/*
   * SLOB Allocator: Simple List Of Blocks
   *
   * Matt Mackall <mpm@selenic.com> 12/30/03
   *

   * NUMA support by Paul Mundt, 2007.
   *

   * 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 as little as 2 bytes, however typically most architectures
   * will require 4 bytes on 32-bit and 8 bytes on 64-bit.

   *

   * The slob heap is a set of linked list of pages from alloc_pages(),
   * and within each page, there is a singly-linked list of free blocks
   * (slob_t). The heap is grown on demand. To reduce fragmentation,
   * heap pages are segregated into three lists, with objects less than
   * 256 bytes, objects less than 1024 bytes, and all other objects.
   *
   * Allocation from heap involves first searching for a page with
   * sufficient free blocks (using a next-fit-like approach) followed by
   * a first-fit scan of the page. Deallocation inserts objects back
   * into the free list in address order, so this is effectively an
   * address-ordered first fit.

   *
   * Above this is an implementation of kmalloc/kfree. Blocks returned

   * from kmalloc are prepended with a 4-byte header with the kmalloc size.

   * If kmalloc is asked for objects of PAGE_SIZE or larger, it calls

   * alloc_pages() directly, allocating compound pages so the page order

   * does not have to be separately tracked, and also stores the exact
   * allocation size in page->private so that it can be used to accurately
   * provide ksize(). These objects are detected in kfree() because slob_page()
   * is false for them.

   *
   * SLAB is emulated on top of SLOB by simply calling constructors and

   * destructors for every SLAB allocation. Objects are returned with the
   * 4-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 alloc_pages(). As SLAB objects know their size, no separate

   * size bookkeeping is necessary and there is essentially no allocation

   * space overhead, and compound pages aren't needed for multi-page
   * allocations.

   *
   * NUMA support in SLOB is fairly simplistic, pushing most of the real
   * logic down to the page allocator, and simply doing the node accounting
   * on the upper levels. In the event that a node id is explicitly
   * provided, alloc_pages_node() with the specified node id is used
   * instead. The common case (or when the node id isn't explicitly provided)
   * will default to the current node, as per numa_node_id().
   *
   * Node aware pages are still inserted in to the global freelist, and
   * these are scanned for by matching against the node id encoded in the
   * page flags. As a result, block allocations that can be satisfied from
   * the freelist will only be done so on pages residing on the same node,
   * in order to prevent random node placement.

   */

  #include <linux/kernel.h>

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

  #include <linux/rcupdate.h>

  #include <linux/list.h>
  #include <asm/atomic.h>

  /*
   * slob_block has a field 'units', which indicates size of block if +ve,
   * or offset of next block if -ve (in SLOB_UNITs).
   *
   * Free blocks of size 1 unit simply contain the offset of the next block.
   * Those with larger size contain their size in the first SLOB_UNIT of
   * memory, and the offset of the next free block in the second SLOB_UNIT.
   */

  #if PAGE_SIZE <= (32767 * 2)

  typedef s16 slobidx_t;
  #else
  typedef s32 slobidx_t;
  #endif

  struct slob_block {

  	slobidx_t units;

  };

  typedef struct slob_block slob_t;

  /*
   * We use struct page fields to manage some slob allocation aspects,
   * however to avoid the horrible mess in include/linux/mm_types.h, we'll
   * just define our own struct page type variant here.
   */
  struct slob_page {
  	union {
  		struct {
  			unsigned long flags;	/* mandatory */
  			atomic_t _count;	/* mandatory */
  			slobidx_t units;	/* free units left in page */
  			unsigned long pad[2];
  			slob_t *free;		/* first free slob_t in page */
  			struct list_head list;	/* linked list of free pages */
  		};
  		struct page page;
  	};
  };
  static inline void struct_slob_page_wrong_size(void)
  { BUILD_BUG_ON(sizeof(struct slob_page) != sizeof(struct page)); }
  
  /*
   * free_slob_page: call before a slob_page is returned to the page allocator.
   */
  static inline void free_slob_page(struct slob_page *sp)
  {
  	reset_page_mapcount(&sp->page);
  	sp->page.mapping = NULL;
  }
  
  /*

   * All partially free slob pages go on these lists.

