1 /*
2 * SLOB Allocator: Simple List Of Blocks
3 *
4 * Matt Mackall <mpm@selenic.com> 12/30/03
5 *
6 * NUMA support by Paul Mundt, 2007.
7 *
8 * How SLOB works:
9 *
10 * The core of SLOB is a traditional K&R style heap allocator, with
11 * support for returning aligned objects. The granularity of this
12 * allocator is as little as 2 bytes, however typically most architectures
13 * will require 4 bytes on 32-bit and 8 bytes on 64-bit.
14 *
15 * The slob heap is a set of linked list of pages from alloc_pages(),
16 * and within each page, there is a singly-linked list of free blocks
17 * (slob_t). The heap is grown on demand. To reduce fragmentation,
18 * heap pages are segregated into three lists, with objects less than
19 * 256 bytes, objects less than 1024 bytes, and all other objects.
20 *
21 * Allocation from heap involves first searching for a page with
22 * sufficient free blocks (using a next-fit-like approach) followed by
23 * a first-fit scan of the page. Deallocation inserts objects back
24 * into the free list in address order, so this is effectively an
25 * address-ordered first fit.
26 *
27 * Above this is an implementation of kmalloc/kfree. Blocks returned
28 * from kmalloc are prepended with a 4-byte header with the kmalloc size.
29 * If kmalloc is asked for objects of PAGE_SIZE or larger, it calls
30 * alloc_pages() directly, allocating compound pages so the page order
31 * does not have to be separately tracked, and also stores the exact
32 * allocation size in page->private so that it can be used to accurately
33 * provide ksize(). These objects are detected in kfree() because slob_page()
34 * is false for them.
35 *
36 * SLAB is emulated on top of SLOB by simply calling constructors and
37 * destructors for every SLAB allocation. Objects are returned with the
38 * 4-byte alignment unless the SLAB_HWCACHE_ALIGN flag is set, in which
39 * case the low-level allocator will fragment blocks to create the proper
40 * alignment. Again, objects of page-size or greater are allocated by
41 * calling alloc_pages(). As SLAB objects know their size, no separate
42 * size bookkeeping is necessary and there is essentially no allocation
43 * space overhead, and compound pages aren't needed for multi-page
44 * allocations.
45 *
46 * NUMA support in SLOB is fairly simplistic, pushing most of the real
47 * logic down to the page allocator, and simply doing the node accounting
48 * on the upper levels. In the event that a node id is explicitly
49 * provided, alloc_pages_node() with the specified node id is used
50 * instead. The common case (or when the node id isn't explicitly provided)
51 * will default to the current node, as per numa_node_id().
52 *
53 * Node aware pages are still inserted in to the global freelist, and
54 * these are scanned for by matching against the node id encoded in the
55 * page flags. As a result, block allocations that can be satisfied from
56 * the freelist will only be done so on pages residing on the same node,
57 * in order to prevent random node placement.
58 */
59
60 #include <linux/kernel.h>
61 #include <linux/slab.h>
62 #include <linux/mm.h>
63 #include <linux/cache.h>
64 #include <linux/init.h>
65 #include <linux/module.h>
66 #include <linux/rcupdate.h>
67 #include <linux/list.h>
68 #include <asm/atomic.h>
69
70 /*
71 * slob_block has a field 'units', which indicates size of block if +ve,
72 * or offset of next block if -ve (in SLOB_UNITs).
73 *
74 * Free blocks of size 1 unit simply contain the offset of the next block.
75 * Those with larger size contain their size in the first SLOB_UNIT of
76 * memory, and the offset of the next free block in the second SLOB_UNIT.
77 */
78 #if PAGE_SIZE <= (32767 * 2)
79 typedef s16 slobidx_t;
80 #else
81 typedef s32 slobidx_t;
82 #endif
83
84 struct slob_block {
85 slobidx_t units;
86 };
87 typedef struct slob_block slob_t;
88
89 /*
90 * We use struct page fields to manage some slob allocation aspects,
91 * however to avoid the horrible mess in include/linux/mm_types.h, we'll
92 * just define our own struct page type variant here.
