/*
   * SLOB Allocator: Simple List Of Blocks
   *
   * Matt Mackall <mpm@selenic.com> 12/30/03
   *
   * How SLOB works:
   *
   * The core of SLOB is a traditional K&R style heap allocator, with
   * support for returning aligned objects. The granularity of this
   * allocator is 8 bytes on x86, though it's perhaps possible to reduce
   * this to 4 if it's deemed worth the effort. The slob heap is a
   * singly-linked list of pages from __get_free_page, grown on demand
   * and allocation from the heap is currently first-fit.
   *
   * Above this is an implementation of kmalloc/kfree. Blocks returned
   * from kmalloc are 8-byte aligned and prepended with a 8-byte header.
   * If kmalloc is asked for objects of PAGE_SIZE or larger, it calls
   * __get_free_pages directly so that it can return page-aligned blocks
   * and keeps a linked list of such pages and their orders. These
   * objects are detected in kfree() by their page alignment.
   *
   * SLAB is emulated on top of SLOB by simply calling constructors and
   * destructors for every SLAB allocation. Objects are returned with

   * the 8-byte alignment unless the SLAB_HWCACHE_ALIGN flag is

   * set, in which case the low-level allocator will fragment blocks to
   * create the proper alignment. Again, objects of page-size or greater
   * are allocated by calling __get_free_pages. As SLAB objects know
   * their size, no separate size bookkeeping is necessary and there is
   * essentially no allocation space overhead.
   */

  #include <linux/slab.h>
  #include <linux/mm.h>
  #include <linux/cache.h>
  #include <linux/init.h>
  #include <linux/module.h>
  #include <linux/timer.h>

  #include <linux/rcupdate.h>

  
  struct slob_block {
  	int units;
  	struct slob_block *next;
  };
  typedef struct slob_block slob_t;
  
  #define SLOB_UNIT sizeof(slob_t)
  #define SLOB_UNITS(size) (((size) + SLOB_UNIT - 1)/SLOB_UNIT)
  #define SLOB_ALIGN L1_CACHE_BYTES
  
  struct bigblock {
  	int order;
  	void *pages;
  	struct bigblock *next;
  };
  typedef struct bigblock bigblock_t;

  /*
   * struct slob_rcu is inserted at the tail of allocated slob blocks, which
   * were created with a SLAB_DESTROY_BY_RCU slab. slob_rcu is used to free
   * the block using call_rcu.
   */
  struct slob_rcu {
  	struct rcu_head head;
  	int size;
  };

  static slob_t arena = { .next = &arena, .units = 1 };
  static slob_t *slobfree = &arena;
  static bigblock_t *bigblocks;
  static DEFINE_SPINLOCK(slob_lock);
  static DEFINE_SPINLOCK(block_lock);
  
  static void slob_free(void *b, int size);

  static void slob_timer_cbk(void);

  
  static void *slob_alloc(size_t size, gfp_t gfp, int align)
  {
  	slob_t *prev, *cur, *aligned = 0;
  	int delta = 0, units = SLOB_UNITS(size);
  	unsigned long flags;
  
  	spin_lock_irqsave(&slob_lock, flags);
  	prev = slobfree;
  	for (cur = prev->next; ; prev = cur, cur = cur->next) {
  		if (align) {
  			aligned = (slob_t *)ALIGN((unsigned long)cur, align);
  			delta = aligned - cur;
  		}
  		if (cur->units >= units + delta) { /* room enough? */
  			if (delta) { /* need to fragment head to align? */
  				aligned->units = cur->units - delta;
  				aligned->next = cur->next;
  				cur->next = aligned;
  				cur->units = delta;
  				prev = cur;
  				cur = aligned;
  			}
  
  			if (cur->units == units) /* exact fit? */
  				prev->next = cur->next; /* unlink */
  			else { /* fragment */
  				prev->next = cur + units;
  				prev->next->units = cur->units - units;
  				prev->next->next = cur->next;
  				cur->units = units;
  			}
  
  			slobfree = prev;
  			spin_unlock_irqrestore(&slob_lock, flags);
  			return cur;
  		}
  		if (cur == slobfree) {
  			spin_unlock_irqrestore(&slob_lock, flags);
  
  			if (size == PAGE_SIZE) /* trying to shrink arena? */
  				return 0;
  
  			cur = (slob_t *)__get_free_page(gfp);
  			if (!cur)
  				return 0;
  
  			slob_free(cur, PAGE_SIZE);
  			spin_lock_irqsave(&slob_lock, flags);
  			cur = slobfree;
  		}
  	}
  }
  
  static void slob_free(void *block, int size)
  {
  	slob_t *cur, *b = (slob_t *)block;
  	unsigned long flags;
  
  	if (!block)
  		return;
  
  	if (size)
  		b->units = SLOB_UNITS(size);
  
