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

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Message-ID: <20110224094912.GO15652@csn.ul.ie>
Date:	Thu, 24 Feb 2011 09:49:12 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	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 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.

-- 
Mel Gorman
SUSE Labs
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