rshnn / memory-manager

Custom implementation of a heap memory allocator (malloc clone)

memory-manager

OUR STRUCTS

MEMENTRY

• segmented paging sort of
• 32 bits

struct memEntry{
    unsigned int    valid: 1;
    unsigned int    isfree:1;
    unsigned int    request_size:23;

    unsigned int    right_dependent:1; 

    unsigned int    UNUSED;6;
}

• bit fields
  • size (23bits) (maxes out at 8mb)
  • valid (1bit)
    • helps with freeing (cleaning up fragments)

PAGE TABLE ENTRY

• each thread has their own page table

• one page dedicated to ucontexts

• is a page resident in memory right now?

  • isloaded

• something about left dependent

struct page_table_entry{

    unsigned int    UNUSED:4;
    unsigned int    used:1;                  // Is the page currently used 
    unsigned int    resident:1;              // Is the page resident in memory 
    unsigned int    left_dependent:1;       // Do we need to load the next page
    unsigned int    right_dependent:1; 
    unsigned int    largest_available:12;   // Size of largest fragment availble inside the page
    unsigned int    page_number:12;         // Offset of page in memory (if it is loaded)

}

Still have 5 bits available! Defaulting mementry size to 32bits

Super Table Array

• One pointer per page_size chunk of page table entries
  • Size of array = 32 pointer entries

(struct page_table_entry*) super_table_array[32];

MEMORY

• 8MB
• a character array
• inside memory-manger's stack

char memory[8 million];          // char is 1 bytes.  Need 8MB

SWAP FILE

• 16MB
• file pointer

---

• begining of memory-manager.c
  • lseek(16MB)

What is going on here

#define SEG(type, base, lim, dpl) (struct segdesc)    \
{ ((lim) >> 12) & 0xffff, (uint)(base) & 0xffff,      \
  ((uint)(base) >> 16) & 0xff, type, 1, dpl, 1,       \
  (uint)(lim) >> 28, 0, 0, 1, 1, (uint)(base) >> 24 }
#define SEG16(type, base, lim, dpl) (struct segdesc)  \
{ (lim) & 0xffff, (uint)(base) & 0xffff,              \
  ((uint)(base) >> 16) & 0xff, type, 1, dpl, 1,       \
(uint)(lim) >> 16, 0, 0, 1, 0, (uint)(base) >> 24 }