provided code

src/threads/malloc.c

@@ -0,0 +1,294 @@
+#include "threads/malloc.h"
+#include <debug.h>
+#include <list.h>
+#include <round.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+#include "threads/palloc.h"
+#include "threads/synch.h"
+#include "threads/vaddr.h"
+
+/* A simple implementation of malloc().
+
+   The size of each request, in bytes, is rounded up to a power
+   of 2 and assigned to the "descriptor" that manages blocks of
+   that size.  The descriptor keeps a list of free blocks.  If
+   the free list is nonempty, one of its blocks is used to
+   satisfy the request.
+
+   Otherwise, a new page of memory, called an "arena", is
+   obtained from the page allocator (if none is available,
+   malloc() returns a null pointer).  The new arena is divided
+   into blocks, all of which are added to the descriptor's free
+   list.  Then we return one of the new blocks.
+
+   When we free a block, we add it to its descriptor's free list.
+   But if the arena that the block was in now has no in-use
+   blocks, we remove all of the arena's blocks from the free list
+   and give the arena back to the page allocator.
+
+   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
+  {
+    size_t block_size;          /* Size of each element in bytes. */
+    size_t blocks_per_arena;    /* Number of blocks in an arena. */
+    struct list free_list;      /* List of free blocks. */
+    struct lock lock;           /* Lock. */
+  };
+
+/* Magic number for detecting arena corruption. */
+#define ARENA_MAGIC 0x9a548eed
+
+/* Arena. */
+struct arena 
+  {
+    unsigned magic;             /* Always set to ARENA_MAGIC. */
+    struct desc *desc;          /* Owning descriptor, null for big block. */
+    size_t free_cnt;            /* Free blocks; pages in big block. */
+  };
+
+/* Free block. */
+struct block 
+  {
+    struct list_elem free_elem; /* Free list element. */
+  };
+
+/* Our set of descriptors. */
+static struct desc descs[10];   /* Descriptors. */
+static size_t desc_cnt;         /* Number of descriptors. */
+
+static struct arena *block_to_arena (struct block *);
+static struct block *arena_to_block (struct arena *, size_t idx);
+
+/* Initializes the malloc() descriptors. */
+void
+malloc_init (void) 
+{
+  size_t block_size;
+
+  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);
+    }
+}
+
+/* Obtains and returns a new block of at least SIZE bytes.
+   Returns a null pointer if memory is not available. */
+void *
+malloc (size_t size) 
+{
+  struct desc *d;
+  struct block *b;
+  struct arena *a;
+
+  /* A null pointer satisfies a request for 0 bytes. */
+  if (size == 0)
+    return NULL;
+
+  /* Find the smallest descriptor that satisfies a SIZE-byte
+     request. */
+  for (d = descs; d < descs + desc_cnt; d++)
+    if (d->block_size >= size)
+      break;
+  if (d == descs + desc_cnt) 
+    {
+      /* 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);
+
+  /* If the free list is empty, create a new arena. */
+  if (list_empty (&d->free_list))
+    {
+      size_t i;
+
+      /* Allocate a page. */
+      a = palloc_get_page (0);
+      if (a == NULL) 
+        {
+          lock_release (&d->lock);
+          return NULL; 
+        }
+
+      /* Initialize arena and add its blocks to the free list. */
+      a->magic = ARENA_MAGIC;
+      a->desc = d;
+      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_push_back (&d->free_list, &b->free_elem);
+        }
+    }
+
+  /* Get a block from free list and return it. */
+  b = list_entry (list_pop_front (&d->free_list), struct block, free_elem);
+  a = block_to_arena (b);
+  a->free_cnt--;
+  lock_release (&d->lock);
+  return b;
+}
+
+/* Allocates and return A times B bytes initialized to zeroes.
+   Returns a null pointer if memory is not available. */
+void *
+calloc (size_t a, size_t b) 
+{
+  void *p;
+  size_t size;
+
+  /* Calculate block size and make sure it fits in size_t. */
+  size = a * b;
+  if (size < a || size < b)
+    return NULL;
+
+  /* Allocate and zero memory. */
+  p = malloc (size);
+  if (p != NULL)
+    memset (p, 0, size);
+
+  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(), calloc(), or realloc(). */
+void
+free (void *p) 
+{
+  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
+          /* Clear the block to help detect use-after-free bugs. */
+          memset (b, 0xcc, d->block_size);
+#endif
+  
+          lock_acquire (&d->lock);
+
+          /* 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;
+
+              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);
+            }
+
+          lock_release (&d->lock);
+        }
+      else
+        {
+          /* It's a big block.  Free its pages. */
+          palloc_free_multiple (a, a->free_cnt);
+          return;
+        }
+    }
+}
+
+/* Returns the arena that block B is inside. */
+static struct arena *
+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;
+}
+
+/* Returns the (IDX - 1)'th block within arena A. */
+static struct block *
+arena_to_block (struct arena *a, size_t idx) 
+{
+  ASSERT (a != NULL);
+  ASSERT (a->magic == ARENA_MAGIC);
+  ASSERT (idx < a->desc->blocks_per_arena);
+  return (struct block *) ((uint8_t *) a
+                           + sizeof *a
+                           + idx * a->desc->block_size);
+}