From: Martin Knoblauch Subject: Re: [RFC][Resend] Make NFS-Client readahead tunable Date: Thu, 18 Sep 2008 01:38:57 -0700 (PDT) Message-ID: <124712.40022.qm@web32602.mail.mud.yahoo.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Greg Banks , linux-nfs list , linux-kernel@vger.kernel.org, Peter zijlstra To: Andrew Morton Return-path: Received: from web32602.mail.mud.yahoo.com ([68.142.207.229]:46053 "HELO web32602.mail.mud.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1753266AbYIRIi7 (ORCPT ); Thu, 18 Sep 2008 04:38:59 -0400 Sender: linux-nfs-owner@vger.kernel.org List-ID: ----- Original Message ---- > From: Andrew Morton > To: Martin Knoblauch > Cc: Greg Banks ; linux-nfs list ; linux-kernel@vger.kernel.org > Sent: Thursday, September 18, 2008 10:18:18 AM > Subject: Re: [RFC][Resend] Make NFS-Client readahead tunable > > On Thu, 18 Sep 2008 00:42:58 -0700 (PDT) Martin Knoblauch > wrote: > > > ----- Original Message ---- > > > > > From: Andrew Morton > > > To: Greg Banks > > > Cc: Martin Knoblauch ; linux-nfs list > ; linux-kernel@vger.kernel.org > > > Sent: Thursday, September 18, 2008 5:13:34 AM > > > Subject: Re: [RFC][Resend] Make NFS-Client readahead tunable > > > > > > On Thu, 18 Sep 2008 11:42:54 +1000 Greg Banks wrote: > > > > > > > I think having a tunable for client readahead is an excellent idea, > > > > although not to solve your particular problem. The SLES10 kernel has a > > > > patch which does precisely that, perhaps Neil could post it. > > > > > > > > I don't think there's a lot of point having both a module parameter and > > > > a sysctl. > > > > > > mount -o remount,readahead=42 > > > > [root@lpsdm52 ~]# mount -o remount,readahead=42 /net/spsdms/fs13 > > Bad nfs mount parameter: readahead > > [root@lpsdm52 ~]# mount -o readahead=42 /net/spsdms/fs13 > > Bad nfs mount parameter: readahead > > > > > > I assume the reply was meant to say that the correct way of introducing a > modifyable readahead size is to implement it as a mount option ? :-) > > Yes. > :-) > > I considered it, but it seems to be more intrusive than the workaround patch. > It also needs changes to userspace tools - correct? > > No. mount(8) will pass unrecognised options straight down into the > filesystem driver. > Has that always been the case, or is it a recent change? I have to support RHEL4 userland, which is not really new. > It's better this way - it allows the tunable to be set on a per-mount > basis rather than machine-wide. > No question about that. I just thought it to be to complicated. Maybe I erred. > Note that for block devices, readahead is a per-backing_dev_info thing > (and a backing_dev_info has a 1:1 relationship to a disk drive for sane > setups). > > And the NFS client maintains a backing_dev_info, which appears to map > onto a server, so making the NFS readahead a per-backing_dev_info (ie: > per server) thing might make sense. Maybe nfs makes per-server information > manipulatable down in sysfs somewhere.. I believe Peter wanted to add per bdi stuff for nfs some time ago. Not sure what came out of it. Cheers Martin