xv6/kalloc.c
2010-09-19 07:18:42 -04:00

70 lines
1.4 KiB
C

// Physical memory allocator, intended to allocate
// memory for user processes, kernel stacks, page table pages,
// and pipe buffers. Allocates 4096-byte pages.
#include "types.h"
#include "defs.h"
#include "param.h"
#include "mmu.h"
#include "spinlock.h"
struct run {
struct run *next;
};
struct {
struct spinlock lock;
struct run *freelist;
} kmem;
extern char end[]; // first address after kernel loaded from ELF file
// Initialize free list of physical pages.
void
kinit(void)
{
initlock(&kmem.lock, "kmem");
char *p = (char*)PGROUNDUP((uint)end);
for( ; p + PGSIZE - 1 < (char*) PHYSTOP; p += PGSIZE)
kfree(p);
}
//PAGEBREAK: 21
// Free the page of physical memory pointed at by v,
// which normally should have been returned by a
// call to kalloc(). (The exception is when
// initializing the allocator; see kinit above.)
void
kfree(char *v)
{
struct run *r;
if(((uint) v) % PGSIZE || v < end || (uint)v >= PHYSTOP)
panic("kfree");
// Fill with junk to catch dangling refs.
memset(v, 1, PGSIZE);
acquire(&kmem.lock);
r = (struct run *) v;
r->next = kmem.freelist;
kmem.freelist = r;
release(&kmem.lock);
}
// Allocate one 4096-byte page of physical memory.
// Returns a pointer that the kernel can use.
// Returns 0 if the memory cannot be allocated.
char*
kalloc()
{
struct run *r;
acquire(&kmem.lock);
r = kmem.freelist;
if(r)
kmem.freelist = r->next;
release(&kmem.lock);
return (char*) r;
}