slob.c revision 6ab3d5624e172c553004ecc862bfeac16d9d68b7 
1/*
2 * SLOB Allocator: Simple List Of Blocks
3 *
4 * Matt Mackall <mpm@selenic.com> 12/30/03
5 *
6 * How SLOB works:
7 *
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.
14 *
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.
21 *
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.
30 */
31
32#include <linux/slab.h>
33#include <linux/mm.h>
34#include <linux/cache.h>
35#include <linux/init.h>
36#include <linux/module.h>
37#include <linux/timer.h>
38
39struct slob_block {
40	int units;
41	struct slob_block *next;
42};
43typedef struct slob_block slob_t;
44
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
48
49struct bigblock {
50	int order;
51	void *pages;
52	struct bigblock *next;
53};
54typedef struct bigblock bigblock_t;
55
56static slob_t arena = { .next = &arena, .units = 1 };
57static slob_t *slobfree = &arena;
58static bigblock_t *bigblocks;
59static DEFINE_SPINLOCK(slob_lock);
60static DEFINE_SPINLOCK(block_lock);
61
62static void slob_free(void *b, int size);
63
64static void *slob_alloc(size_t size, gfp_t gfp, int align)
65{
66	slob_t *prev, *cur, *aligned = 0;
67	int delta = 0, units = SLOB_UNITS(size);
68	unsigned long flags;
69
70	spin_lock_irqsave(&slob_lock, flags);
71	prev = slobfree;
72	for (cur = prev->next; ; prev = cur, cur = cur->next) {
73		if (align) {
74			aligned = (slob_t *)ALIGN((unsigned long)cur, align);
75			delta = aligned - cur;
76		}
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;
81				cur->next = aligned;
82				cur->units = delta;
83				prev = cur;
84				cur = aligned;
85			}
86
87			if (cur->units == units) /* exact fit? */
88				prev->next = cur->next; /* unlink */
89			else { /* fragment */
90				prev->next = cur + units;
91				prev->next->units = cur->units - units;
92				prev->next->next = cur->next;
93				cur->units = units;
94			}
95
96			slobfree = prev;
97			spin_unlock_irqrestore(&slob_lock, flags);
98			return cur;
99		}
100		if (cur == slobfree) {
101			spin_unlock_irqrestore(&slob_lock, flags);
102
103			if (size == PAGE_SIZE) /* trying to shrink arena? */
104				return 0;
105
106			cur = (slob_t *)__get_free_page(gfp);
107			if (!cur)
108				return 0;
109
110			slob_free(cur, PAGE_SIZE);
111			spin_lock_irqsave(&slob_lock, flags);
112			cur = slobfree;
113		}
114	}
115}
116
117static void slob_free(void *block, int size)
118{
119	slob_t *cur, *b = (slob_t *)block;
120	unsigned long flags;
121
122	if (!block)
123		return;
124
125	if (size)
126		b->units = SLOB_UNITS(size);
127
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))
132			break;
133
134	if (b + b->units == cur->next) {
135		b->units += cur->next->units;
136		b->next = cur->next->next;
137	} else
138		b->next = cur->next;
139
140	if (cur + cur->units == b) {
141		cur->units += b->units;
142		cur->next = b->next;
143	} else
144		cur->next = b;
145
146	slobfree = cur;
147
148	spin_unlock_irqrestore(&slob_lock, flags);
149}
150
151static int FASTCALL(find_order(int size));
152static int fastcall find_order(int size)
153{
154	int order = 0;
155	for ( ; size > 4096 ; size >>=1)
156		order++;
157	return order;
158}
159
160void *kmalloc(size_t size, gfp_t gfp)
161{
162	slob_t *m;
163	bigblock_t *bb;
164	unsigned long flags;
165
166	if (size < PAGE_SIZE - SLOB_UNIT) {
167		m = slob_alloc(size + SLOB_UNIT, gfp, 0);
168		return m ? (void *)(m + 1) : 0;
169	}
170
171	bb = slob_alloc(sizeof(bigblock_t), gfp, 0);
172	if (!bb)
173		return 0;
174
175	bb->order = find_order(size);
176	bb->pages = (void *)__get_free_pages(gfp, bb->order);
177
178	if (bb->pages) {
179		spin_lock_irqsave(&block_lock, flags);
180		bb->next = bigblocks;
181		bigblocks = bb;
182		spin_unlock_irqrestore(&block_lock, flags);
183		return bb->pages;
184	}
185
186	slob_free(bb, sizeof(bigblock_t));
187	return 0;
188}
189
190EXPORT_SYMBOL(kmalloc);
191
192void kfree(const void *block)
193{
194	bigblock_t *bb, **last = &bigblocks;
195	unsigned long flags;
196
197	if (!block)
