Re: [PATCH] hugetlbfs: correct handling of negative input to/proc/sys/vm/nr_hugepages

From: Mel Gorman
Date: Thu Feb 24 2011 - 04:49:49 EST

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@xxxxxxxxx> 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
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