#include "threads/malloc.h"
#include <debug.h>
#include <list.h>
+#include <round.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
-#include "threads/mmu.h"
#include "threads/palloc.h"
#include "threads/synch.h"
+#include "threads/vaddr.h"
/* A simple implementation of malloc().
blocks, we remove all of the arena's blocks from the free list
and give the arena back to the page allocator.
- Major limitation: the largest block that can be allocated is
- PGSIZE / 2, or 2 kB. Use palloc_get() to allocate pages (4 kB
- blocks). You're on your own if you need more memory than
- that. */
+ We can't handle blocks bigger than 2 kB using this scheme,
+ because they're too big to fit in a single page with a
+ descriptor. We handle those by allocating contiguous pages
+ with the page allocator and sticking the allocation size at
+ the beginning of the allocated block's arena header. */
/* Descriptor. */
struct desc
struct arena
{
unsigned magic; /* Always set to ARENA_MAGIC. */
- struct desc *desc; /* Owning descriptor. */
- size_t free_cnt; /* Number of free blocks. */
+ struct desc *desc; /* Owning descriptor, null for big block. */
+ size_t free_cnt; /* Free blocks; pages in big block. */
};
/* Free block. */
struct block
{
- list_elem free_elem; /* Free list element. */
+ struct list_elem free_elem; /* Free list element. */
};
/* Our set of descriptors. */
{
size_t block_size;
- for (block_size = 16; block_size < PGSIZE; block_size *= 2)
+ for (block_size = 16; block_size < PGSIZE / 2; block_size *= 2)
{
struct desc *d = &descs[desc_cnt++];
ASSERT (desc_cnt <= sizeof descs / sizeof *descs);
d->block_size = block_size;
d->blocks_per_arena = (PGSIZE - sizeof (struct arena)) / block_size;
list_init (&d->free_list);
- lock_init (&d->lock, "malloc");
+ lock_init (&d->lock);
}
}
break;
if (d == descs + desc_cnt)
{
- printf ("malloc: %zu byte allocation too big\n", size);
- return NULL;
+ /* SIZE is too big for any descriptor.
+ Allocate enough pages to hold SIZE plus an arena. */
+ size_t page_cnt = DIV_ROUND_UP (size + sizeof *a, PGSIZE);
+ a = palloc_get_multiple (0, page_cnt);
+ if (a == NULL)
+ return NULL;
+
+ /* Initialize the arena to indicate a big block of PAGE_CNT
+ pages, and return it. */
+ a->magic = ARENA_MAGIC;
+ a->desc = NULL;
+ a->free_cnt = page_cnt;
+ return a + 1;
}
lock_acquire (&d->lock);
size_t i;
/* Allocate a page. */
- a = palloc_get (0);
+ a = palloc_get_page (0);
if (a == NULL)
{
lock_release (&d->lock);
void *p;
size_t size;
- /* Calculate block size. */
+ /* Calculate block size and make sure it fits in size_t. */
size = a * b;
if (size < a || size < b)
return NULL;
return p;
}
+/* Returns the number of bytes allocated for BLOCK. */
+static size_t
+block_size (void *block)
+{
+ struct block *b = block;
+ struct arena *a = block_to_arena (b);
+ struct desc *d = a->desc;
+
+ return d != NULL ? d->block_size : PGSIZE * a->free_cnt - pg_ofs (block);
+}
+
+/* Attempts to resize OLD_BLOCK to NEW_SIZE bytes, possibly
+ moving it in the process.
+ If successful, returns the new block; on failure, returns a
+ null pointer.
+ A call with null OLD_BLOCK is equivalent to malloc(NEW_SIZE).
+ A call with zero NEW_SIZE is equivalent to free(OLD_BLOCK). */
+void *
+realloc (void *old_block, size_t new_size)
+{
+ if (new_size == 0)
+ {
+ free (old_block);
+ return NULL;
+ }
+ else
+ {
+ void *new_block = malloc (new_size);
+ if (old_block != NULL && new_block != NULL)
+ {
+ size_t old_size = block_size (old_block);
+ size_t min_size = new_size < old_size ? new_size : old_size;
+ memcpy (new_block, old_block, min_size);
+ free (old_block);
+ }
+ return new_block;
+ }
+}
+
/* Frees block P, which must have been previously allocated with
- malloc() or calloc(). */
+ malloc(), calloc(), or realloc(). */
void
free (void *p)
{
- struct block *b;
- struct arena *a;
- struct desc *d;
-
- if (p == NULL)
- return;
-
- b = p;
- a = block_to_arena (b);
- d = a->desc;
+ if (p != NULL)
+ {
+ struct block *b = p;
+ struct arena *a = block_to_arena (b);
+ struct desc *d = a->desc;
+
+ if (d != NULL)
+ {
+ /* It's a normal block. We handle it here. */
#ifndef NDEBUG
- memset (b, 0xcd, d->block_size);
+ /* Clear the block to help detect use-after-free bugs. */
+ memset (b, 0xcc, d->block_size);
#endif
- lock_acquire (&d->lock);
+ lock_acquire (&d->lock);
+ /* Add block to free list. */
+ list_push_front (&d->free_list, &b->free_elem);
- /* Add block to free list. */
- list_push_front (&d->free_list, &b->free_elem);
+ /* If the arena is now entirely unused, free it. */
+ if (++a->free_cnt >= d->blocks_per_arena)
+ {
+ size_t i;
- /* If the arena is now entirely unused, free it. */
- if (++a->free_cnt >= d->blocks_per_arena)
- {
- size_t i;
+ ASSERT (a->free_cnt == d->blocks_per_arena);
+ for (i = 0; i < d->blocks_per_arena; i++)
+ {
+ struct block *b = arena_to_block (a, i);
+ list_remove (&b->free_elem);
+ }
+ palloc_free_page (a);
+ }
- ASSERT (a->free_cnt == d->blocks_per_arena);
- for (i = 0; i < d->blocks_per_arena; i++)
+ lock_release (&d->lock);
+ }
+ else
{
- struct block *b = arena_to_block (a, i);
- list_remove (&b->free_elem);
+ /* It's a big block. Free its pages. */
+ palloc_free_multiple (a, a->free_cnt);
+ return;
}
- palloc_free (a);
}
-
- lock_release (&d->lock);
}
\f
/* Returns the arena that block B is inside. */
block_to_arena (struct block *b)
{
struct arena *a = pg_round_down (b);
+
+ /* Check that the arena is valid. */
ASSERT (a != NULL);
ASSERT (a->magic == ARENA_MAGIC);
+
+ /* Check that the block is properly aligned for the arena. */
+ ASSERT (a->desc == NULL
+ || (pg_ofs (b) - sizeof *a) % a->desc->block_size == 0);
+ ASSERT (a->desc != NULL || pg_ofs (b) == sizeof *a);
+
return a;
}
projects / pintos-anon / blobdiff