   */

  #define SLOB_BREAK1 256
  #define SLOB_BREAK2 1024
  static LIST_HEAD(free_slob_small);
  static LIST_HEAD(free_slob_medium);
  static LIST_HEAD(free_slob_large);

  
  /*
   * slob_page: True for all slob pages (false for bigblock pages)
   */
  static inline int slob_page(struct slob_page *sp)
  {

  	return PageSlobPage((struct page *)sp);

  }
  
  static inline void set_slob_page(struct slob_page *sp)
  {

  	__SetPageSlobPage((struct page *)sp);

  }
  
  static inline void clear_slob_page(struct slob_page *sp)
  {

  	__ClearPageSlobPage((struct page *)sp);

  }
  
  /*
   * slob_page_free: true for pages on free_slob_pages list.
   */
  static inline int slob_page_free(struct slob_page *sp)
  {

  	return PageSlobFree((struct page *)sp);

  }

  static void set_slob_page_free(struct slob_page *sp, struct list_head *list)

  {

  	list_add(&sp->list, list);

  	__SetPageSlobFree((struct page *)sp);

  }
  
  static inline void clear_slob_page_free(struct slob_page *sp)
  {
  	list_del(&sp->list);

  	__ClearPageSlobFree((struct page *)sp);

  }

  #define SLOB_UNIT sizeof(slob_t)
  #define SLOB_UNITS(size) (((size) + SLOB_UNIT - 1)/SLOB_UNIT)
  #define SLOB_ALIGN L1_CACHE_BYTES

  /*
   * 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;
  };

  /*
   * slob_lock protects all slob allocator structures.
   */

  static DEFINE_SPINLOCK(slob_lock);

  /*
   * Encode the given size and next info into a free slob block s.
   */
  static void set_slob(slob_t *s, slobidx_t size, slob_t *next)
  {
  	slob_t *base = (slob_t *)((unsigned long)s & PAGE_MASK);
  	slobidx_t offset = next - base;

  	if (size > 1) {
  		s[0].units = size;
  		s[1].units = offset;
  	} else
  		s[0].units = -offset;
  }

  /*
   * Return the size of a slob block.
   */
  static slobidx_t slob_units(slob_t *s)
  {
  	if (s->units > 0)
  		return s->units;
  	return 1;
  }
  
  /*
   * Return the next free slob block pointer after this one.
   */
  static slob_t *slob_next(slob_t *s)
  {
  	slob_t *base = (slob_t *)((unsigned long)s & PAGE_MASK);
  	slobidx_t next;
  
  	if (s[0].units < 0)
  		next = -s[0].units;
  	else
  		next = s[1].units;
  	return base+next;
  }
  
  /*
   * Returns true if s is the last free block in its page.
   */
  static int slob_last(slob_t *s)
  {
  	return !((unsigned long)slob_next(s) & ~PAGE_MASK);
  }

  static void *slob_new_page(gfp_t gfp, int order, int node)
  {
  	void *page;
  
  #ifdef CONFIG_NUMA
  	if (node != -1)
  		page = alloc_pages_node(node, gfp, order);
  	else
  #endif
  		page = alloc_pages(gfp, order);
  
  	if (!page)
  		return NULL;
  
  	return page_address(page);
  }

  /*
   * Allocate a slob block within a given slob_page sp.
   */
  static void *slob_page_alloc(struct slob_page *sp, size_t size, int align)

  {
  	slob_t *prev, *cur, *aligned = 0;
  	int delta = 0, units = SLOB_UNITS(size);

  	for (prev = NULL, cur = sp->free; ; prev = cur, cur = slob_next(cur)) {
  		slobidx_t avail = slob_units(cur);

  		if (align) {
  			aligned = (slob_t *)ALIGN((unsigned long)cur, align);
  			delta = aligned - cur;
  		}

  		if (avail >= units + delta) { /* room enough? */
  			slob_t *next;

  			if (delta) { /* need to fragment head to align? */

  				next = slob_next(cur);
  				set_slob(aligned, avail - delta, next);
  				set_slob(cur, delta, aligned);

  				prev = cur;
  				cur = aligned;

  				avail = slob_units(cur);

  			}

  			next = slob_next(cur);
  			if (avail == units) { /* exact fit? unlink. */
  				if (prev)
  					set_slob(prev, slob_units(prev), next);
  				else
  					sp->free = next;
  			} else { /* fragment */
  				if (prev)
  					set_slob(prev, slob_units(prev), cur + units);
  				else
  					sp->free = cur + units;
  				set_slob(cur + units, avail - units, next);

