dshlyuger / freelistmalloc Goto Github PK

Main file to look at is mm.c

To see this malloc implementation work in a trace run make and then ./mdriver(driver and test code was provided by class staff)

This file contains an implementation of the malloc method in C which when given
a size, fetches a free and approrpriate block of memory to the requester for
use. It also includes the related methods realloc, which takes an existing
block and expands it to be of at least the given size, calloc which mallocs
with instantiated 0s, and free, which frees a particular block of memory and is
used in malloc itself.

The goal of this malloc implementation is not only to give an apporpriate
block of memory to the user, but to do so quickly and without demanding to much
memory from the heap that isn't needed.

In general free blocks are organized into segregated free lists, seperate lists
which contain blocks who's size falls into a particular range. In this
implementation, If a particular free list is empty the pointer to the
head of that freelist points to the prologue and if a particular block is
the last block in it's free list it's next pointer also points to the prologue.

On a high level, when a user wants to malloc a particular block of memory, the
program checks to see if a free block exsists in the free list that best
corresponds to the size requested it picks roughly the first one it encounters 
looking ahead a set amount first to see if any following block is a better fit. 
If such a block does not exsist in that particular freelist the program looks 
in other buckets with free blocks large enough to accomdate the request, 
adding back any aligned excess memory back into the freelist whenever 
a block is found.

If such a freeblock does not exist the program requests additional memory
for the heap of a particular chunksize coalesces it with any neighboring
free memory, returns the block to the user, and
again adds back any excess aligned memory back into the approprirate free list.

When a user decides to free a particulular block the program marks the block
as unallocated, coalesces it with any adjacent free blocks and adds it to the
approrpriate freelist.