无法通过move_pages()查询 [英] Fail to query via move_pages()

问题描述

#include <cstdint>
#include <iostream>
#include <numaif.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <limits>

int main(int argc, char** argv) {
    const constexpr uint64_t size = 16lu * 1024 * 1024;
    const constexpr uint32_t nPages = size / (4lu * 1024 * 1024);
    int32_t status[nPages];
    std::fill_n(status, nPages, std::numeric_limits<int32_t>::min());
    void* pages[nPages];

    auto fd = shm_open("test_shm", O_RDWR|O_CREAT, 0666);
    void* ptr = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);

    if (ptr == MAP_FAILED) {
        if (fd > 0) close(fd);
        throw "failed to map hugepages";
    }

    for (uint32_t i = 0; i < nPages; i++) {
        pages[i] = (char*)ptr + 4 * 1024 * 1024;
    }

    if (0 != move_pages(0, nPages, pages, nullptr, status, 0)) {
        std::cout << "failed to inquiry pages because " << strerror(errno) << std::endl;
    }
    else {
            for (uint32_t i = 0; i < nPages; i++) {
            std::cout << "page # " << i << " locates at numa node " << status[i] << std::endl;
        }
    }
    munmap(ptr, size);
    close(fd);
}

它会打印:

page # 0 locates at numa node -2
page # 1 locates at numa node -2
page # 2 locates at numa node -2
page # 3 locates at numa node -2

根据联机帮助页，其中指出:

nodes is an array of integers that specify the desired location for each page.
Each element in the array is a node number. nodes can also be NULL, in which 
case move_pages() does not move any pages but instead will return the node where 
each page currently resides, in the status array. Obtaining the status of each 
page may be necessary to determine pages that need to be moved.

为什么查询返回成功却打印负值?我的机器只有2个NUMA-0和1.

Why does it print negative values although querying return success? My machine only has 2 NUMAs -- 0 and 1.

内核版本:3.10.0-862.2.3.el7.x86_64

kernel version: 3.10.0-862.2.3.el7.x86_64

这是大页面的版本:

#include <cstdint>
#include <iostream>
#include <numaif.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <limits>

int main(int argc, char** argv) {
        const int32_t dst_node = strtoul(argv[1], nullptr, 10);
        const constexpr uint64_t size = 4lu * 1024 * 1024;
        const constexpr uint64_t pageSize = 2lu * 1024 * 1024;
        const constexpr uint32_t nPages = size / pageSize;
        int32_t status[nPages];
        std::fill_n(status, nPages, std::numeric_limits<int32_t>::min());
        void* pages[nPages];
        int32_t dst_nodes[nPages];
        void* ptr = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE | MAP_HUGETLB, -1, 0);

        if (ptr == MAP_FAILED) {
                throw "failed to map hugepages";
        }
        memset(ptr, 0x41, nPages*pageSize);
        for (uint32_t i = 0; i < nPages; i++) {
                pages[i] = &((char*)ptr)[i*pageSize];
                dst_nodes[i] = dst_node;
        }

        std::cout << "Before moving" << std::endl;

        if (0 != move_pages(0, nPages, pages, nullptr, status, 0)) {
            std::cout << "failed to inquiry pages because " << strerror(errno) << std::endl;
        }
        else {
                for (uint32_t i = 0; i < nPages; i++) {
                        std::cout << "page # " << i << " locates at numa node " << status[i] << std::endl;
                }
        }

