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    SubjectRe: [RFC PATCH 2/4] hugetlb: add support for preferred node to alloc_huge_page_nodemask
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    On 06/14/2017 03:12 PM, Mike Kravetz wrote:
    > On 06/13/2017 02:00 AM, Michal Hocko wrote:
    >> From: Michal Hocko <mhocko@suse.com>
    >>
    >> alloc_huge_page_nodemask tries to allocate from any numa node in the
    >> allowed node mask starting from lower numa nodes. This might lead to
    >> filling up those low NUMA nodes while others are not used. We can reduce
    >> this risk by introducing a concept of the preferred node similar to what
    >> we have in the regular page allocator. We will start allocating from the
    >> preferred nid and then iterate over all allowed nodes in the zonelist
    >> order until we try them all.
    >>
    >> This is mimicking the page allocator logic except it operates on
    >> per-node mempools. dequeue_huge_page_vma already does this so distill
    >> the zonelist logic into a more generic dequeue_huge_page_nodemask
    >> and use it in alloc_huge_page_nodemask.
    >>
    >> Signed-off-by: Michal Hocko <mhocko@suse.com>
    >> ---
    >
    >
    > I built attempts/hugetlb-zonelists, threw it on a test machine, ran the
    > libhugetlbfs test suite and saw failures. The failures started with this
    > patch: commit 7e8b09f14495 in your tree. I have not yet started to look
    > into the failures. It is even possible that the tests are making bad
    > assumptions, but there certainly appears to be changes in behavior visible
    > to the application(s).

    nm. The failures were the result of dequeue_huge_page_nodemask() always
    returning NULL. Vlastimil already noticed this issue and provided a
    solution.

    --
    Mike Kravetz

    >
    > FYI - My 'test machine' is an x86 KVM insatnce with 8GB memory simulating
    > 2 nodes. Huge page allocations before running tests:
    > node0
    > 512 free_hugepages
    > 512 nr_hugepages
    > 0 surplus_hugepages
    > node1
    > 512 free_hugepages
    > 512 nr_hugepages
    > 0 surplus_hugepages
    >
    > I can take a closer look at the failures tomorrow.
    >

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