root/kalloc.c
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DEFINITIONS
This source file includes following definitions.
- kinit1
- kinit2
- freerange
- kfree
- kalloc
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
12 void freerange(void *vstart, void *vend);
13 extern char end[]; // first address after kernel loaded from ELF file
14
15 struct run {
16 struct run *next;
17 };
18
19 struct {
20 struct spinlock lock;
21 int use_lock;
22 struct run *freelist;
23 } kmem;
24
25 // Initialization happens in two phases.
26 // 1. main() calls kinit1() while still using entrypgdir to place just
27 // the pages mapped by entrypgdir on free list.
28 // 2. main() calls kinit2() with the rest of the physical pages
29 // after installing a full page table that maps them on all cores.
30 void
31 kinit1(void *vstart, void *vend)
32 {
33 initlock(&kmem.lock, "kmem");
34 kmem.use_lock = 0;
35 freerange(vstart, vend);
36 }
37
38 void
39 kinit2(void *vstart, void *vend)
40 {
41 freerange(vstart, vend);
42 kmem.use_lock = 1;
43 }
44
45 void
46 freerange(void *vstart, void *vend)
47 {
48 char *p;
49 p = (char*)PGROUNDUP((uint)vstart);
50 for(; p + PGSIZE <= (char*)vend; p += PGSIZE)
51 kfree(p);
52 }
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.)
59 void
60 kfree(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.
82 char*
83 kalloc(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