2 * SLOB Allocator: Simple List Of Blocks
4 * Matt Mackall <mpm@selenic.com> 12/30/03
8 * The core of SLOB is a traditional K&R style heap allocator, with
9 * support for returning aligned objects. The granularity of this
10 * allocator is 8 bytes on x86, though it's perhaps possible to reduce
11 * this to 4 if it's deemed worth the effort. The slob heap is a
12 * singly-linked list of pages from __get_free_page, grown on demand
13 * and allocation from the heap is currently first-fit.
15 * Above this is an implementation of kmalloc/kfree. Blocks returned
16 * from kmalloc are 8-byte aligned and prepended with a 8-byte header.
17 * If kmalloc is asked for objects of PAGE_SIZE or larger, it calls
18 * __get_free_pages directly so that it can return page-aligned blocks
19 * and keeps a linked list of such pages and their orders. These
20 * objects are detected in kfree() by their page alignment.
22 * SLAB is emulated on top of SLOB by simply calling constructors and
23 * destructors for every SLAB allocation. Objects are returned with
24 * the 8-byte alignment unless the SLAB_MUST_HWCACHE_ALIGN flag is
25 * set, in which case the low-level allocator will fragment blocks to
26 * create the proper alignment. Again, objects of page-size or greater
27 * are allocated by calling __get_free_pages. As SLAB objects know
28 * their size, no separate size bookkeeping is necessary and there is
29 * essentially no allocation space overhead.
32 #include <linux/slab.h>
34 #include <linux/cache.h>
35 #include <linux/init.h>
36 #include <linux/module.h>
37 #include <linux/timer.h>
41 struct slob_block *next;
43 typedef struct slob_block slob_t;
45 #define SLOB_UNIT sizeof(slob_t)
46 #define SLOB_UNITS(size) (((size) + SLOB_UNIT - 1)/SLOB_UNIT)
47 #define SLOB_ALIGN L1_CACHE_BYTES
52 struct bigblock *next;
54 typedef struct bigblock bigblock_t;
56 static slob_t arena = { .next = &arena, .units = 1 };
57 static slob_t *slobfree = &arena;
58 static bigblock_t *bigblocks;
59 static DEFINE_SPINLOCK(slob_lock);
60 static DEFINE_SPINLOCK(block_lock);
62 static void slob_free(void *b, int size);
64 static void *slob_alloc(size_t size, gfp_t gfp, int align)
66 slob_t *prev, *cur, *aligned = 0;
67 int delta = 0, units = SLOB_UNITS(size);
70 spin_lock_irqsave(&slob_lock, flags);
72 for (cur = prev->next; ; prev = cur, cur = cur->next) {
74 aligned = (slob_t *)ALIGN((unsigned long)cur, align);
75 delta = aligned - cur;
77 if (cur->units >= units + delta) { /* room enough? */
78 if (delta) { /* need to fragment head to align? */
79 aligned->units = cur->units - delta;
80 aligned->next = cur->next;
87 if (cur->units == units) /* exact fit? */
88 prev->next = cur->next; /* unlink */
90 prev->next = cur + units;
91 prev->next->units = cur->units - units;
92 prev->next->next = cur->next;
97 spin_unlock_irqrestore(&slob_lock, flags);
100 if (cur == slobfree) {
101 spin_unlock_irqrestore(&slob_lock, flags);
103 if (size == PAGE_SIZE) /* trying to shrink arena? */
106 cur = (slob_t *)__get_free_page(gfp);
110 slob_free(cur, PAGE_SIZE);
111 spin_lock_irqsave(&slob_lock, flags);
117 static void slob_free(void *block, int size)
119 slob_t *cur, *b = (slob_t *)block;
126 b->units = SLOB_UNITS(size);
128 /* Find reinsertion point */
129 spin_lock_irqsave(&slob_lock, flags);
130 for (cur = slobfree; !(b > cur && b < cur->next); cur = cur->next)
131 if (cur >= cur->next && (b > cur || b < cur->next))
134 if (b + b->units == cur->next) {
135 b->units += cur->next->units;
136 b->next = cur->next->next;
140 if (cur + cur->units == b) {