93 */
94 struct slob_page {
95 union {
96 struct {
97 unsigned long flags; /* mandatory */
98 atomic_t _count; /* mandatory */
99 slobidx_t units; /* free units left in page */
100 unsigned long pad[2];
101 slob_t *free; /* first free slob_t in page */
102 struct list_head list; /* linked list of free pages */
103 };
104 struct page page;
105 };
106 };
struct_slob_page_wrong_size(void)107 static inline void struct_slob_page_wrong_size(void)
108 { BUILD_BUG_ON(sizeof(struct slob_page) != sizeof(struct page)); }
109
110 /*
111 * free_slob_page: call before a slob_page is returned to the page allocator.
112 */
free_slob_page(struct slob_page * sp)113 static inline void free_slob_page(struct slob_page *sp)
114 {
115 reset_page_mapcount(&sp->page);
116 sp->page.mapping = NULL;
117 }
118
119 /*
120 * All partially free slob pages go on these lists.
121 */
122 #define SLOB_BREAK1 256
123 #define SLOB_BREAK2 1024
124 static LIST_HEAD(free_slob_small);
125 static LIST_HEAD(free_slob_medium);
126 static LIST_HEAD(free_slob_large);
127
128 /*
129 * slob_page: True for all slob pages (false for bigblock pages)
130 */
slob_page(struct slob_page * sp)131 static inline int slob_page(struct slob_page *sp)
132 {
133 return PageSlobPage((struct page *)sp);
134 }
135
set_slob_page(struct slob_page * sp)136 static inline void set_slob_page(struct slob_page *sp)
137 {
138 __SetPageSlobPage((struct page *)sp);
139 }
140
clear_slob_page(struct slob_page * sp)141 static inline void clear_slob_page(struct slob_page *sp)
142 {
143 __ClearPageSlobPage((struct page *)sp);
144 }
145
146 /*
147 * slob_page_free: true for pages on free_slob_pages list.
148 */
slob_page_free(struct slob_page * sp)149 static inline int slob_page_free(struct slob_page *sp)
150 {
151 return PageSlobFree((struct page *)sp);
152 }
153
set_slob_page_free(struct slob_page * sp,struct list_head * list)154 static void set_slob_page_free(struct slob_page *sp, struct list_head *list)
155 {
156 list_add(&sp->list, list);
157 __SetPageSlobFree((struct page *)sp);
158 }
159
clear_slob_page_free(struct slob_page * sp)160 static inline void clear_slob_page_free(struct slob_page *sp)
161 {
162 list_del(&sp->list);
163 __ClearPageSlobFree((struct page *)sp);
164 }
165
166 #define SLOB_UNIT sizeof(slob_t)
167 #define SLOB_UNITS(size) (((size) + SLOB_UNIT - 1)/SLOB_UNIT)
168 #define SLOB_ALIGN L1_CACHE_BYTES
169
170 /*
171 * struct slob_rcu is inserted at the tail of allocated slob blocks, which
172 * were created with a SLAB_DESTROY_BY_RCU slab. slob_rcu is used to free
173 * the block using call_rcu.
174 */
175 struct slob_rcu {
176 struct rcu_head head;
177 int size;
178 };
179
180 /*
181 * slob_lock protects all slob allocator structures.
182 */
183 static DEFINE_SPINLOCK(slob_lock);
184
185 /*
186 * Encode the given size and next info into a free slob block s.
187 */
set_slob(slob_t * s,slobidx_t size,slob_t * next)188 static void set_slob(slob_t *s, slobidx_t size, slob_t *next)
189 {
190 slob_t *base = (slob_t *)((unsigned long)s & PAGE_MASK);
191 slobidx_t offset = next - base;
192
193 if (size > 1) {
194 s[0].units = size;
195 s[1].units = offset;
196 } else
197 s[0].units = -offset;
198 }
199
200 /*
201 * Return the size of a slob block.
