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

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Message-ID: <1605509214.19935074.1383821028439.JavaMail.root@redhat.com>
Date:	Thu, 7 Nov 2013 05:43:48 -0500 (EST)
From:	Jerome Marchand <jmarchan@...hat.com>
To:	Dave Hansen <dave.hansen@...el.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] mm: allow to set overcommit ratio more precisely



----- Original Message -----
> From: "Dave Hansen" <dave.hansen@...el.com>
> To: "Andrew Morton" <akpm@...ux-foundation.org>, "Jerome Marchand" <jmarchan@...hat.com>
> Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org
> 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@...hat.com> 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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