  			}

  			sp->units -= units;
  			if (!sp->units)
  				clear_slob_page_free(sp);

  			return cur;
  		}

  		if (slob_last(cur))
  			return NULL;
  	}
  }

  /*
   * slob_alloc: entry point into the slob allocator.
   */

  static void *slob_alloc(size_t size, gfp_t gfp, int align, int node)

  {
  	struct slob_page *sp;

  	struct list_head *prev;

  	struct list_head *slob_list;

  	slob_t *b = NULL;
  	unsigned long flags;

  	if (size < SLOB_BREAK1)
  		slob_list = &free_slob_small;
  	else if (size < SLOB_BREAK2)
  		slob_list = &free_slob_medium;
  	else
  		slob_list = &free_slob_large;

  	spin_lock_irqsave(&slob_lock, flags);
  	/* Iterate through each partially free page, try to find room */

  	list_for_each_entry(sp, slob_list, list) {

  #ifdef CONFIG_NUMA
  		/*
  		 * If there's a node specification, search for a partial
  		 * page with a matching node id in the freelist.
  		 */
  		if (node != -1 && page_to_nid(&sp->page) != node)
  			continue;
  #endif

  		/* Enough room on this page? */
  		if (sp->units < SLOB_UNITS(size))
  			continue;

  		/* Attempt to alloc */
  		prev = sp->list.prev;
  		b = slob_page_alloc(sp, size, align);
  		if (!b)
  			continue;
  
  		/* Improve fragment distribution and reduce our average
  		 * search time by starting our next search here. (see
  		 * Knuth vol 1, sec 2.5, pg 449) */

  		if (prev != slob_list->prev &&
  				slob_list->next != prev->next)
  			list_move_tail(slob_list, prev->next);

  		break;

  	}

  	spin_unlock_irqrestore(&slob_lock, flags);
  
  	/* Not enough space: must allocate a new page */
  	if (!b) {

  		b = slob_new_page(gfp & ~__GFP_ZERO, 0, node);

  		if (!b)
  			return 0;
  		sp = (struct slob_page *)virt_to_page(b);
  		set_slob_page(sp);
  
  		spin_lock_irqsave(&slob_lock, flags);
  		sp->units = SLOB_UNITS(PAGE_SIZE);
  		sp->free = b;
  		INIT_LIST_HEAD(&sp->list);
  		set_slob(b, SLOB_UNITS(PAGE_SIZE), b + SLOB_UNITS(PAGE_SIZE));

  		set_slob_page_free(sp, slob_list);

  		b = slob_page_alloc(sp, size, align);
  		BUG_ON(!b);
  		spin_unlock_irqrestore(&slob_lock, flags);
  	}

  	if (unlikely((gfp & __GFP_ZERO) && b))
  		memset(b, 0, size);

  	return b;

  }

  /*
   * slob_free: entry point into the slob allocator.
   */

  static void slob_free(void *block, int size)
  {

  	struct slob_page *sp;
  	slob_t *prev, *next, *b = (slob_t *)block;
  	slobidx_t units;

  	unsigned long flags;

  	if (unlikely(ZERO_OR_NULL_PTR(block)))

  		return;

  	BUG_ON(!size);

  	sp = (struct slob_page *)virt_to_page(block);
  	units = SLOB_UNITS(size);

  	spin_lock_irqsave(&slob_lock, flags);

  	if (sp->units + units == SLOB_UNITS(PAGE_SIZE)) {
  		/* Go directly to page allocator. Do not pass slob allocator */
  		if (slob_page_free(sp))
  			clear_slob_page_free(sp);
  		clear_slob_page(sp);
  		free_slob_page(sp);
  		free_page((unsigned long)b);
  		goto out;
  	}

  	if (!slob_page_free(sp)) {
  		/* This slob page is about to become partially free. Easy! */
  		sp->units = units;
  		sp->free = b;
  		set_slob(b, units,
  			(void *)((unsigned long)(b +
  					SLOB_UNITS(PAGE_SIZE)) & PAGE_MASK));

  		set_slob_page_free(sp, &free_slob_small);

