xv6-cs450/kalloc.c
Robert Morris 8d774afb2d no more pminit, or ELF header at 0x10000
kinit() knows about end and PHYSTOP
map all of kernel read/write (rather than r/o instructions)
thanks, austin
2010-08-31 15:39:25 -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;
// Initialize free list of physical pages.
void
kinit(void)
{
extern char end[];
initlock(&kmem.lock, "kmem");
char *p1 = (char*)PGROUNDUP((uint)end);
char *p2 = PGROUNDDOWN(PHYSTOP);
for( ; p1 < p2; p1 += 4096)
kfree(p1);
}
// 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 || (uint)v < 1024*1024 || (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;
}