std::bad_alloc异常，尽管有足够的可用内存

我的代码运行在64位Linux（openSUSE 13.1 x86_64）下，编译器是gcc（SUSE Linux）4.8.1。在程序执行的某个时刻，我得到了一个std:：bad_alloc异常，它源于std:：vector push_back调用。如gdb:所示

(gdb) bt
#0  0x00007ffff6053849 in raise () from /lib64/libc.so.6
#1  0x00007ffff6054cd8 in abort () from /lib64/libc.so.6
#2  0x00007ffff694c655 in __gnu_cxx::__verbose_terminate_handler() () from /usr/lib64/libstdc++.so.6
#3  0x00007ffff694a7c6 in ?? () from /usr/lib64/libstdc++.so.6
#4  0x00007ffff694a7f3 in std::terminate() () from /usr/lib64/libstdc++.so.6
#5  0x00007ffff694aa1e in __cxa_throw () from /usr/lib64/libstdc++.so.6
#6  0x00007ffff694af1d in operator new(unsigned long) () from /usr/lib64/libstdc++.so.6
#7  0x0000000000457ca6 in allocate (__n=8388608, this=0x7ffffffe1f80)
    at /usr/include/c++/4.8/ext/new_allocator.h:104
#8  _M_allocate (__n=8388608, this=0x7ffffffe1f80) at /usr/include/c++/4.8/bits/stl_vector.h:168
#9  std::vector<std::pair<long, long>, std::allocator<std::pair<long, long> > >::_M_insert_aux (
    this=this@entry=0x7ffffffe1f80, __position=..., __x=...) at /usr/include/c++/4.8/bits/vector.tcc:345
#10 0x000000000045335c in push_back (__x=..., this=0x7ffffffe1f80) at /usr/include/c++/4.8/bits/stl_vector.h:913
#11 c_RoutingNetzwerk::LoescheAktuelleKnoten (this=this@entry=0x7ffffffe2f30,
    aktuelle_knoten=std::vector of length 12803276, capacity 16777216 = {...}, ebene=ebene@entry=0,
    aktueller_kantengrad=std::vector of length 17266677, capacity 17266677 = {...}, algo=...,
    neue_abgehende_kanten=std::vector of length 4194304, capacity 4194304 = {...},
    neue_eingehende_kanten=std::vector of length 4194304, capacity 4194304 = {...})
    at RoutingAlgorithmus/RoutingNetzwerk.cpp:3275

对neue_abgehende_kanten.push_back（…）的调用使向量的大小加倍，所以我试图分配4194304*2*16字节=128 MB，但失败了。

另一方面，我有足够的内存（总共132GB），并且有足够的空闲内存（当我的程序在调试器中中断时拍摄的快照）：

m2883:~ # free -m
             total       used       free     shared    buffers     cached
Mem:        129151     128582        568          0         59      56334
-/+ buffers/cache:      72189      56962
Swap:         8195          5       8190

你知道为什么分配失败了吗？在我看来，系统似乎没有释放缓存供我的程序使用？！

我只是尝试了一个小实验，想出了

#include <cstdlib>
#include <stdio.h>
int main( int argc, char** argv)
{
    void* p = calloc( 1, 256 * 1024 * 1024 );
    if ( !p )
        printf( "failedn" );
    else
        printf( "all donen" );
}

这对于128兆字节仍然有效，但对于256兆字节则失败。

和：

m2883:~ # free -mh
             total       used       free     shared    buffers     cached
Mem:          126G       125G       593M         0B        60M        54G
-/+ buffers/cache:        70G        55G
Swap:         8.0G       5.4M       8.0G
transit@m2883:~/test> ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 1033140
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 1024
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 1033140
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

服务器似乎在某种程度上配置错误。即使在一个只运行几个系统服务的新启动系统上，我也不能分配超过70 GB的空间，我将其读取为64 GB+8 GB的交换空间。我已经联系了服务器管理员，并对这种情况进行了投诉。