1// Physical memory allocator, intended to allocate
2// memory for user processes, kernel stacks, page table pages,
3// and pipe buffers. Allocates 4096-byte pages.
4
5#include "types.h"
6#include "defs.h"
7#include "param.h"
8#include "memlayout.h"
9#include "mmu.h"
10#include "spinlock.h"
11
12void freerange(void *vstart, void *vend);
13extern char end[]; // first address after kernel loaded from ELF file
14 // defined by the kernel linker script in kernel.ld
15
16struct run {
17 struct run *next;
18};
19
20struct {
21 struct spinlock lock;
22 int use_lock;
23 struct run *freelist;
24} kmem;
25
26// Initialization happens in two phases.
27// 1. main() calls kinit1() while still using entrypgdir to place just
28// the pages mapped by entrypgdir on free list.
29// 2. main() calls kinit2() with the rest of the physical pages
30// after installing a full page table that maps them on all cores.
31void
32kinit1(void *vstart, void *vend)
33{
34 initlock(&kmem.lock, "kmem");
35 kmem.use_lock = 0;
36 freerange(vstart, vend);
37}
38
39void
40kinit2(void *vstart, void *vend)
41{
42 freerange(vstart, vend);
43 kmem.use_lock = 1;
44}
45
46void
47freerange(void *vstart, void *vend)
48{
49 char *p;
50 p = (char*)PGROUNDUP((uint)vstart);
51 for(; p + PGSIZE <= (char*)vend; p += PGSIZE)
52 kfree(p);
53}
54//PAGEBREAK: 21
55// Free the page of physical memory pointed at by v,
56// which normally should have been returned by a
57// call to kalloc(). (The exception is when
58// initializing the allocator; see kinit above.)
59void
60kfree(char *v)
61{
62 struct run *r;
63
64 if((uint)v % PGSIZE || v < end || V2P(v) >= PHYSTOP)
65 panic("kfree");
66
67 // Fill with junk to catch dangling refs.
68 memset(v, 1, PGSIZE);
69
70 if(kmem.use_lock)
71 acquire(&kmem.lock);
72 r = (struct run*)v;
73 r->next = kmem.freelist;
74 kmem.freelist = r;
75 if(kmem.use_lock)
76 release(&kmem.lock);
77}
78
79// Allocate one 4096-byte page of physical memory.
80// Returns a pointer that the kernel can use.
81// Returns 0 if the memory cannot be allocated.
82char*
83kalloc(void)
84{
85 struct run *r;
86
87 if(kmem.use_lock)
88 acquire(&kmem.lock);
89 r = kmem.freelist;
90 if(r)
91 kmem.freelist = r->next;
92 if(kmem.use_lock)
93 release(&kmem.lock);
94 return (char*)r;
95}
96
97