  	/* Find reinsertion point */
  	spin_lock_irqsave(&slob_lock, flags);
  	for (cur = slobfree; !(b > cur && b < cur->next); cur = cur->next)
  		if (cur >= cur->next && (b > cur || b < cur->next))
  			break;
  
  	if (b + b->units == cur->next) {
  		b->units += cur->next->units;
  		b->next = cur->next->next;
  	} else
  		b->next = cur->next;
  
  	if (cur + cur->units == b) {
  		cur->units += b->units;
  		cur->next = b->next;
  	} else
  		cur->next = b;
  
  	slobfree = cur;
  
  	spin_unlock_irqrestore(&slob_lock, flags);
  }

  void *__kmalloc(size_t size, gfp_t gfp)

  {
  	slob_t *m;
  	bigblock_t *bb;
  	unsigned long flags;
  
  	if (size < PAGE_SIZE - SLOB_UNIT) {
  		m = slob_alloc(size + SLOB_UNIT, gfp, 0);
  		return m ? (void *)(m + 1) : 0;
  	}
  
  	bb = slob_alloc(sizeof(bigblock_t), gfp, 0);
  	if (!bb)
  		return 0;

  	bb->order = get_order(size);

  	bb->pages = (void *)__get_free_pages(gfp, bb->order);
  
  	if (bb->pages) {
  		spin_lock_irqsave(&block_lock, flags);
  		bb->next = bigblocks;
  		bigblocks = bb;
  		spin_unlock_irqrestore(&block_lock, flags);
  		return bb->pages;
  	}
  
  	slob_free(bb, sizeof(bigblock_t));
  	return 0;
  }

  EXPORT_SYMBOL(__kmalloc);

  /**
   * krealloc - reallocate memory. The contents will remain unchanged.
   *
   * @p: object to reallocate memory for.
   * @new_size: how many bytes of memory are required.
   * @flags: the type of memory to allocate.
   *
   * The contents of the object pointed to are preserved up to the
   * lesser of the new and old sizes.  If @p is %NULL, krealloc()
   * behaves exactly like kmalloc().  If @size is 0 and @p is not a
   * %NULL pointer, the object pointed to is freed.
   */
  void *krealloc(const void *p, size_t new_size, gfp_t flags)
  {
  	void *ret;
  
  	if (unlikely(!p))
  		return kmalloc_track_caller(new_size, flags);
  
  	if (unlikely(!new_size)) {
  		kfree(p);
  		return NULL;
  	}
  
  	ret = kmalloc_track_caller(new_size, flags);
  	if (ret) {
  		memcpy(ret, p, min(new_size, ksize(p)));
  		kfree(p);
  	}
  	return ret;
  }
  EXPORT_SYMBOL(krealloc);

  void kfree(const void *block)
  {
  	bigblock_t *bb, **last = &bigblocks;
  	unsigned long flags;
  
  	if (!block)
  		return;
  
  	if (!((unsigned long)block & (PAGE_SIZE-1))) {
  		/* might be on the big block list */
  		spin_lock_irqsave(&block_lock, flags);
  		for (bb = bigblocks; bb; last = &bb->next, bb = bb->next) {
  			if (bb->pages == block) {
  				*last = bb->next;
  				spin_unlock_irqrestore(&block_lock, flags);
  				free_pages((unsigned long)block, bb->order);
  				slob_free(bb, sizeof(bigblock_t));
  				return;
  			}
  		}
  		spin_unlock_irqrestore(&block_lock, flags);
  	}
  
  	slob_free((slob_t *)block - 1, 0);
  	return;
  }
  
  EXPORT_SYMBOL(kfree);

  size_t ksize(const void *block)

  {
  	bigblock_t *bb;
  	unsigned long flags;
  
  	if (!block)
  		return 0;
  
  	if (!((unsigned long)block & (PAGE_SIZE-1))) {
  		spin_lock_irqsave(&block_lock, flags);
  		for (bb = bigblocks; bb; bb = bb->next)
  			if (bb->pages == block) {
  				spin_unlock_irqrestore(&slob_lock, flags);
  				return PAGE_SIZE << bb->order;
  			}
  		spin_unlock_irqrestore(&block_lock, flags);
  	}
  
  	return ((slob_t *)block - 1)->units * SLOB_UNIT;
  }
  
  struct kmem_cache {
  	unsigned int size, align;

  	unsigned long flags;

  	const char *name;
  	void (*ctor)(void *, struct kmem_cache *, unsigned long);

