127 lines
2.6 KiB
C
127 lines
2.6 KiB
C
// Physical memory allocator, intended to allocate
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// memory for user processes. Allocates in 4096-byte "pages".
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// Free list is kept sorted and combines adjacent pages into
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// long runs, to make it easier to allocate big segments.
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// One reason the page size is 4k is that the x86 segment size
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// granularity is 4k.
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#include "param.h"
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#include "types.h"
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#include "defs.h"
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#include "param.h"
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#include "mmu.h"
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#include "proc.h"
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#include "spinlock.h"
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struct spinlock kalloc_lock;
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struct run {
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struct run *next;
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int len; // bytes
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};
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struct run *freelist;
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// Initialize free list of physical pages.
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// This code cheats by just considering one megabyte of
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// pages after _end. Real systems would determine the
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// amount of memory available in the system and use it all.
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void
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kinit(void)
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{
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extern int end;
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uint mem;
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char *start;
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initlock(&kalloc_lock, "kalloc");
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start = (char*) &end;
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start = (char*) (((uint)start + PAGE) & ~(PAGE-1));
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mem = 256; // assume 256 pages of RAM
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cprintf("mem = %d\n", mem * PAGE);
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kfree(start, mem * PAGE);
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}
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void
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kfree(char *cp, int len)
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{
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struct run **rr;
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struct run *p = (struct run*) cp;
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struct run *pend = (struct run*) (cp + len);
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int i;
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if(len % PAGE)
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panic("kfree");
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// Fill with junk to catch dangling refs.
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for(i = 0; i < len; i++)
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cp[i] = 1;
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acquire(&kalloc_lock);
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rr = &freelist;
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while(*rr){
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struct run *rend = (struct run*) ((char*)(*rr) + (*rr)->len);
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if(p >= *rr && p < rend)
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panic("freeing free page");
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if(pend == *rr){
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p->len = len + (*rr)->len;
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p->next = (*rr)->next;
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*rr = p;
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goto out;
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}
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if(pend < *rr){
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p->len = len;
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p->next = *rr;
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*rr = p;
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goto out;
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}
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if(p == rend){
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(*rr)->len += len;
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if((*rr)->next && (*rr)->next == pend){
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(*rr)->len += (*rr)->next->len;
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(*rr)->next = (*rr)->next->next;
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}
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goto out;
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}
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rr = &((*rr)->next);
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}
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p->len = len;
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p->next = 0;
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*rr = p;
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out:
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release(&kalloc_lock);
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}
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// Allocate n bytes of physical memory.
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// Returns a kernel-segment pointer.
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// Returns 0 if the memory cannot be allocated.
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char*
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kalloc(int n)
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{
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struct run **rr;
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if(n % PAGE)
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panic("kalloc");
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acquire(&kalloc_lock);
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rr = &freelist;
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while(*rr){
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struct run *r = *rr;
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if(r->len == n){
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*rr = r->next;
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release(&kalloc_lock);
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return (char*) r;
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}
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if(r->len > n){
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char *p = (char*)r + (r->len - n);
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r->len -= n;
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release(&kalloc_lock);
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return p;
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}
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rr = &(*rr)->next;
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}
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release(&kalloc_lock);
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cprintf("kalloc: out of memory\n");
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return 0;
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}
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