111 lines
2.4 KiB
C
111 lines
2.4 KiB
C
// Physical memory allocator, intended to allocate
|
|
// memory for user processes. Allocates in 4096-byte pages.
|
|
// Free list is kept sorted and combines adjacent pages into
|
|
// long runs, to make it easier to allocate big segments.
|
|
// This combining is not useful now that xv6 uses paging.
|
|
|
|
#include "types.h"
|
|
#include "defs.h"
|
|
#include "param.h"
|
|
#include "mmu.h"
|
|
#include "spinlock.h"
|
|
|
|
struct run {
|
|
struct run *next;
|
|
int len; // bytes
|
|
};
|
|
|
|
struct {
|
|
struct spinlock lock;
|
|
struct run *freelist;
|
|
} kmem;
|
|
|
|
int nfreemem;
|
|
|
|
// Initialize free list of physical pages.
|
|
void
|
|
kinit(char *p, uint len)
|
|
{
|
|
initlock(&kmem.lock, "kmem");
|
|
nfreemem = 0;
|
|
kfree(p, len);
|
|
}
|
|
|
|
// Free the len bytes of memory pointed at by v,
|
|
// which normally should have been returned by a
|
|
// call to kalloc(len). (The exception is when
|
|
// initializing the allocator; see kinit above.)
|
|
void
|
|
kfree(char *v, int len)
|
|
{
|
|
struct run *r, *rend, **rp, *p, *pend;
|
|
|
|
if(len <= 0 || len % PGSIZE)
|
|
panic("kfree");
|
|
|
|
// Fill with junk to catch dangling refs.
|
|
memset(v, 1, len);
|
|
|
|
acquire(&kmem.lock);
|
|
nfreemem += len;
|
|
p = (struct run*)v;
|
|
pend = (struct run*)(v + len);
|
|
for(rp=&kmem.freelist; (r=*rp) != 0 && r <= pend; rp=&r->next){
|
|
rend = (struct run*)((char*)r + r->len);
|
|
if(r <= p && p < rend) {
|
|
cprintf("freeing a free page: r = 0x%x p = 0x%x rend = 0x%x\n",
|
|
r, p, rend);
|
|
panic("freeing free page");
|
|
}
|
|
if(rend == p){ // r before p: expand r to include p
|
|
r->len += len;
|
|
if(r->next && r->next == pend){ // r now next to r->next?
|
|
r->len += r->next->len;
|
|
r->next = r->next->next;
|
|
}
|
|
goto out;
|
|
}
|
|
if(pend == r){ // p before r: expand p to include, replace r
|
|
p->len = len + r->len;
|
|
p->next = r->next;
|
|
*rp = p;
|
|
goto out;
|
|
}
|
|
}
|
|
// Insert p before r in list.
|
|
p->len = len;
|
|
p->next = r;
|
|
*rp = p;
|
|
|
|
out:
|
|
release(&kmem.lock);
|
|
}
|
|
|
|
// Allocate n bytes of physical memory.
|
|
// Returns a kernel-segment pointer.
|
|
// Returns 0 if the memory cannot be allocated.
|
|
char*
|
|
kalloc(int n)
|
|
{
|
|
char *p;
|
|
struct run *r, **rp;
|
|
|
|
if(n % PGSIZE || n <= 0)
|
|
panic("kalloc");
|
|
|
|
acquire(&kmem.lock);
|
|
for(rp=&kmem.freelist; (r=*rp) != 0; rp=&r->next){
|
|
if(r->len >= n){
|
|
r->len -= n;
|
|
p = (char*)r + r->len;
|
|
if(r->len == 0)
|
|
*rp = r->next;
|
|
nfreemem -= n;
|
|
release(&kmem.lock);
|
|
return p;
|
|
}
|
|
}
|
|
release(&kmem.lock);
|
|
return 0;
|
|
}
|
|
|