added kalloc

kalloc.c

@@ -0,0 +1,194 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "kalloc.h"
+
+/* In kalloc, a *core* is a large chunk of contiguous memory. Each core is
+ * associated with a master header, which keeps the size of the current core
+ * and the pointer to next core. Kalloc allocates small *blocks* of memory from
+ * the cores and organizes free memory blocks in a circular single-linked list.
+ *
+ * In the following diagram, "@" stands for the header of a free block (of type
+ * header_t), "#" for the header of an allocated block (of type size_t), "-"
+ * for free memory, and "+" for allocated memory.
+ *
+ * master        This region is core 1.          master           This region is core 2.
+ *      |                                             |
+ *      *@-------#++++++#++++++++++++@--------        *@----------#++++++++++++#+++++++@------------
+ *       |                           |                 |                               |
+ *       p=p->ptr->ptr->ptr->ptr     p->ptr            p->ptr->ptr                     p->ptr->ptr->ptr
+ */
+
+#define MIN_CORE_SIZE 0x80000
+
+typedef struct header_t {
+	size_t size;
+	struct header_t *ptr;
+} header_t;
+
+typedef struct {
+	header_t base, *loop_head, *core_head; /* base is a zero-sized block always kept in the loop */
+} kmem_t;
+
+static void panic(const char *s)
+{
+	fprintf(stderr, "%s\n", s);
+	abort();
+}
+
+void *km_init(void)
+{
+	return calloc(1, sizeof(kmem_t));
+}
+
+void km_destroy(void *_km)
+{
+	kmem_t *km = (kmem_t*)_km;
+	header_t *p, *q;
+	if (km == NULL) return;
+	for (p = km->core_head; p != NULL;) {
+		q = p->ptr;
+		free(p);
+		p = q;
+	}
+	free(km);
+}
+
+static header_t *morecore(kmem_t *km, size_t nu)
+{
+	header_t *q;
+	size_t bytes, *p;
+	nu = (nu + 1 + (MIN_CORE_SIZE - 1)) / MIN_CORE_SIZE * MIN_CORE_SIZE; /* the first +1 for core header */
+	bytes = nu * sizeof(header_t);
+	q = (header_t*)malloc(bytes);
+	if (!q) panic("[morecore] insufficient memory");
+	q->ptr = km->core_head, q->size = nu, km->core_head = q;
+	p = (size_t*)(q + 1);
+	*p = nu - 1; /* the size of the free block; -1 because the first unit is used for the core header */
+	kfree(km, p + 1); /* initialize the new "core"; NB: the core header is not looped. */
+	return km->loop_head;
+}
+
+void kfree(void *_km, void *ap) /* kfree() also adds a new core to the circular list */
+{
+	header_t *p, *q;
+	kmem_t *km = (kmem_t*)_km;
+	
+	if (!ap) return;
+	if (km == NULL) {
+		free(ap);
+		return;
+	}
+	p = (header_t*)((size_t*)ap - 1);
+	p->size = *((size_t*)ap - 1);
+	/* Find the pointer that points to the block to be freed. The following loop can stop on two conditions:
+	 *
+	 * a) "p>q && p<q->ptr": @------#++++++++#+++++++@-------    @---------------#+++++++@-------
+	 *    (can also be in    |      |                |        -> |                       |
+	 *     two cores)        q      p           q->ptr           q                  q->ptr
+	 *
+	 *                       @--------    #+++++++++@--------    @--------    @------------------
+	 *                       |            |         |         -> |            |
+	 *                       q            p    q->ptr            q       q->ptr
+	 *
+	 * b) "q>=q->ptr && (p>q || p<q->ptr)":  @-------#+++++   @--------#+++++++     @-------#+++++   @----------------
+	 *                                       |                |        |         -> |                |
+	 *                                  q->ptr                q        p       q->ptr                q
+	 *
+	 *                                       #+++++++@-----   #++++++++@-------     @-------------   #++++++++@-------
+	 *                                       |       |                 |         -> |                         |
+	 *                                       p  q->ptr                 q       q->ptr                         q
+	 */
+	for (q = km->loop_head; !(p > q && p < q->ptr); q = q->ptr)