        // real move
        if (0 != move_pages(0, nPages, pages, dst_nodes, status, MPOL_MF_MOVE_ALL)) {
                std::cout << "failed to move pages because " << strerror(errno) << std::endl;
                exit(-1);
        }

        const constexpr uint64_t smallPageSize = 4lu * 1024;
        const constexpr uint32_t nSmallPages = size / smallPageSize;
        void* smallPages[nSmallPages];
        int32_t smallStatus[nSmallPages] = {std::numeric_limits<int32_t>::min()};
        for (uint32_t i = 0; i < nSmallPages; i++) {
                smallPages[i] = &((char*)ptr)[i*smallPageSize];
        }


        std::cout << "after moving" << std::endl;
        if (0 != move_pages(0, nSmallPages, smallPages, nullptr, smallStatus, 0)) {
            std::cout << "failed to inquiry pages because " << strerror(errno) << std::endl;
        }
        else {
                for (uint32_t i = 0; i < nSmallPages; i++) {
                        std::cout << "page # " << i << " locates at numa node " << smallStatus[i] << std::endl;
                }
        }

}

有趣的是，move_pages()似乎可以理解大页面，因为在移动大页面后，我根据小页面尺寸进行查询，并填充了预期的NUMA ID.

The interesting thing is that move_pages() seems to understand hugepages as after the hugepages are moved, I query based on small page size, and it populates the expected NUMA IDs.

推荐答案

您对shm_open和mmap的使用可能不会获得所需的大页面.

Your usage of shm_open and mmap probably will not get huge pages as you want.

move_pages syscall(和libnuma包装器)在x86_64的4096字节标准页面上工作.

move_pages syscall (and libnuma wrapper) works on standard pages of 4096 bytes for x86_64.

然后您以错误的方式使用move_pages并使用了错误的第3个参数"pages".它不应该是指向内存的指针.但是指向本身将包含nPages指针的数组的指针:

And you use move_pages in wrong way with incorrect 3rd argument "pages". It should be not pointer to memory; but pointer to array which itself will contain nPages pointers:

http://man7.org/linux/man-pages/man2/move_pages.2.html

  long move_pages(int pid, unsigned long count, void **pages,
                   const int *nodes, int *status, int flags);

   pages is an array of pointers to the pages that should be moved.
   These are pointers that should be aligned to page boundaries.
   Addresses are specified as seen by the process specified by pid.

在页面"中没有正确的指针，根据errno 14(来自moreutils软件包)，您将得到-14，即EFAULT.

Without correct pointers in the "pages' you will get -14 which is EFAULT according to errno 14 (from moreutils package).

//https://stackoverflow.com/questions/54546367/fail-to-query-via-move-pages
//g++ 54546367.move_pages.cc -o 54546367.move_pages -lnuma -lrt
#include <cstdint>
#include <iostream>
#include <numaif.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <limits>

int main(int argc, char** argv) {
    const constexpr uint64_t size = 256lu * 1024;// * 1024;
    const constexpr uint32_t nPages = size / (4lu * 1024);
    void * pages[nPages];
    int32_t status[nPages];
    std::fill_n(status, nPages, std::numeric_limits<int32_t>::min());

//  auto fd = shm_open("test_shm", O_RDWR|O_CREAT, 0666);
//  void* ptr = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    void* ptr = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, 0, 0);
    std::cout << "Ptr is " << ptr << std::endl;
    if (ptr == MAP_FAILED) {
//      if (fd > 0) close(fd);
        throw "failed to map hugepages";
    }
    memset(ptr, 0x41, nPages*4096);
    for(uint32_t i = 0; i<nPages; i++) {
        pages[i] = &((char*)ptr)[i*4096];
    }

    if (0 != move_pages(0, nPages, pages, nullptr, status, 0)) {
        std::cout << "failed to inquiry pages because " << strerror(errno) << std::endl;
    }
    else {
        for (uint32_t i = 0; i < nPages; i++) {
            std::cout << "page # " << i << " locates at numa node " << status[i] << std::endl;
        }
    }
    munmap(ptr, size);
//  close(fd);
}

在NUMA机器上，它从taskset -c 7 ./54546367.move_pages启动时输出相同的节点，而在numactl -i all ./54546367.move_pages时交错输出(0 1 0 1).

With NUMA machine it outputs same node when started as taskset -c 7 ./54546367.move_pages and interleaved (0 1 0 1) when numactl -i all ./54546367.move_pages.

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