Dynamic Memory Allocation: Understanding Heap Management in Operating Systems - Prof. Mich, Study notes of Computer Science

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CS 351 : Saelee

Dynamic Memory

Allocation

Disk Virtual Memory 0 0xFFFFFFFF

Process view

Physical Memory

OS implementation

details

Static data

(we don’t need to worry about this)

• code, global variables, compiler jump tables, etc.
• allocated at fork/exec
• never deallocated!

The Stack

as stack grows, pages

allocated as needed

(up to preset stack limit)

• function activation records
  • local vars, arguments, return values
• alloc= push ; dealloc= pop
• object lifetime: LIFO

The Heap

brk

• starts out empty
• brk pointer marks top of the heap void sbrk(int inc); _/ resizes heap by inc, returns old brk value */_

The Heap

hp

void *hp = sbrk( N );

brk

N

note: granularity of

N is page size

(really) naive malloc

void *malloc(size_t size)

void *p = sbrk(newsize);

if (p == -­‐ 1 )

return NULL;

else

return p;

free?

must support allocation & deallocation

User Process Disk RAM dynamic memory allocator sbrk Heap application program malloc OS kernel

basic issues:

• tracking free space
• tracking allocated blocks
• storing block metadata

API?

explicit memory management

vs. garbage collection (implicit mem management)