198		return;
199
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) {
205				*last = bb->next;
206				spin_unlock_irqrestore(&block_lock, flags);
207				free_pages((unsigned long)block, bb->order);
208				slob_free(bb, sizeof(bigblock_t));
209				return;
210			}
211		}
212		spin_unlock_irqrestore(&block_lock, flags);
213	}
214
215	slob_free((slob_t *)block - 1, 0);
216	return;
217}
218
219EXPORT_SYMBOL(kfree);
220
221unsigned int ksize(const void *block)
222{
223	bigblock_t *bb;
224	unsigned long flags;
225
226	if (!block)
227		return 0;
228
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;
235			}
236		spin_unlock_irqrestore(&block_lock, flags);
237	}
238
239	return ((slob_t *)block - 1)->units * SLOB_UNIT;
240}
241
242struct kmem_cache {
243	unsigned int size, align;
244	const char *name;
245	void (*ctor)(void *, struct kmem_cache *, unsigned long);
246	void (*dtor)(void *, struct kmem_cache *, unsigned long);
247};
248
249struct 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))
253{
254	struct kmem_cache *c;
255
256	c = slob_alloc(sizeof(struct kmem_cache), flags, 0);
257
258	if (c) {
259		c->name = name;
260		c->size = size;
261		c->ctor = ctor;
262		c->dtor = dtor;
263		/* ignore alignment unless it's forced */
264		c->align = (flags & SLAB_MUST_HWCACHE_ALIGN) ? SLOB_ALIGN : 0;
265		if (c->align < align)
266			c->align = align;
267	}
268
269	return c;
270}
271EXPORT_SYMBOL(kmem_cache_create);
272
273int kmem_cache_destroy(struct kmem_cache *c)
274{
275	slob_free(c, sizeof(struct kmem_cache));
276	return 0;
277}
278EXPORT_SYMBOL(kmem_cache_destroy);
279
280void *kmem_cache_alloc(struct kmem_cache *c, gfp_t flags)
281{
282	void *b;
283
284	if (c->size < PAGE_SIZE)
285		b = slob_alloc(c->size, flags, c->align);
286	else
287		b = (void *)__get_free_pages(flags, find_order(c->size));
288
289	if (c->ctor)
290		c->ctor(b, c, SLAB_CTOR_CONSTRUCTOR);
291
292	return b;
293}
294EXPORT_SYMBOL(kmem_cache_alloc);
295
296void *kmem_cache_zalloc(struct kmem_cache *c, gfp_t flags)
297{
298	void *ret = kmem_cache_alloc(c, flags);
299	if (ret)
300		memset(ret, 0, c->size);
301
302	return ret;
303}
304EXPORT_SYMBOL(kmem_cache_zalloc);
305
306void kmem_cache_free(struct kmem_cache *c, void *b)
307{
308	if (c->dtor)
309		c->dtor(b, c, 0);
310
311	if (c->size < PAGE_SIZE)
312		slob_free(b, c->size);
313	else
314		free_pages((unsigned long)b, find_order(c->size));
315}
316EXPORT_SYMBOL(kmem_cache_free);
317
318unsigned int kmem_cache_size(struct kmem_cache *c)
319{
320	return c->size;
321}
322EXPORT_SYMBOL(kmem_cache_size);
323
324const char *kmem_cache_name(struct kmem_cache *c)
325{
326	return c->name;
327}
328EXPORT_SYMBOL(kmem_cache_name);
329
330static struct timer_list slob_timer = TIMER_INITIALIZER(
331	(void (*)(unsigned long))kmem_cache_init, 0, 0);
332
333void kmem_cache_init(void)
334{
335	void *p = slob_alloc(PAGE_SIZE, 0, PAGE_SIZE-1);
336
337	if (p)
338		free_page((unsigned long)p);
339
340	mod_timer(&slob_timer, jiffies + HZ);
341}
342
343atomic_t slab_reclaim_pages = ATOMIC_INIT(0);
344EXPORT_SYMBOL(slab_reclaim_pages);
345
346#ifdef CONFIG_SMP
347
348void *__alloc_percpu(size_t size)
349{
350	int i;
351	struct percpu_data *pdata = kmalloc(sizeof (*pdata), GFP_KERNEL);
352
353	if (!pdata)
354		return NULL;
355
356	for_each_possible_cpu(i) {
357		pdata->ptrs[i] = kmalloc(size, GFP_KERNEL);
358		if (!pdata->ptrs[i])
359			goto unwind_oom;
360		memset(pdata->ptrs[i], 0, size);
361	}
362
363	/* Catch derefs w/o wrappers */
364	return (void *) (~(unsigned long) pdata);
365
366unwind_oom:
367	while (--i >= 0) {
368		if (!cpu_possible(i))
369			continue;
370		kfree(pdata->ptrs[i]);
371	}
372	kfree(pdata);
373	return NULL;
374}
375EXPORT_SYMBOL(__alloc_percpu);
376
377void
378free_percpu(const void *objp)
379{
380	int i;
381	struct percpu_data *p = (struct percpu_data *) (~(unsigned long) objp);
382
383	for_each_possible_cpu(i)
384		kfree(p->ptrs[i]);
385
386	kfree(p);
387}
388EXPORT_SYMBOL(free_percpu);
389
390#endif
391