.1050000@citi.umich.edu> <1212597977.7422.4.camel@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: Chuck Lever , linux-nfs@vger.kernel.org To: Trond Myklebust Return-path: Received: from citi.umich.edu ([141.211.133.111]:22478 "EHLO citi.umich.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758574AbYFDWEw (ORCPT ); Wed, 4 Jun 2008 18:04:52 -0400 In-Reply-To: <1212597977.7422.4.camel@localhost> Sender: linux-nfs-owner@vger.kernel.org List-ID: Trond Myklebust wrote: > On Wed, 2008-06-04 at 12:40 -0400, Olga Kornievskaia wrote: > >> While testing NFSv4 performance over the 10GE network, we are seeing the >> following behavior and would like to know if it is normal or a bug in >> the client code. >> >> The server offers the max_write of 1M. The client mounts the server with >> the "wsize" option of 1M. Yet during the write we are seeing that the >> write size is at most 49K. Why does client never come close to 1M limit? >> > > I have a feeling that is due to some crap in the VM. I'm currently > investigating a situation where it appears we're sending 1 COMMIT for > every 1-5 32k WRITEs. This is not a policy that stems from the NFS > client, so it would appear that the VM is being silly about things. > > I'm specially suspicious of the code in get_dirty_limits() that is > setting a limit to the number of dirty pages based on the number of > pages a given BDI has written out in the recent past. As far as I can > see, the intention is to penalise devices that are slow writers, but in > practice it doesn't do that: it penalises the devices that have the > least activity. > > I think we are seeing larger than usual number of COMMIT messages.