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HugePageCornerCases

Corner cases are slightly non-obvious problems implementing huge pages. If you think of one, please archive it here so it doesn't come back and bite us later.

  • NUMA-aware allocation - don't want all the memory accesses going through one controller! See IBM's page about tuning Stream.

    • STREAM and hugetlb is a huge issue unless you have chipset level interleave no matter what

  • Fork of an application with huge pages when no huge pages are left - must fail over to small pages.

  • mmap of a file that is partially in cache already

  • mmap of a file that then gets replaced on disk

    • (say glibc text and then glibc gets upgraded to a newer version)

  • MAP_GROWSDOWN for stacks including automatic growth

  • mprotect to executable (scenario: dlopen of a shared lib that

    • requires executable stack, causing all thread stacks to be mprotected executable)

  • write() of mmaped area to the same file at an offset either

    • inside or outside the same 2Mb page

  • same but for an O_DIRECT write

  • same but for AIO write

  • sendfile() of a non-4Kb region

  • truncate of 4Mb mmaped file to 1Mb, then truncate to 1.5Mb

    • then 0.5Mb (creates a sparse file)

  • mmap of a 2Mb region in 2 parts: first 1Mb gets mmaped writable private,

    • second 2Mb gets mmaped shared writable; then write a few bytes to each part

  • Running a large .bss segment workload, specifying only a portion of the large page requirements to be made available to the workload... ie: app defines 10GB in arrays, but only 5GB are

  • whether an entire segment must be dedicated to huge pages (256MB in the ppc environment) if one huge page is specified Should huge pages be allocated by segment?

  • can we define stages of transparent functionality to enable customer production usage in the near future?

  • can a non-root userid be specified to have access to huge pages? in a production environment, admins may require ability to designate huge page users..

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last edited 2006-06-11 17:31:48 by ArjanVandeVen