+		if (q >= q->ptr && (p > q || p < q->ptr)) break;
+	if (p + p->size == q->ptr) { /* two adjacent blocks, merge p and q->ptr (the 2nd and 4th cases) */
+		p->size += q->ptr->size;
+		p->ptr = q->ptr->ptr;
+	} else if (p + p->size > q->ptr && q->ptr >= p) {
+		panic("[kfree] The end of the allocated block enters a free block.");
+	} else p->ptr = q->ptr; /* backup q->ptr */
+
+	if (q + q->size == p) { /* two adjacent blocks, merge q and p (the other two cases) */
+		q->size += p->size;
+		q->ptr = p->ptr;
+		km->loop_head = q;
+	} else if (q + q->size > p && p >= q) {
+		panic("[kfree] The end of a free block enters the allocated block.");
+	} else km->loop_head = p, q->ptr = p; /* in two cores, cannot be merged; create a new block in the list */
+}
+
+void *kmalloc(void *_km, size_t n_bytes)
+{
+	kmem_t *km = (kmem_t*)_km;
+	size_t n_units;
+	header_t *p, *q;
+
+	if (n_bytes == 0) return 0;
+	if (km == NULL) return malloc(n_bytes);
+	n_units = (n_bytes + sizeof(size_t) + sizeof(header_t) - 1) / sizeof(header_t) + 1;
+
+	if (!(q = km->loop_head)) /* the first time when kmalloc() is called, intialize it */
+		q = km->loop_head = km->base.ptr = &km->base;
+	for (p = q->ptr;; q = p, p = p->ptr) { /* search for a suitable block */
+		if (p->size >= n_units) { /* p->size if the size of current block. This line means the current block is large enough. */
+			if (p->size == n_units) q->ptr = p->ptr; /* no need to split the block */
+			else { /* split the block. NB: memory is allocated at the end of the block! */
+				p->size -= n_units; /* reduce the size of the free block */
+				p += p->size; /* p points to the allocated block */
+				*(size_t*)p = n_units; /* set the size */
+			}
+			km->loop_head = q; /* set the end of chain */
+			return (size_t*)p + 1;
+		}
+		if (p == km->loop_head) { /* then ask for more "cores" */
+			if ((p = morecore(km, n_units)) == 0) return 0;
+		}
+	}
+}
+
+void *kcalloc(void *_km, size_t count, size_t size)
+{
+	kmem_t *km = (kmem_t*)_km;
+	void *p;
+	if (size == 0 || count == 0) return 0;
+	if (km == NULL) return calloc(count, size);
+	p = kmalloc(km, count * size);
+	memset(p, 0, count * size);
+	return p;
+}
+
+void *krealloc(void *_km, void *ap, size_t n_bytes) // TODO: this can be made more efficient in principle
+{
+	kmem_t *km = (kmem_t*)_km;
+	size_t n_units, *p, *q;
+
+	if (n_bytes == 0) {
+		kfree(km, ap); return 0;
+	}
+	if (km == NULL) return realloc(ap, n_bytes);
+	if (ap == NULL) return kmalloc(km, n_bytes);
+	n_units = (n_bytes + sizeof(size_t) + sizeof(header_t) - 1) / sizeof(header_t);
+	p = (size_t*)ap - 1;
+	if (*p >= n_units) return ap; /* TODO: this prevents shrinking */
+	q = (size_t*)kmalloc(km, n_bytes);
+	memcpy(q, ap, (*p - 1) * sizeof(header_t));
+	kfree(km, ap);
+	return q;
+}
+
+void km_stat(const void *_km, km_stat_t *s)
+{
+	kmem_t *km = (kmem_t*)_km;
+	header_t *p;
+	memset(s, 0, sizeof(km_stat_t));
+	if (km == NULL || km->loop_head == NULL) return;
+	for (p = km->loop_head;; p = p->ptr) {
+		s->available += p->size * sizeof(header_t);
+		if (p->size != 0) ++s->n_blocks; /* &kmem_t::base is always one of the cores. It is zero-sized. */
+		if (p->ptr > p && p + p->size > p->ptr)
+			panic("[km_stat] The end of a free block enters another free block.");
+		if (p->ptr == km->loop_head) break;
+	}
+	for (p = km->core_head; p != NULL; p = p->ptr)
+		++s->n_cores, s->capacity += p->size * sizeof(header_t);
+}

kalloc.h

@@ -0,0 +1,27 @@
+#ifndef _KALLOC_H_
+#define _KALLOC_H_
+
+#include <stddef.h> /* for size_t */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct {
+	size_t capacity, available, n_blocks, n_cores;
+} km_stat_t;
+
+void *kmalloc(void *km, size_t size);
+void *krealloc(void *km, void *ptr, size_t size);
+void *kcalloc(void *km, size_t count, size_t size);
+void kfree(void *km, void *ptr);
+
+void *km_init(void);
+void km_destroy(void *km);
+void km_stat(const void *_km, km_stat_t *s);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif