94 lines
2.2 KiB
C
94 lines
2.2 KiB
C
// Physical memory allocator, intended to allocate
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// memory for user processes, kernel stacks, page table pages,
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// and pipe buffers. Allocates 4096-byte pages.
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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 "memlayout.h"
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#include "mmu.h"
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#include "spinlock.h"
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void freerange(void *vstart, void *vend);
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extern char end[]; // first address after kernel loaded from ELF file
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// defined by the kernel linker script in kernel.ld
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struct run {
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struct run *next;
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};
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struct {
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struct spinlock lock;
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int use_lock;
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struct run *freelist;
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} kmem;
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// Initialization happens in two phases.
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// 1. main() calls kinit1() while still using entrypgdir to place just
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// the pages mapped by entrypgdir on free list.
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// 2. main() calls kinit2() with the rest of the physical pages
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// after installing a full page table that maps them on all cores.
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void kinit1(void *vstart, void *vend) {
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initlock(&kmem.lock, "kmem");
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kmem.use_lock = 0;
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freerange(vstart, vend);
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}
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void kinit2(void *vstart, void *vend) {
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freerange(vstart, vend);
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kmem.use_lock = 1;
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}
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void freerange(void *vstart, void *vend) {
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char *p;
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p = (char*)PGROUNDUP((uint)vstart);
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for (; p + PGSIZE <= (char*)vend; p += PGSIZE) {
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kfree(p);
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}
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}
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// Free the page of physical memory pointed at by v,
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// which normally should have been returned by a
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// call to kalloc(). (The exception is when
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// initializing the allocator; see kinit above.)
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void kfree(char *v) {
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struct run *r;
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if ((uint)v % PGSIZE || v < end || V2P(v) >= PHYSTOP) {
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panic("kfree");
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}
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// Fill with junk to catch dangling refs.
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memset(v, 1, PGSIZE);
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if (kmem.use_lock) {
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acquire(&kmem.lock);
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}
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r = (struct run*)v;
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r->next = kmem.freelist;
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kmem.freelist = r;
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if (kmem.use_lock) {
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release(&kmem.lock);
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}
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}
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// Allocate one 4096-byte page of physical memory.
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// Returns a pointer that the kernel can use.
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// Returns 0 if the memory cannot be allocated.
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char* kalloc(void) {
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struct run *r;
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if (kmem.use_lock) {
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acquire(&kmem.lock);
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}
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r = kmem.freelist;
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if (r) {
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kmem.freelist = r->next;
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}
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if (kmem.use_lock) {
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release(&kmem.lock);
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}
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return (char*)r;
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}
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