因此，malloc不调用任何系统调用吗? [英] So malloc doesn't invoke any syscall?

问题描述

相关代码:

  write(-1, "test", sizeof("test"));
  void * p = malloc(1024);
  void * p2 = malloc(510);
  write(-1, "hi", sizeof("hi"));

相关strace输出:

Related strace output:

write(4294967295, "test\0", 5)          = -1 EBADF (Bad file descriptor)
brk(0)                                  = 0x601000
brk(0x622000)                           = 0x622000
write(4294967295, "hi\0", 3)            = -1 EBADF (Bad file descriptor)

我很惊讶如此低级的操作不涉及系统调用?

I'm surprised such low level operation doesn't involve syscall?

推荐答案

并非每个对malloc的调用都调用一个syscall.在我的Linux桌面上，malloc以128KB的块分配一个空间，然后分配该空间.因此，每100-200个malloc调用我都会看到一个syscall.在freebsd上，malloc分配2MB的块.在您的计算机上，编号可能会有所不同.

Not every call to malloc invokes a syscall. On my linux desktop malloc allocates a space in 128KB blocks and then distributes the space. So I will see a syscall every 100-200 malloc calls. On freebsd malloc allocates by 2MB blocks. On your machine numbers will likely differ.

如果要在每个malloc上看到syscall，请分配大量内存(malloc(10 * 1024 * 1024 * 1024))

If you want to see syscall on every malloc allocate large amounts of memory (malloc(10*1024*1024*1024))

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