202 */
slob_units(slob_t * s)203 static slobidx_t slob_units(slob_t *s)
204 {
205 if (s->units > 0)
206 return s->units;
207 return 1;
208 }
209
210 /*
211 * Return the next free slob block pointer after this one.
212 */
slob_next(slob_t * s)213 static slob_t *slob_next(slob_t *s)
214 {
215 slob_t *base = (slob_t *)((unsigned long)s & PAGE_MASK);
216 slobidx_t next;
217
218 if (s[0].units < 0)
219 next = -s[0].units;
220 else
221 next = s[1].units;
222 return base+next;
223 }
224
225 /*
226 * Returns true if s is the last free block in its page.
227 */
slob_last(slob_t * s)228 static int slob_last(slob_t *s)
229 {
230 return !((unsigned long)slob_next(s) & ~PAGE_MASK);
231 }
232
slob_new_page(gfp_t gfp,int order,int node)233 static void *slob_new_page(gfp_t gfp, int order, int node)
234 {
235 void *page;
236
237 #ifdef CONFIG_NUMA
238 if (node != -1)
239 page = alloc_pages_node(node, gfp, order);
240 else
241 #endif
242 page = alloc_pages(gfp, order);
243
244 if (!page)
245 return NULL;
246
247 return page_address(page);
248 }
249
250 /*
251 * Allocate a slob block within a given slob_page sp.
252 */
slob_page_alloc(struct slob_page * sp,size_t size,int align)253 static void *slob_page_alloc(struct slob_page *sp, size_t size, int align)
254 {
255 slob_t *prev, *cur, *aligned = 0;
256 int delta = 0, units = SLOB_UNITS(size);
257
258 for (prev = NULL, cur = sp->free; ; prev = cur, cur = slob_next(cur)) {
259 slobidx_t avail = slob_units(cur);
260
261 if (align) {
262 aligned = (slob_t *)ALIGN((unsigned long)cur, align);
263 delta = aligned - cur;
264 }
265 if (avail >= units + delta) { /* room enough? */
266 slob_t *next;
267
268 if (delta) { /* need to fragment head to align? */
269 next = slob_next(cur);
270 set_slob(aligned, avail - delta, next);
271 set_slob(cur, delta, aligned);
272 prev = cur;
273 cur = aligned;
274 avail = slob_units(cur);
275 }
276
277 next = slob_next(cur);
278 if (avail == units) { /* exact fit? unlink. */
279 if (prev)
280 set_slob(prev, slob_units(prev), next);
281 else
282 sp->free = next;
283 } else { /* fragment */
284 if (prev)
285 set_slob(prev, slob_units(prev), cur + units);
286 else
287 sp->free = cur + units;
288 set_slob(cur + units, avail - units, next);
289 }
290
291 sp->units -= units;
292 if (!sp->units)
293 clear_slob_page_free(sp);
294 return cur;
295 }
296 if (slob_last(cur))
297 return NULL;
298 }
299 }
300
301 /*
302 * slob_alloc: entry point into the slob allocator.
303 */
slob_alloc(size_t size,gfp_t gfp,int align,int node)304 static void *slob_alloc(size_t size, gfp_t gfp, int align, int node)
305 {
306 struct slob_page *sp;
307 struct list_head *prev;
308 struct list_head *slob_list;
309 slob_t *b = NULL;
310 unsigned long flags;
311
312 if (size < SLOB_BREAK1)
313 slob_list = &free_slob_small;
314 else if (size < SLOB_BREAK2)
315 slob_list = &free_slob_medium;
316 else
317 slob_list = &free_slob_large;
318
319 spin_lock_irqsave(&slob_lock, flags);
320 /* Iterate through each partially free page, try to find room */
321 list_for_each_entry(sp, slob_list, list) {
322 #ifdef CONFIG_NUMA
323 /*
324 * If there's a node specification, search for a partial
325 * page with a matching node id in the freelist.
