Subject: Re: per BDI dirty limit (was Re: -mm merge plans for 2.6.24)
From: Kay Sievers <kay.sievers@vrfy.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>,
       Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
       Jens Axboe <jens.axboe@oracle.com>,
       Fengguang Wu <fengguang.wu@gmail.com>, greg@kroah.com
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	 <200710022205.05295.nickpiggin@yahoo.com.au>
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Date: Wed, 03 Oct 2007 15:35:25 +0200
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On Wed, 2007-10-03 at 12:37 +0200, Peter Zijlstra wrote:
> On Wed, 2007-10-03 at 12:15 +0200, Kay Sievers wrote:
> > On Tue, 2007-10-02 at 22:05 +1000, Nick Piggin wrote:
> > > On Tuesday 02 October 2007 21:40, Peter Zijlstra wrote:
> > > > On Tue, 2007-10-02 at 13:21 +0200, Kay Sievers wrote:
> > > 
> > > > > How about adding this information to the tree then, instead of
> > > > > creating a new top-level hack, just because something that you think
> > > > > you need doesn't exist.
> > > >
> > > > So you suggest adding all the various network filesystems in there
> > > > (where?), and adding the concept of a BDI, and ensuring all are properly
> > > > linked together - somehow. Feel free to do so.
> > > 
> > > Would something fit better under /sys/fs/? At least filesystems are
> > > already an existing concept to userspace.
> > 
> > Sounds at least less messy than an new top-level directory.
> > 
> > But again, if it's "device" releated, like the name suggests, it should
> > be reachable from the device tree.
> > Which userspace tool is supposed to set these values, and at what time?
> > An init-script, something at device discovery/setup? If that is is ever
> > going to be used in a hotplug setup, you really don't want to go look
> > for directories with magic device names in another disconnected tree.
> 
> Filesystems don't really map to BDIs either. One can have multiple FSs
> per BDI.
> 
> 'Normally' a BDI relates to a block device, but networked (and other
> non-block device) filesystems have to create a BDI too. So these need to
> be represented some place as well.
> 
> The typical usage would indeed be init scripts. The typical example
> would be setting the read-ahead window. Currently that cannot be done
> for NFS mounts.

What kind of context for a non-block based fs will get the bdi controls
added? Is there a generic place, or does every non-block based
filesystem needs to be adapted individually to use it?

Kay

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