On Thu, Feb 24, 2011 at 02:13:35PM -0800, Andrew Morton wrote:

On Thu, 24 Feb 2011 14:10:34 -0800
Andrew Morton [off-list ref] wrote:

quoted

On Tue, 22 Feb 2011 21:17:04 +0100
Petr Holasek [off-list ref] wrote:

quoted

When user insert negative value into /proc/sys/vm/nr_hugepages it will 
result
in the setting a random number of HugePages in system

Is this true?  afacit the kernel will allocate as many pages as it can
and will then set /proc/sys/vm/nr_hugepages to reflect the result. 
That's not random.

Assuming the above to be correct, I altered the changelog thusly:

AFAIK, it's correct.

: When the user inserts a negative value into /proc/sys/vm/nr_hugepages it
: will cause the kernel to allocate as many hugepages as possible and to
: then update /proc/meminfo to reflect this.
:
: This changes the behavior so that the negative input will result in
: nr_hugepages value being unchanged.

and given that, I don't really see why we should change the existing behaviour.

The main motivation is that asking the kernel for -1 pages and getting a
sensible response just feels wrong. The second reason I'd guess is that an
administrator script that was buggy (or raced with a second) instance that
accidentally wrote a negative number to the proc interface would try allocating
all memory as huge pages instead of reducing the number of hugepages as
was probably intended. Totally hypothetical case of course, I haven't
actually heard of this happening to anyone.

-- 
Mel Gorman
SUSE Labs

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