From: Olga Kornievskaia Subject: Re: size of nfsv4 writes Date: Thu, 12 Jun 2008 17:41:53 -0400 Message-ID: <48519821.1040703@citi.umich.edu> References: <4846C586.1050000@citi.umich.edu> <1212597977.7422.4.camel@localhost> <48471180.8090208@citi.umich.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: Trond Myklebust , Chuck Lever , linux-nfs@vger.kernel.org To: Olga Kornievskaia Return-path: Received: from citi.umich.edu ([141.211.133.111]:2723 "EHLO citi.umich.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752299AbYFLVlz (ORCPT ); Thu, 12 Jun 2008 17:41:55 -0400 In-Reply-To: <48471180.8090208@citi.umich.edu> Sender: linux-nfs-owner@vger.kernel.org List-ID: Olga Kornievskaia wrote: > > > 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. Using Chuck's nfs-iostats to monitor an NFS write I can see that each operation writes about 830MB. Why is so much small than wsize=1M? > -- > To unsubscribe from this list: send the line "unsubscribe linux-nfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >