Huge Page

Ⅰ. Check Huge Page

  1. Linux 内核支持多种 page size。

    架构 HugePage Size
    arm64 4K, 2M and 1G (or 64K and 512M if one builds their own kernel with CONFIG_ARM64_64K_PAGES=y)
    x86 4K and 4M (2M in PAE mode,1GB if architecturally supported)
    amd64 2MB, 1GB
    ia64 4K, 8K, 64K, 256K, 1M, 4M, 16M, 256M
    ppc64 4K, 16M

  1. Huge Page 支持 mmapshmgetshmat 调用。

  2. 当前系统 Huge Page 设置信息

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    $ grep Huge /proc/meminfo 
    AnonHugePages: 0 kB
    ShmemHugePages: 0 kB
    HugePages_Total: 0
    HugePages_Free: 0
    HugePages_Rsvd: 0
    HugePages_Surp: 0
    Hugepagesize: 2048 kB
    Hugetlb: 0 kB
    • HugePages_Total Huge Page 池的页面数量。

    • HugePages_Free Huge Page 池中未分配的页面数量。

    • HugePages_Rsvd 已承诺从池中分配但尚未进行分配的 Huge Page 的数量。

    • HugePages_Surp /proc/sys/vm/nr_hugepages中 表示 Huge Page 池中页面数量。 /proc/sys/vm/nr_overcommit_hugepages 表示最大值。

    • Hugepagesize 默认 hugepage 尺寸(Kb)。

    • Hugetlb 内存总量(kB) HugePages_Total * Hugepagesize

  3. /proc/filesystems 可以查看 hugetlbfs 配置信息

  4. /proc/sys/vm/nr_hugepages 表示当前内核大页面池中“持久”大页面的数量。

  5. 检查 NUMA 系统中大型页面的每个节点分布情况,使用:

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    cat /sys/devices/system/node/node*/meminfo | fgrep Huge
  6. Shirink:

    Shrinking the persistent huge page pool via nr_hugepages such that it becomes less than the number of huge pages in use will convert the balance of the in-use huge pages to surplus huge pages. This will occur even if the number of surplus pages it would exceed the overcommit value. As long as this condition holds--that is, until nr_hugepages+nr_overcommit_hugepages is increased sufficiently, or the surplus huge pages go out of use and are freed -- no more surplus huge pages will be allowed to be allocated.

  7. 运行时 huge page 接口

    • /proc/sys/vm

    • /sys/kernel/mm/hugepageshugepages-${size}kB

Ⅱ、Huge Page 分配/释放与 NUMA 内存策略

分配或释放 huge page 可以使用:

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numactl -m <node-list> echo 20 >/proc/sys/vm/nr_hugepages_mempolicy

这个操作将会释放或分配 abs(20 - nr_hugepages)<node-list>

Ⅲ、使用 Huge Page

需要使用 mmap ,应该先挂载 hugetlbfs:

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 mount -t hugetlbfs \
-o uid=<value>,gid=<value>,mode=<value>,pagesize=<value>,size=<value>,\
min_size=<value>,nr_inodes=<value> none /mnt/huge

在内核 2.6 之后,可以使用 MAP_HUGETLB 的方式操作内存。

  • map_hugetlb

  • hugepage-shm

  • hugepage-mmaphttps://man7.org/linux/man-pages/man2/mmap.2.html

  • libhugetlbfs

测试

  • 设置 huge page

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    sysctl vm.nr_hugepages=192

    AnonHugePages: 0 kB
    ShmemHugePages: 0 kB
    HugePages_Total: 192
    HugePages_Free: 192
    HugePages_Rsvd: 0
    HugePages_Surp: 0
    Hugepagesize: 2048 kB
    Hugetlb: 393216 kB
  • huge.c 测试

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    #include <sys/mman.h>
    #include <stdio.h>
    #include <memory.h>

    int main(int argc, char *argv[]) {
    char *m;
    size_t s = (8UL * 1024 * 1024);

    m = mmap(NULL, s, PROT_READ | PROT_WRITE,
    MAP_PRIVATE | MAP_ANONYMOUS | 0x40000 /*MAP_HUGETLB*/, -1, 0);
    if (m == MAP_FAILED) {
    perror("map mem");
    m = NULL;
    return 1;
    }

    memset(m, 0, s);

    printf("map_hugetlb ok, press ENTER to quit!\n");
    getchar();

    munmap(m, s);
    return 0;
    }
  • 查看 huge page 信息

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    $ gcc huge.c
    $ ./a.out
    map_hugetlb ok, press ENTER to quit!

    $ cat /proc/meminfo |grep -i huge

    AnonHugePages: 0 kB
    ShmemHugePages: 0 kB
    HugePages_Total: 192
    HugePages_Free: 188
    HugePages_Rsvd: 0
    HugePages_Surp: 0
    Hugepagesize: 2048 kB
    Hugetlb: 393216 kB

Reference

  1. https://www.kernel.org/doc/Documentation/vm/hugetlbpage.txt

  2. http://blog.chinaunix.net/uid-28541347-id-5783934.html

  3. https://wiki.debian.org/Hugepages

  4. Linux下试验大页面映射(MAP_HUGETLB)_cncnlg的专栏-CSDN博客_map_hugetlb

  5. https://www.kernel.org/doc/Documentation/vm/transhuge.txt

  6. mmap(2) - Linux manual page

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