326 */
327 if (node != -1 && page_to_nid(&sp->page) != node)
328 continue;
329 #endif
330 /* Enough room on this page? */
331 if (sp->units < SLOB_UNITS(size))
332 continue;
333
334 /* Attempt to alloc */
335 prev = sp->list.prev;
336 b = slob_page_alloc(sp, size, align);
337 if (!b)
338 continue;
339
340 /* Improve fragment distribution and reduce our average
341 * search time by starting our next search here. (see
342 * Knuth vol 1, sec 2.5, pg 449) */
343 if (prev != slob_list->prev &&
344 slob_list->next != prev->next)
345 list_move_tail(slob_list, prev->next);
346 break;
347 }
348 spin_unlock_irqrestore(&slob_lock, flags);
349
350 /* Not enough space: must allocate a new page */
351 if (!b) {
352 b = slob_new_page(gfp & ~__GFP_ZERO, 0, node);
353 if (!b)
354 return 0;
355 sp = (struct slob_page *)virt_to_page(b);
356 set_slob_page(sp);
357
358 spin_lock_irqsave(&slob_lock, flags);
359 sp->units = SLOB_UNITS(PAGE_SIZE);
360 sp->free = b;
361 INIT_LIST_HEAD(&sp->list);
362 set_slob(b, SLOB_UNITS(PAGE_SIZE), b + SLOB_UNITS(PAGE_SIZE));
363 set_slob_page_free(sp, slob_list);
364 b = slob_page_alloc(sp, size, align);
365 BUG_ON(!b);
366 spin_unlock_irqrestore(&slob_lock, flags);
367 }
368 if (unlikely((gfp & __GFP_ZERO) && b))
369 memset(b, 0, size);
370 return b;
371 }
372
373 /*
374 * slob_free: entry point into the slob allocator.
375 */
slob_free(void * block,int size)376 static void slob_free(void *block, int size)
377 {
378 struct slob_page *sp;
379 slob_t *prev, *next, *b = (slob_t *)block;
380 slobidx_t units;
381 unsigned long flags;
382
383 if (unlikely(ZERO_OR_NULL_PTR(block)))
384 return;
385 BUG_ON(!size);
386
387 sp = (struct slob_page *)virt_to_page(block);
388 units = SLOB_UNITS(size);
389
390 spin_lock_irqsave(&slob_lock, flags);
391
392 if (sp->units + units == SLOB_UNITS(PAGE_SIZE)) {
393 /* Go directly to page allocator. Do not pass slob allocator */
394 if (slob_page_free(sp))
395 clear_slob_page_free(sp);
396 clear_slob_page(sp);
397 free_slob_page(sp);
398 free_page((unsigned long)b);
399 goto out;
400 }
401
402 if (!slob_page_free(sp)) {
403 /* This slob page is about to become partially free. Easy! */
404 sp->units = units;
405 sp->free = b;
406 set_slob(b, units,
407 (void *)((unsigned long)(b +
408 SLOB_UNITS(PAGE_SIZE)) & PAGE_MASK));
409 set_slob_page_free(sp, &free_slob_small);
410 goto out;
411 }
412
413 /*
414 * Otherwise the page is already partially free, so find reinsertion
415 * point.
