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Date: Wed, 21 Mar 2007 16:11:40 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Randy Dunlap <randy.dunlap@oracle.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>, "J.H." <warthog9@kernel.org>,
       kernel list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] sysctl: vfs_cache_divisor
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On Wed, 21 Mar 2007 16:01:32 -0700
Randy Dunlap <randy.dunlap@oracle.com> wrote:

> On Mon, 19 Mar 2007 21:22:33 -0700 H. Peter Anvin wrote:
> 
> > Randy Dunlap wrote:
> > >>
> > >> The we duplicate all the relevant /proc knobs:
> > >>
> > >> cat /proc/sys/vm/dirty_ratio
> > >> 30
> > >> cat /proc/sys/vm/hires-dirty_ratio/
> > >> 300000
> > >>
> > >> Or we do something else ;)
> > > 
> > > Sounds better.  I wasn't very keen on the userspace interface that this
> > > exposed.  Will look at those.
> > > 
> > 
> > Okay... may be I could throw a spanner in the machinery, and suggest 
> > another option: perhaps we should add a way to do sysctl which can 
> > handle fractional (fixed-point) values... more coherent/detailed message 
> > tomorrow.
> 
> I prefer the fixed-point values for pressure and dirty* to having
> duplicated entries for each of them.  I'll proceed with that idea.
> 

Problem is, if a read of /proc/sys/vm/dirty_ratio is changed to return
7.457 then existing userspace might get confused.

This might be acceptable if we are careful to ensure that reads of
/proc/sys/vm/dirty_ratio will always return an integer if it was previously
initialised with an integer.