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    SubjectRe: [RFC PATCH 2/2] arm64: Implement vmalloc based thread_info allocator
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    On Monday 25 May 2015 01:02:20 Jungseok Lee wrote:
    > Fork-routine sometimes fails to get a physically contiguous region for
    > thread_info on 4KB page system although free memory is enough. That is,
    > a physically contiguous region, which is currently 16KB, is not available
    > since system memory is fragmented.
    >
    > This patch tries to solve the problem as allocating thread_info memory
    > from vmalloc space, not 1:1 mapping one. The downside is one additional
    > page allocation in case of vmalloc. However, vmalloc space is large enough,
    > around 240GB, under a combination of 39-bit VA and 4KB page. Thus, it is
    > not a big tradeoff for fork-routine service.

    vmalloc has a rather large runtime cost. I'd argue that failing to allocate
    thread_info structures means something has gone very wrong.

    Can you describe the scenario that leads to fragmentation this bad?

    Could the stack size be reduced to 8KB perhaps?

    Arnd


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