141 cur->units += b->units;
148 spin_unlock_irqrestore(&slob_lock, flags);
151 static int FASTCALL(find_order(int size));
152 static int fastcall find_order(int size)
155 for ( ; size > 4096 ; size >>=1)
160 void *kmalloc(size_t size, gfp_t gfp)
166 if (size < PAGE_SIZE - SLOB_UNIT) {
167 m = slob_alloc(size + SLOB_UNIT, gfp, 0);
168 return m ? (void *)(m + 1) : 0;
171 bb = slob_alloc(sizeof(bigblock_t), gfp, 0);
175 bb->order = find_order(size);
176 bb->pages = (void *)__get_free_pages(gfp, bb->order);
179 spin_lock_irqsave(&block_lock, flags);
180 bb->next = bigblocks;
182 spin_unlock_irqrestore(&block_lock, flags);
186 slob_free(bb, sizeof(bigblock_t));
190 EXPORT_SYMBOL(kmalloc);
192 void kfree(const void *block)
194 bigblock_t *bb, **last = &bigblocks;
200 if (!((unsigned long)block & (PAGE_SIZE-1))) {
201 /* might be on the big block list */
202 spin_lock_irqsave(&block_lock, flags);
203 for (bb = bigblocks; bb; last = &bb->next, bb = bb->next) {
204 if (bb->pages == block) {
206 spin_unlock_irqrestore(&block_lock, flags);
207 free_pages((unsigned long)block, bb->order);
208 slob_free(bb, sizeof(bigblock_t));
212 spin_unlock_irqrestore(&block_lock, flags);
215 slob_free((slob_t *)block - 1, 0);
219 EXPORT_SYMBOL(kfree);
221 unsigned int ksize(const void *block)
229 if (!((unsigned long)block & (PAGE_SIZE-1))) {
230 spin_lock_irqsave(&block_lock, flags);
231 for (bb = bigblocks; bb; bb = bb->next)
232 if (bb->pages == block) {
233 spin_unlock_irqrestore(&slob_lock, flags);
234 return PAGE_SIZE << bb->order;
236 spin_unlock_irqrestore(&block_lock, flags);
239 return ((slob_t *)block - 1)->units * SLOB_UNIT;
243 unsigned int size, align;
245 void (*ctor)(void *, struct kmem_cache *, unsigned long);
246 void (*dtor)(void *, struct kmem_cache *, unsigned long);
249 struct kmem_cache *kmem_cache_create(const char *name, size_t size,
250 size_t align, unsigned long flags,
251 void (*ctor)(void*, struct kmem_cache *, unsigned long),
252 void (*dtor)(void*, struct kmem_cache *, unsigned long))
254 struct kmem_cache *c;
256 c = slob_alloc(sizeof(struct kmem_cache), flags, 0);
263 /* ignore alignment unless it's forced */
264 c->align = (flags & SLAB_MUST_HWCACHE_ALIGN) ? SLOB_ALIGN : 0;
265 if (c->align < align)
271 EXPORT_SYMBOL(kmem_cache_create);
273 int kmem_cache_destroy(struct kmem_cache *c)
275 slob_free(c, sizeof(struct kmem_cache));
278 EXPORT_SYMBOL(kmem_cache_destroy);
280 void *kmem_cache_alloc(struct kmem_cache *c, gfp_t flags)
284 if (c->size < PAGE_SIZE)
285 b = slob_alloc(c->size, flags, c->align);
287 b = (void *)__get_free_pages(flags, find_order(c->size));
290 c->ctor(b, c, SLAB_CTOR_CONSTRUCTOR);
294 EXPORT_SYMBOL(kmem_cache_alloc);
296 void *kmem_cache_zalloc(struct kmem_cache *c, gfp_t flags)
298 void *ret = kmem_cache_alloc(c, flags);
300 memset(ret, 0, c->size);
304 EXPORT_SYMBOL(kmem_cache_zalloc);
306 void kmem_cache_free(struct kmem_cache *c, void *b)
311 if (c->size < PAGE_SIZE)
312 slob_free(b, c->size);
314 free_pages((unsigned long)b, find_order(c->size));
316 EXPORT_SYMBOL(kmem_cache_free);
318 unsigned int kmem_cache_size(struct kmem_cache *c)
322 EXPORT_SYMBOL(kmem_cache_size);
324 const char *kmem_cache_name(struct kmem_cache *c)
328 EXPORT_SYMBOL(kmem_cache_name);
330 static struct timer_list slob_timer = TIMER_INITIALIZER(
331 (void (*)(unsigned long))kmem_cache_init, 0, 0);
333 void kmem_cache_init(void)
335 void *p = slob_alloc(PAGE_SIZE, 0, PAGE_SIZE-1);
338 free_page((unsigned long)p);
340 mod_timer(&slob_timer, jiffies + HZ);