我有一台带有128 GB RAM的计算机，运行Linux（3.19.5-200.fc21.x86_64）。但是，我不能在一个过程中分配超过30 GB的RAM。除此之外，malloc失败：
#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);
}
}
这会产生以下输出：
/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
我搜索了一段时间，发现这与最大虚拟内存大小有关：
~> ulimit -all
[...]
max locked memory (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
virtual memory (kbytes, -v) 32505856
[...]
我可以通过ulimit -v 64000000将此限制增加到〜64 GB，但不进一步。除此之外，我得到了operation not permitted错误：
~> 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
更多的搜索表明，原则上应该可以通过/etc/security/limits.conf中的" AS"（地址空间）条目设置这些限制。但是，通过这样做，我只能减少最大虚拟内存量，而不是增加增加 it。
是否有任何方法可以完全提高每个过程的虚拟内存限制，或者将其增加超过64 GB？我想在一个应用程序中使用所有物理内存。
编辑：
在Ingo Leonhardt之后，我尝试了
ulimits -v unlimited登录为root，而不是标准用户。这样做可以解决root的问题（然后程序可以在登录为root时分配所有物理内存）。但这仅适用于root，而不适用于其他用户。但是，至少这意味着原则上，内核可以很好地处理它，并且只有一个配置问题。关于
limits.conf：我尝试明确添加- 难以无限
- 柔软为无限
到
/etc/security/limits.conf，然后重新启动。这没有效果。作为标准用户登录后，ulimit -v仍然返回约32 GB，ulimit -v 65000000仍表示permission denied（而ulimit -v 64000000工作起作用）。limits.conf的其余部分被评论出来，在/etc/security/limits.d中，只有一个无关的条目（对于非根本用户，将nproc至4096限制为4096）。也就是说，虚拟内存限制必须来自limits.conf以外的其他地方。还有什么想法会导致ulimits -v不被"无限"？
编辑/分辨率：
这是由我自己的愚蠢引起的。我的用户设置中有一个（长期遗忘的）程序，该程序使用
setrlimit限制每个过程的内存量，以防止Linux交换为死亡。它是从32 GB机器到128 GB机器的无意中复制的。感谢Paul和Andrew Janke以及其他所有人都帮助了它。对不起，大家：/。如果其他人遇到以下内容：在bash和个人资料设置中搜索
ulimit/setrlimit，并且程序可能会拨打这些限制（您自己和系统范围/范围的设置），并确保/security/limits.conf不包括此限制...（或至少尝试创建新用户，以查看您的用户或系统设置中是否发生这种情况）
这是一个ULIMIT和系统设置问题，而不是C 问题。
我可以在Amazon EC2实例类型r3.4xlarge上运行您的适当修改的代码，毫无问题。这些在现货市场上的价格不到$ 0.20/小时，所以我建议您租一个，也许在/etc中浏览并与您自己的设置进行比较...或者也许您需要重新编译Linux内核来使用它内存很多...但这不是C 或GCC问题。
Ubuntu已经为无限的过程内存设置了。
$ sudo su
# ulimit -u
--> unlimited
这个有125GB的RAM
# 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至149GB。
这是输出。看起来不错至118GB。
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，我花了大约0.17美元...