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    SubjectRe: [PATCH v2] hugetlbfs: correct handling of negative input to /proc/sys/vm/nr_hugepages
    On Thu, Feb 24, 2011 at 02:13:35PM -0800, Andrew Morton wrote:
    > On Thu, 24 Feb 2011 14:10:34 -0800
    > Andrew Morton <akpm@linux-foundation.org> wrote:
    >
    > > On Tue, 22 Feb 2011 21:17:04 +0100
    > > Petr Holasek <pholasek@redhat.com> 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
    > >
    > > 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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