Demo: malloc() Under strace

The same 4 MB as one malloc() and as 1024 small ones, with strace counting.

Run

make
strace -e trace=brk,mmap,munmap ./malloc_size_entire 1024
strace -c -e trace=brk,mmap,munmap ./malloc_size_pages 1024

Ask

• One malloc(), one mmap() of 4,198,400 bytes. Where did the extra 4 KB come from?
• 1024 malloc()s, 35 brk()s. What is the allocator doing between system calls?
• Neither trace says how much of the 4 MB is in physical memory. What would?