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    SubjectRe: [PATCH v2 4/4] mm/vmalloc: Hugepage vmalloc mappings
    On Mon, Apr 13, 2020 at 10:53:03PM +1000, Nicholas Piggin wrote:
    > For platforms that define HAVE_ARCH_HUGE_VMAP and support PMD vmap mappings,
    > have vmalloc attempt to allocate PMD-sized pages first, before falling back
    > to small pages. Allocations which use something other than PAGE_KERNEL
    > protections are not permitted to use huge pages yet, not all callers expect
    > this (e.g., module allocations vs strict module rwx).
    >
    > This gives a 6x reduction in dTLB misses for a `git diff` (of linux), from
    > 45600 to 6500 and a 2.2% reduction in cycles on a 2-node POWER9.
    >
    > This can result in more internal fragmentation and memory overhead for a
    > given allocation. It can also cause greater NUMA unbalance on hashdist
    > allocations.
    >
    > There may be other callers that expect small pages under vmalloc but use
    > PAGE_KERNEL, I'm not sure if it's feasible to catch them all. An
    > alternative would be a new function or flag which enables large mappings,
    > and use that in callers.

    Why do we even use vmalloc in this case rather than just doing a huge
    page allocation? What callers are you intersted in?

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