1 #include "threads/palloc.h"
10 #include "threads/loader.h"
11 #include "threads/synch.h"
12 #include "threads/vaddr.h"
14 /* Page allocator. Hands out memory in page-size (or
15 page-multiple) chunks. See malloc.h for an allocator that
16 hands out smaller chunks.
18 System memory is divided into two "pools" called the kernel
19 and user pools. The user pool is for user (virtual) memory
20 pages, the kernel pool for everything else. The idea here is
21 that the kernel needs to have memory for its own operations
22 even if user processes are swapping like mad.
24 By default, half of system RAM is given to the kernel pool and
25 half to the user pool. That should be huge overkill for the
26 kernel pool, but that's just fine for demonstration purposes. */
31 struct lock lock; /* Mutual exclusion. */
32 struct bitmap *used_map; /* Bitmap of free pages. */
33 uint8_t *base; /* Base of pool. */
36 /* Two pools: one for kernel data, one for user pages. */
37 struct pool kernel_pool, user_pool;
39 /* Maximum number of pages to put in user pool. */
40 size_t user_page_limit = SIZE_MAX;
42 static void init_pool (struct pool *, void *base, size_t page_cnt,
44 static bool page_from_pool (const struct pool *, void *page);
45 static void page_set_cache(void* page, bool enable_cache);
47 /* Initializes the page allocator. */
51 /* Free memory starts at 1 MB and runs to the end of RAM. */
52 uint8_t *free_start = ptov (1024 * 1024);
53 uint8_t *free_end = ptov (ram_pages * PGSIZE);
54 size_t free_pages = (free_end - free_start) / PGSIZE;
55 size_t user_pages = free_pages / 2;
57 if (user_pages > user_page_limit)
58 user_pages = user_page_limit;
59 kernel_pages = free_pages - user_pages;
61 /* Give half of memory to kernel, half to user. */
62 init_pool (&kernel_pool, free_start, kernel_pages, "kernel pool");
63 init_pool (&user_pool, free_start + kernel_pages * PGSIZE,
64 user_pages, "user pool");
67 /* Obtains and returns a group of PAGE_CNT contiguous free pages.
68 If PAL_USER is set, the pages are obtained from the user pool,
69 otherwise from the kernel pool. If PAL_ZERO is set in FLAGS,
70 then the pages are filled with zeros. If too few pages are
71 available, returns a null pointer, unless PAL_ASSERT is set in
72 FLAGS, in which case the kernel panics. */
74 palloc_get_multiple (enum palloc_flags flags, size_t page_cnt)
76 struct pool *pool = flags & PAL_USER ? &user_pool : &kernel_pool;
83 lock_acquire (&pool->lock);
84 page_idx = bitmap_scan_and_flip (pool->used_map, 0, page_cnt, false);
85 lock_release (&pool->lock);
87 if (page_idx != BITMAP_ERROR)
88 pages = pool->base + PGSIZE * page_idx;
95 memset (pages, 0, PGSIZE * page_cnt);
99 if (flags & PAL_ASSERT)
100 PANIC ("palloc_get: out of pages");
106 /* Obtains a single free page and returns its kernel virtual
108 If PAL_USER is set, the page is obtained from the user pool,
109 otherwise from the kernel pool. If PAL_ZERO is set in FLAGS,
110 then the page is filled with zeros. If no pages are
111 available, returns a null pointer, unless PAL_ASSERT is set in
112 FLAGS, in which case the kernel panics. */
114 palloc_get_page (enum palloc_flags flags)
116 return palloc_get_multiple (flags, 1);
119 /* Frees the PAGE_CNT pages starting at PAGES. */
121 palloc_free_multiple (void *pages, size_t page_cnt)
126 ASSERT (pg_ofs (pages) == 0);
127 if (pages == NULL || page_cnt == 0)
130 if (page_from_pool (&kernel_pool, pages))
132 else if (page_from_pool (&user_pool, pages))
137 page_idx = pg_no (pages) - pg_no (pool->base);
140 memset (pages, 0xcc, PGSIZE * page_cnt);
143 ASSERT (bitmap_all (pool->used_map, page_idx, page_cnt));
144 bitmap_set_multiple (pool->used_map, page_idx, page_cnt, false);
147 /* Frees the page at PAGE. */
149 palloc_free_page (void *page)
151 palloc_free_multiple (page, 1);
154 /* Initializes pool P as starting at START and ending at END,
155 naming it NAME for debugging purposes. */
157 init_pool (struct pool *p, void *base, size_t page_cnt, const char *name)
159 /* We'll put the pool's used_map at its base.
160 Calculate the space needed for the bitmap
161 and subtract it from the pool's size. */
162 size_t bm_pages = DIV_ROUND_UP (bitmap_buf_size (page_cnt), PGSIZE);
163 if (bm_pages > page_cnt)
164 PANIC ("Not enough memory in %s for bitmap.", name);
165 page_cnt -= bm_pages;
167 printf ("%zu pages available in %s.\n", page_cnt, name);
169 /* Initialize the pool. */
170 lock_init (&p->lock);
171 p->used_map = bitmap_create_in_buf (page_cnt, base, bm_pages * PGSIZE);
172 p->base = base + bm_pages * PGSIZE;
175 /* Returns true if PAGE was allocated from POOL,
178 page_from_pool (const struct pool *pool, void *page)
180 size_t page_no = pg_no (page);
181 size_t start_page = pg_no (pool->base);
182 size_t end_page = start_page + bitmap_size (pool->used_map);
184 return page_no >= start_page && page_no < end_page;