Malloc and space Configurator

malloc Principle ：

1.malloc Start searching for free space , If you can find a suitable space, allocate it
2. If it cannot be found, call the system call brk Get more free space from the heap （ With 128 For boundaries ,brk or mmap）
3. call brk Then turn to the kernel state , At this time, the virtual address system starts to work , Expand the heap area of the process （ No more physical memory allocated ）
4.brk Return to malloc,malloc Find the right space and return （ Switch from kernel mode to user mode ）
5. Process gets resources , Continue to work
6. When there is code to read and write the newly applied memory, there is a page missing interrupt , At this time, switch from user mode to kernel mode , The operating system allocates physical memory at this time , Switch back to , The program continues .

Space configurator

STL-SGI Use a two-level space configurator to ensure the rational application of heap resources , exceed 128types Use of and space configurator , lower than 128 Byte use secondary space configurator , The following is the specific allocation process of the secondary space configurator