为什么mmap（）的失败，一个1TB稀疏文件ENOMEM？ [英] Why does mmap() fail with ENOMEM on a 1TB sparse file?

问题描述

我一直与在openSUSE 11.2 x86_64的大稀疏文件。当我尝试mmap（）的1TB的稀疏文件时，出现ENOMEM。我本来以为64位地址空间就足够了TB级映射，但似乎并非如此。进一步的实验，一个1GB的文件工作正常，但一个2GB的文件（还有更大的）失败。我猜有可能是一个地方的设置来调整，而是一个广泛的搜索变成了什么。

下面是一些示例code，显示问题 - 任何线索

 的#include＆LT;＆errno.h中GT;
＃包括LT＆;＆fcntl.h GT;
＃包括LT＆;＆stdio.h中GT;
＃包括LT＆;＆stdlib.h中GT;
＃包括LT＆;＆string.h中GT;
＃包括LT＆; SYS / mman.h＆GT;
＃包括LT＆; SYS / types.h中＆GT;
＃包括LT＆;＆unistd.h中GT;INT主（INT ARGC，CHAR *的argv []）{
    字符*文件名=的argv [1];
    INT的fd;
    off_t大小= 1UL＆L​​T;＆LT; 40; // 30 == 1GB，40 1TB = =    FD =开放（文件名，O_RDWR | O_CREAT | O_TRUNC，0666）;
    ftruncate（FD，大小）;
    的printf（创建％ld个字节的稀疏文件\\ n，大小）;    字符*缓冲=（字符*）MMAP（NULL，（为size_t）大小，PROT_READ | PROT_WRITE，MAP_SHARED，FD，0）;
    如果（缓冲== MAP_FAILED）{
        PERROR（MMAP）;
        出口（1）;
    }
    的printf（完成MMAP  - 返回为0x0％LX \\ n，（无符号长）缓冲区）;    的strcpy（缓冲器cafebabe）;
    的printf（中写道启动\\ n）;    的strcpy（缓冲液+（大小 -  9），DEADBEEF）;
    的printf（中写道结束\\ n）;    如果（在munmap（缓冲液，（为size_t）大小）小于0）{
        PERROR（则munmap）;
        出口（1）;
    }
    关闭（FD）;    返回0;
}
 

解决方案

的问题是，每个进程的虚拟内存限制设置为仅1.7GB。 的ulimit -v 1610612736 将其设置为1.5TB和我的mmap（）的调用成功。谢谢， bmargulies ，对于提示尝试的ulimit -a！

I've been working with large sparse files on openSUSE 11.2 x86_64. When I try to mmap() a 1TB sparse file, it fails with ENOMEM. I would have thought that the 64 bit address space would be adequate to map in a terabyte, but it seems not. Experimenting further, a 1GB file works fine, but a 2GB file (and anything bigger) fails. I'm guessing there might be a setting somewhere to tweak, but an extensive search turns up nothing.

Here's some sample code that shows the problem - any clues?

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <unistd.h>

int main(int argc, char *argv[]) {
    char * filename = argv[1];
    int fd;
    off_t size = 1UL << 40; // 30 == 1GB, 40 == 1TB

    fd = open(filename, O_RDWR | O_CREAT | O_TRUNC, 0666);
    ftruncate(fd, size);
    printf("Created %ld byte sparse file\n", size);

    char * buffer = (char *)mmap(NULL, (size_t)size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    if ( buffer == MAP_FAILED ) {
        perror("mmap");
        exit(1);
    }
    printf("Done mmap - returned 0x0%lx\n", (unsigned long)buffer);

    strcpy( buffer, "cafebabe" );
    printf("Wrote to start\n");

    strcpy( buffer + (size - 9), "deadbeef" );
    printf("Wrote to end\n");

    if ( munmap(buffer, (size_t)size) < 0 ) {
        perror("munmap");
        exit(1);
    }
    close(fd);

    return 0;
}

解决方案

The problem was that the per-process virtual memory limit was set to only 1.7GB. ulimit -v 1610612736 set it to 1.5TB and my mmap() call succeeded. Thanks, bmargulies, for the hint to try ulimit -a!

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