Linux：由于虚拟内存限制，在单个进程中分配的内存不能超过32 GB/64 GB

Question

#include <stdlib.h>
#include <iostream>

int main()
{
   size_t gb_in_bytes = size_t(1)<<size_t(30); // 1 GB in bytes (2^30).
   // try to allocate 1 block of 'i' GB.
   for (size_t i = 25; i < 35; ++ i) {
      size_t n = i * gb_in_bytes;
      void *p = ::malloc(n);
      std::cout << "allocation of 1 x " << (n/double(gb_in_bytes)) << " GB of data. Ok? " << ((p==0)? "nope" : "yes") << std::endl;
      ::free(p);
   }
}

/tmp> c++ mem_alloc.cpp && a.out

allocation of 1 x 25 GB of data. Ok? yes
allocation of 1 x 26 GB of data. Ok? yes
allocation of 1 x 27 GB of data. Ok? yes
allocation of 1 x 28 GB of data. Ok? yes
allocation of 1 x 29 GB of data. Ok? yes
allocation of 1 x 30 GB of data. Ok? yes
allocation of 1 x 31 GB of data. Ok? nope
allocation of 1 x 32 GB of data. Ok? nope
allocation of 1 x 33 GB of data. Ok? nope
allocation of 1 x 34 GB of data. Ok? nope

~> ulimit -all
[...]
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
virtual memory          (kbytes, -v) 32505856
[...]

~> ulimit -v 64000000
~> ulimit -v 65000000                                                                                                                                  
bash: ulimit: virtual memory: cannot modify limit: Operation not permitted                                                                              
~> ulimit -v unlimited
bash: ulimit: virtual memory: cannot modify limit: Operation not permitted 

编辑：

>

继Ingo Leonhardt之后，我在以root用户身份而不是以标准用户身份登录后尝试了ulimits-v unlimited。这样做解决了root的问题（然后程序可以在以root身份登录时分配所有物理内存）。但这只适用于root用户，不适用于其他用户。但是，至少这意味着原则上内核可以很好地处理这一点，而且只有一个配置问题。

关于limits.conf:我尝试显式地添加

null

>

这是我自己的愚蠢造成的。在我的用户设置中有一个（早已被遗忘的）程序，它使用setrlimit来限制每个进程的内存量，以防止Linux的死机交换。它无意中从32 GB的计算机复制到128 GB的计算机。感谢Paul和Andrew Janke以及其他所有帮助找到它的人。对不起大家：/。

如果其他人遇到这种情况：在bash和profile设置中搜索ulimit/setrlimit，以及可能调用这些设置的程序（包括您自己的和系统范围的/etc设置），并确保/security/limits.conf不包括此限制...（或者至少尝试创建一个新用户，看看这是否发生在您的用户或系统设置中）

Answer 1

这是ulimit和系统设置问题，而不是C++问题。

我可以在Amazon EC2实例类型r3.4xlarege上运行适当修改过的代码。这些在现货市场上的价格不到0.20美元/小时，所以我建议你租一个，也许可以在/etc中看看，并与你自己的设置进行比较...或者您需要重新编译Linux内核才能使用这么多内存...但这不是C++或gcc的问题。

EC2机器上的Ubuntu已经设置为无限进程内存。

$ sudo su
# ulimit -u
--> unlimited

# free
             total       used       free     shared    buffers     cached
Mem:     125903992    1371828  124532164        344      22156     502248
-/+ buffers/cache:     847424  125056568
Swap:            0          0          0