416 */
417 sp->units += units;
418
419 if (b < sp->free) {
420 if (b + units == sp->free) {
421 units += slob_units(sp->free);
422 sp->free = slob_next(sp->free);
423 }
424 set_slob(b, units, sp->free);
425 sp->free = b;
426 } else {
427 prev = sp->free;
428 next = slob_next(prev);
429 while (b > next) {
430 prev = next;
431 next = slob_next(prev);
432 }
433
434 if (!slob_last(prev) && b + units == next) {
435 units += slob_units(next);
436 set_slob(b, units, slob_next(next));
437 } else
438 set_slob(b, units, next);
439
440 if (prev + slob_units(prev) == b) {
441 units = slob_units(b) + slob_units(prev);
442 set_slob(prev, units, slob_next(b));
443 } else
444 set_slob(prev, slob_units(prev), b);
445 }
446 out:
447 spin_unlock_irqrestore(&slob_lock, flags);
448 }
449
450 /*
451 * End of slob allocator proper. Begin kmem_cache_alloc and kmalloc frontend.
452 */
453
454 #ifndef ARCH_KMALLOC_MINALIGN
455 #define ARCH_KMALLOC_MINALIGN __alignof__(unsigned long)
456 #endif
457
458 #ifndef ARCH_SLAB_MINALIGN
459 #define ARCH_SLAB_MINALIGN __alignof__(unsigned long)
460 #endif
461
__kmalloc_node(size_t size,gfp_t gfp,int node)462 void *__kmalloc_node(size_t size, gfp_t gfp, int node)
463 {
464 unsigned int *m;
465 int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
466
467 if (size < PAGE_SIZE - align) {
468 if (!size)
469 return ZERO_SIZE_PTR;
470
471 m = slob_alloc(size + align, gfp, align, node);
472 if (!m)
473 return NULL;
474 *m = size;
475 return (void *)m + align;
476 } else {
477 void *ret;
478
479 ret = slob_new_page(gfp | __GFP_COMP, get_order(size), node);
480 if (ret) {
481 struct page *page;
482 page = virt_to_page(ret);
483 page->private = size;
484 }
485 return ret;
486 }
487 }
488 EXPORT_SYMBOL(__kmalloc_node);
489
kfree(const void * block)490 void kfree(const void *block)
491 {
492 struct slob_page *sp;
493
494 if (unlikely(ZERO_OR_NULL_PTR(block)))
495 return;
496
497 sp = (struct slob_page *)virt_to_page(block);
498 if (slob_page(sp)) {
499 int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
500 unsigned int *m = (unsigned int *)(block - align);
501 slob_free(m, *m + align);
502 } else
503 put_page(&sp->page);
504 }
505 EXPORT_SYMBOL(kfree);
506
507 /* can't use ksize for kmem_cache_alloc memory, only kmalloc */
ksize(const void * block)508 size_t ksize(const void *block)
509 {
510 struct slob_page *sp;
511
512 BUG_ON(!block);
513 if (unlikely(block == ZERO_SIZE_PTR))
514 return 0;
515
516 sp = (struct slob_page *)virt_to_page(block);
517 if (slob_page(sp)) {
518 int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
519 unsigned int *m = (unsigned int *)(block - align);
520 return SLOB_UNITS(*m) * SLOB_UNIT;
521 } else
522 return sp->page.private;
523 }
524 EXPORT_SYMBOL(ksize);
525
526 struct kmem_cache {
527 unsigned int size, align;
528 unsigned long flags;
529 const char *name;
530 void (*ctor)(void *);
531 };
532
kmem_cache_create(const char * name,size_t size,size_t align,unsigned long flags,void (* ctor)(void *))533 struct kmem_cache *kmem_cache_create(const char *name, size_t size,
534 size_t align, unsigned long flags, void (*ctor)(void *))
535 {
536 struct kmem_cache *c;
