linux-kernel - Re: [PATCH] hugetlbfs: correct handling of negative input to /proc/sys/vm/nr

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Message-ID: <20110224182033.GA30387@mgebm.net>
Date:	Thu, 24 Feb 2011 13:20:33 -0500
From:	Eric B Munson <emunson@...bm.net>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Petr Holasek <pholasek@...hat.com>,
	linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Wu Fengguang <fengguang.wu@...el.com>, linux-mm@...ck.org
Subject: Re: [PATCH] hugetlbfs: correct handling of negative input to
 /proc/sys/vm/nr_hugepages

On Thu, 24 Feb 2011, Mel Gorman wrote:

> On Wed, Feb 23, 2011 at 04:18:18PM -0800, Andrew Morton wrote:
> > On Tue, 22 Feb 2011 10:02:36 +0000
> > Mel Gorman <mel@....ul.ie> wrote:
> > 
> > > On Mon, Feb 21, 2011 at 04:47:49PM +0100, Petr Holasek wrote:
> > > > When user insert negative value into /proc/sys/vm/nr_hugepages it will result
> > > > in the setting a random number of HugePages in system (can be easily showed
> > > > at /proc/meminfo output).
> > > 
> > > I bet you a shiny penny that the value of HugePages becomes the maximum
> > > number that could be allocated by the system at the time rather than a
> > > random value.
> > 
> > That seems to be the case from my reading.  In which case the patch
> > removes probably-undocumented and possibly-useful existing behavior.
> > 
> 
> It's not proof that no one does this but I'm not aware of any documentation
> related to hugetlbfs that recommends writing negative values to take advantage
> of this side-effect. It's more likely they simply wrote a very large number
> to nr_hugepages if they wanted "as many hugepages as possible" as it makes
> more intuitive sense than asking for a negative amount of pages. hugeadm at
> least is not depending on this behaviour AFAIK.

That is correct, hugeadm never writes negative values to huge page pool sizes.

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