我修改了您的程序的限制，以提高到149GB。

这是输出结果。高达118GB看起来不错。

root@ip-10-203-193-204:/home/ubuntu# ./memtest
allocation of 1 x 25 GB of data. Ok? yes
allocation of 1 x 26 GB of data. Ok? yes
allocation of 1 x 27 GB of data. Ok? yes
allocation of 1 x 28 GB of data. Ok? yes
allocation of 1 x 29 GB of data. Ok? yes
allocation of 1 x 30 GB of data. Ok? yes
allocation of 1 x 31 GB of data. Ok? yes
allocation of 1 x 32 GB of data. Ok? yes
allocation of 1 x 33 GB of data. Ok? yes
allocation of 1 x 34 GB of data. Ok? yes
allocation of 1 x 35 GB of data. Ok? yes
allocation of 1 x 36 GB of data. Ok? yes
allocation of 1 x 37 GB of data. Ok? yes
allocation of 1 x 38 GB of data. Ok? yes
allocation of 1 x 39 GB of data. Ok? yes
allocation of 1 x 40 GB of data. Ok? yes
allocation of 1 x 41 GB of data. Ok? yes
allocation of 1 x 42 GB of data. Ok? yes
allocation of 1 x 43 GB of data. Ok? yes
allocation of 1 x 44 GB of data. Ok? yes
allocation of 1 x 45 GB of data. Ok? yes
allocation of 1 x 46 GB of data. Ok? yes
allocation of 1 x 47 GB of data. Ok? yes
allocation of 1 x 48 GB of data. Ok? yes
allocation of 1 x 49 GB of data. Ok? yes
allocation of 1 x 50 GB of data. Ok? yes
allocation of 1 x 51 GB of data. Ok? yes
allocation of 1 x 52 GB of data. Ok? yes
allocation of 1 x 53 GB of data. Ok? yes
allocation of 1 x 54 GB of data. Ok? yes
allocation of 1 x 55 GB of data. Ok? yes
allocation of 1 x 56 GB of data. Ok? yes
allocation of 1 x 57 GB of data. Ok? yes
allocation of 1 x 58 GB of data. Ok? yes
allocation of 1 x 59 GB of data. Ok? yes
allocation of 1 x 60 GB of data. Ok? yes
allocation of 1 x 61 GB of data. Ok? yes
allocation of 1 x 62 GB of data. Ok? yes
allocation of 1 x 63 GB of data. Ok? yes
allocation of 1 x 64 GB of data. Ok? yes
allocation of 1 x 65 GB of data. Ok? yes
allocation of 1 x 66 GB of data. Ok? yes
allocation of 1 x 67 GB of data. Ok? yes
allocation of 1 x 68 GB of data. Ok? yes
allocation of 1 x 69 GB of data. Ok? yes
allocation of 1 x 70 GB of data. Ok? yes
allocation of 1 x 71 GB of data. Ok? yes
allocation of 1 x 72 GB of data. Ok? yes
allocation of 1 x 73 GB of data. Ok? yes
allocation of 1 x 74 GB of data. Ok? yes
allocation of 1 x 75 GB of data. Ok? yes
allocation of 1 x 76 GB of data. Ok? yes
allocation of 1 x 77 GB of data. Ok? yes
allocation of 1 x 78 GB of data. Ok? yes
allocation of 1 x 79 GB of data. Ok? yes
allocation of 1 x 80 GB of data. Ok? yes
allocation of 1 x 81 GB of data. Ok? yes
allocation of 1 x 82 GB of data. Ok? yes
allocation of 1 x 83 GB of data. Ok? yes
allocation of 1 x 84 GB of data. Ok? yes
allocation of 1 x 85 GB of data. Ok? yes
allocation of 1 x 86 GB of data. Ok? yes
allocation of 1 x 87 GB of data. Ok? yes
allocation of 1 x 88 GB of data. Ok? yes
allocation of 1 x 89 GB of data. Ok? yes
allocation of 1 x 90 GB of data. Ok? yes
allocation of 1 x 91 GB of data. Ok? yes
allocation of 1 x 92 GB of data. Ok? yes
allocation of 1 x 93 GB of data. Ok? yes
allocation of 1 x 94 GB of data. Ok? yes
allocation of 1 x 95 GB of data. Ok? yes
allocation of 1 x 96 GB of data. Ok? yes
allocation of 1 x 97 GB of data. Ok? yes
allocation of 1 x 98 GB of data. Ok? yes
allocation of 1 x 99 GB of data. Ok? yes
allocation of 1 x 100 GB of data. Ok? yes
allocation of 1 x 101 GB of data. Ok? yes
allocation of 1 x 102 GB of data. Ok? yes
allocation of 1 x 103 GB of data. Ok? yes
allocation of 1 x 104 GB of data. Ok? yes
allocation of 1 x 105 GB of data. Ok? yes
allocation of 1 x 106 GB of data. Ok? yes
allocation of 1 x 107 GB of data. Ok? yes
allocation of 1 x 108 GB of data. Ok? yes
allocation of 1 x 109 GB of data. Ok? yes
allocation of 1 x 110 GB of data. Ok? yes
allocation of 1 x 111 GB of data. Ok? yes
allocation of 1 x 112 GB of data. Ok? yes
allocation of 1 x 113 GB of data. Ok? yes
allocation of 1 x 114 GB of data. Ok? yes
allocation of 1 x 115 GB of data. Ok? yes
allocation of 1 x 116 GB of data. Ok? yes
allocation of 1 x 117 GB of data. Ok? yes
allocation of 1 x 118 GB of data. Ok? yes
allocation of 1 x 119 GB of data. Ok? nope
allocation of 1 x 120 GB of data. Ok? nope
allocation of 1 x 121 GB of data. Ok? nope
allocation of 1 x 122 GB of data. Ok? nope
allocation of 1 x 123 GB of data. Ok? nope
allocation of 1 x 124 GB of data. Ok? nope
allocation of 1 x 125 GB of data. Ok? nope
allocation of 1 x 126 GB of data. Ok? nope
allocation of 1 x 127 GB of data. Ok? nope
allocation of 1 x 128 GB of data. Ok? nope
allocation of 1 x 129 GB of data. Ok? nope
allocation of 1 x 130 GB of data. Ok? nope
allocation of 1 x 131 GB of data. Ok? nope
allocation of 1 x 132 GB of data. Ok? nope
allocation of 1 x 133 GB of data. Ok? nope
allocation of 1 x 134 GB of data. Ok? nope
allocation of 1 x 135 GB of data. Ok? nope
allocation of 1 x 136 GB of data. Ok? nope
allocation of 1 x 137 GB of data. Ok? nope
allocation of 1 x 138 GB of data. Ok? nope
allocation of 1 x 139 GB of data. Ok? nope
allocation of 1 x 140 GB of data. Ok? nope
allocation of 1 x 141 GB of data. Ok? nope
allocation of 1 x 142 GB of data. Ok? nope
allocation of 1 x 143 GB of data. Ok? nope
allocation of 1 x 144 GB of data. Ok? nope
allocation of 1 x 145 GB of data. Ok? nope
allocation of 1 x 146 GB of data. Ok? nope
allocation of 1 x 147 GB of data. Ok? nope
allocation of 1 x 148 GB of data. Ok? nope
allocation of 1 x 149 GB of data. Ok? nope

现在，我在这个上面花了0.17美元的美国...