537
538 c = slob_alloc(sizeof(struct kmem_cache),
539 GFP_KERNEL, ARCH_KMALLOC_MINALIGN, -1);
540
541 if (c) {
542 c->name = name;
543 c->size = size;
544 if (flags & SLAB_DESTROY_BY_RCU) {
545 /* leave room for rcu footer at the end of object */
546 c->size += sizeof(struct slob_rcu);
547 }
548 c->flags = flags;
549 c->ctor = ctor;
550 /* ignore alignment unless it's forced */
551 c->align = (flags & SLAB_HWCACHE_ALIGN) ? SLOB_ALIGN : 0;
552 if (c->align < ARCH_SLAB_MINALIGN)
553 c->align = ARCH_SLAB_MINALIGN;
554 if (c->align < align)
555 c->align = align;
556 } else if (flags & SLAB_PANIC)
557 panic("Cannot create slab cache %s\n", name);
558
559 return c;
560 }
561 EXPORT_SYMBOL(kmem_cache_create);
562
kmem_cache_destroy(struct kmem_cache * c)563 void kmem_cache_destroy(struct kmem_cache *c)
564 {
565 slob_free(c, sizeof(struct kmem_cache));
566 }
567 EXPORT_SYMBOL(kmem_cache_destroy);
568
kmem_cache_alloc_node(struct kmem_cache * c,gfp_t flags,int node)569 void *kmem_cache_alloc_node(struct kmem_cache *c, gfp_t flags, int node)
570 {
571 void *b;
572
573 if (c->size < PAGE_SIZE)
574 b = slob_alloc(c->size, flags, c->align, node);
575 else
576 b = slob_new_page(flags, get_order(c->size), node);
577
578 if (c->ctor)
579 c->ctor(b);
580
581 return b;
582 }
583 EXPORT_SYMBOL(kmem_cache_alloc_node);
584
__kmem_cache_free(void * b,int size)585 static void __kmem_cache_free(void *b, int size)
586 {
587 if (size < PAGE_SIZE)
588 slob_free(b, size);
589 else
590 free_pages((unsigned long)b, get_order(size));
591 }
592
kmem_rcu_free(struct rcu_head * head)593 static void kmem_rcu_free(struct rcu_head *head)
594 {
595 struct slob_rcu *slob_rcu = (struct slob_rcu *)head;
596 void *b = (void *)slob_rcu - (slob_rcu->size - sizeof(struct slob_rcu));
597
598 __kmem_cache_free(b, slob_rcu->size);
599 }
600
kmem_cache_free(struct kmem_cache * c,void * b)601 void kmem_cache_free(struct kmem_cache *c, void *b)
602 {
603 if (unlikely(c->flags & SLAB_DESTROY_BY_RCU)) {
604 struct slob_rcu *slob_rcu;
605 slob_rcu = b + (c->size - sizeof(struct slob_rcu));
606 INIT_RCU_HEAD(&slob_rcu->head);
607 slob_rcu->size = c->size;
608 call_rcu(&slob_rcu->head, kmem_rcu_free);
609 } else {
610 __kmem_cache_free(b, c->size);
611 }
612 }
613 EXPORT_SYMBOL(kmem_cache_free);
614
kmem_cache_size(struct kmem_cache * c)615 unsigned int kmem_cache_size(struct kmem_cache *c)
616 {
617 return c->size;
618 }
619 EXPORT_SYMBOL(kmem_cache_size);
620
kmem_cache_name(struct kmem_cache * c)621 const char *kmem_cache_name(struct kmem_cache *c)
622 {
623 return c->name;
624 }
625 EXPORT_SYMBOL(kmem_cache_name);
626
kmem_cache_shrink(struct kmem_cache * d)627 int kmem_cache_shrink(struct kmem_cache *d)
628 {
629 return 0;
630 }
631 EXPORT_SYMBOL(kmem_cache_shrink);
632
kmem_ptr_validate(struct kmem_cache * a,const void * b)633 int kmem_ptr_validate(struct kmem_cache *a, const void *b)
634 {
635 return 0;
636 }
637
638 static unsigned int slob_ready __read_mostly;
639
slab_is_available(void)640 int slab_is_available(void)
641 {
642 return slob_ready;
643 }
644
kmem_cache_init(void)645 void __init kmem_cache_init(void)
646 {
647 slob_ready = 1;
648 }
649