  };
  
  struct kmem_cache *kmem_cache_create(const char *name, size_t size,
  	size_t align, unsigned long flags,
  	void (*ctor)(void*, struct kmem_cache *, unsigned long),
  	void (*dtor)(void*, struct kmem_cache *, unsigned long))
  {
  	struct kmem_cache *c;
  
  	c = slob_alloc(sizeof(struct kmem_cache), flags, 0);
  
  	if (c) {
  		c->name = name;
  		c->size = size;

  		if (flags & SLAB_DESTROY_BY_RCU) {

  			/* leave room for rcu footer at the end of object */
  			c->size += sizeof(struct slob_rcu);
  		}
  		c->flags = flags;

  		c->ctor = ctor;

  		/* ignore alignment unless it's forced */

  		c->align = (flags & SLAB_HWCACHE_ALIGN) ? SLOB_ALIGN : 0;

  		if (c->align < align)
  			c->align = align;

  	} else if (flags & SLAB_PANIC)
  		panic("Cannot create slab cache %s
  ", name);

  
  	return c;
  }
  EXPORT_SYMBOL(kmem_cache_create);

  void kmem_cache_destroy(struct kmem_cache *c)

  {
  	slob_free(c, sizeof(struct kmem_cache));

  }
  EXPORT_SYMBOL(kmem_cache_destroy);
  
  void *kmem_cache_alloc(struct kmem_cache *c, gfp_t flags)
  {
  	void *b;
  
  	if (c->size < PAGE_SIZE)
  		b = slob_alloc(c->size, flags, c->align);
  	else

  		b = (void *)__get_free_pages(flags, get_order(c->size));

  
  	if (c->ctor)

  		c->ctor(b, c, 0);

  
  	return b;
  }
  EXPORT_SYMBOL(kmem_cache_alloc);

  void *kmem_cache_zalloc(struct kmem_cache *c, gfp_t flags)
  {
  	void *ret = kmem_cache_alloc(c, flags);
  	if (ret)
  		memset(ret, 0, c->size);
  
  	return ret;
  }
  EXPORT_SYMBOL(kmem_cache_zalloc);

  static void __kmem_cache_free(void *b, int size)

  {

  	if (size < PAGE_SIZE)
  		slob_free(b, size);

  	else

  		free_pages((unsigned long)b, get_order(size));
  }
  
  static void kmem_rcu_free(struct rcu_head *head)
  {
  	struct slob_rcu *slob_rcu = (struct slob_rcu *)head;
  	void *b = (void *)slob_rcu - (slob_rcu->size - sizeof(struct slob_rcu));
  
  	__kmem_cache_free(b, slob_rcu->size);
  }
  
  void kmem_cache_free(struct kmem_cache *c, void *b)
  {
  	if (unlikely(c->flags & SLAB_DESTROY_BY_RCU)) {
  		struct slob_rcu *slob_rcu;
  		slob_rcu = b + (c->size - sizeof(struct slob_rcu));
  		INIT_RCU_HEAD(&slob_rcu->head);
  		slob_rcu->size = c->size;
  		call_rcu(&slob_rcu->head, kmem_rcu_free);
  	} else {

  		__kmem_cache_free(b, c->size);
  	}

  }
  EXPORT_SYMBOL(kmem_cache_free);
  
  unsigned int kmem_cache_size(struct kmem_cache *c)
  {
  	return c->size;
  }
  EXPORT_SYMBOL(kmem_cache_size);
  
  const char *kmem_cache_name(struct kmem_cache *c)
  {
  	return c->name;
  }
  EXPORT_SYMBOL(kmem_cache_name);
  
  static struct timer_list slob_timer = TIMER_INITIALIZER(

  	(void (*)(unsigned long))slob_timer_cbk, 0, 0);

  int kmem_cache_shrink(struct kmem_cache *d)
  {
  	return 0;
  }
  EXPORT_SYMBOL(kmem_cache_shrink);

  int kmem_ptr_validate(struct kmem_cache *a, const void *b)

  {
  	return 0;
  }

  void __init kmem_cache_init(void)
  {
  	slob_timer_cbk();
  }
  
  static void slob_timer_cbk(void)

  {
  	void *p = slob_alloc(PAGE_SIZE, 0, PAGE_SIZE-1);
  
  	if (p)
  		free_page((unsigned long)p);
  
  	mod_timer(&slob_timer, jiffies + HZ);
  }