Re: [PATCH v4 2/2] mm: allow to set overcommit ratio more precisely

From: Jerome Marchand
Date: Thu Nov 07 2013 - 05:44:15 EST

----- Original Message -----
> From: "Dave Hansen" <dave.hansen@xxxxxxxxx>
> To: "Andrew Morton" <akpm@xxxxxxxxxxxxxxxxxxxx>, "Jerome Marchand" <jmarchan@xxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx
> Sent: Thursday, November 7, 2013 12:49:54 AM
> Subject: Re: [PATCH v4 2/2] mm: allow to set overcommit ratio more precisely
> On 11/06/2013 02:33 PM, Andrew Morton wrote:
> > On Wed, 6 Nov 2013 03:42:20 -0500 (EST) Jerome Marchand
> > <jmarchan@xxxxxxxxxx> wrote:
> >> That was my first version of this patch (actually "kbytes" to avoid
> >> overflow).
> >> Dave raised the issue that it silently breaks the user interface:
> >> overcommit_ratio is zero while the system behaves differently.
> >
> > I don't understand that at all. We keep overcommit_ratio as-is, with
> > the same default values and add a different way of altering it. That
> > should be back-compatible?
> Reading the old thread, I think my main point was that we shouldn't
> output overcommit_ratio=0 when overcommit_bytes>0. We need to round up
> for numbers less than 1 so that folks don't think overcommit_ratio is _off_.

This is not how current *bytes work. Also the *ratio and *bytes value
would diverge if the amount of memory changes (e.g. memory hotplug).

> I was really just trying to talk you in to cramming the extra precision
> in to the _existing_ sysctl. :) I don't think bytes vs. ratio is really
> that big of a deal.

If everybody agrees on overcommit_kbytes, I can resend my original patch.
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