  		goto out;
  	}
  
  	/*
  	 * Otherwise the page is already partially free, so find reinsertion
  	 * point.
  	 */
  	sp->units += units;

  	if (b < sp->free) {

  		if (b + units == sp->free) {
  			units += slob_units(sp->free);
  			sp->free = slob_next(sp->free);
  		}

  		set_slob(b, units, sp->free);
  		sp->free = b;
  	} else {
  		prev = sp->free;
  		next = slob_next(prev);
  		while (b > next) {
  			prev = next;
  			next = slob_next(prev);
  		}

  		if (!slob_last(prev) && b + units == next) {
  			units += slob_units(next);
  			set_slob(b, units, slob_next(next));
  		} else
  			set_slob(b, units, next);
  
  		if (prev + slob_units(prev) == b) {
  			units = slob_units(b) + slob_units(prev);
  			set_slob(prev, units, slob_next(b));
  		} else
  			set_slob(prev, slob_units(prev), b);
  	}
  out:

  	spin_unlock_irqrestore(&slob_lock, flags);
  }

  /*
   * End of slob allocator proper. Begin kmem_cache_alloc and kmalloc frontend.
   */

  #ifndef ARCH_KMALLOC_MINALIGN
  #define ARCH_KMALLOC_MINALIGN __alignof__(unsigned long)
  #endif
  
  #ifndef ARCH_SLAB_MINALIGN
  #define ARCH_SLAB_MINALIGN __alignof__(unsigned long)
  #endif

  void *__kmalloc_node(size_t size, gfp_t gfp, int node)

  {

  	unsigned int *m;

  	int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
  
  	if (size < PAGE_SIZE - align) {

  		if (!size)
  			return ZERO_SIZE_PTR;

  		m = slob_alloc(size + align, gfp, align, node);

  		if (!m)
  			return NULL;
  		*m = size;

  		return (void *)m + align;

  	} else {
  		void *ret;

  		ret = slob_new_page(gfp | __GFP_COMP, get_order(size), node);

  		if (ret) {
  			struct page *page;
  			page = virt_to_page(ret);
  			page->private = size;
  		}
  		return ret;

  	}

  }

  EXPORT_SYMBOL(__kmalloc_node);

  
  void kfree(const void *block)
  {

  	struct slob_page *sp;

  	if (unlikely(ZERO_OR_NULL_PTR(block)))

  		return;

  	sp = (struct slob_page *)virt_to_page(block);

  	if (slob_page(sp)) {

  		int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
  		unsigned int *m = (unsigned int *)(block - align);
  		slob_free(m, *m + align);

  	} else
  		put_page(&sp->page);

  }

  EXPORT_SYMBOL(kfree);

  /* can't use ksize for kmem_cache_alloc memory, only kmalloc */

  size_t ksize(const void *block)

  {

  	struct slob_page *sp;

  	BUG_ON(!block);
  	if (unlikely(block == ZERO_SIZE_PTR))

  		return 0;

  	sp = (struct slob_page *)virt_to_page(block);

  	if (slob_page(sp)) {
  		int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
  		unsigned int *m = (unsigned int *)(block - align);
  		return SLOB_UNITS(*m) * SLOB_UNIT;
  	} else

  		return sp->page.private;

  }
  
  struct kmem_cache {
  	unsigned int size, align;

  	unsigned long flags;

  	const char *name;

  	void (*ctor)(void *);

  };
  
  struct kmem_cache *kmem_cache_create(const char *name, size_t size,

  	size_t align, unsigned long flags, void (*ctor)(void *))

  {
  	struct kmem_cache *c;

  	c = slob_alloc(sizeof(struct kmem_cache),

  		GFP_KERNEL, ARCH_KMALLOC_MINALIGN, -1);

  
  	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 < ARCH_SLAB_MINALIGN)
  			c->align = ARCH_SLAB_MINALIGN;

  		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_node(struct kmem_cache *c, gfp_t flags, int node)

  {
  	void *b;
  
  	if (c->size < PAGE_SIZE)

  		b = slob_alloc(c->size, flags, c->align, node);

  	else

  		b = slob_new_page(flags, get_order(c->size), node);

  
  	if (c->ctor)

  		c->ctor(b);

  
  	return b;
  }

  EXPORT_SYMBOL(kmem_cache_alloc_node);

  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);

  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;
  }

  static unsigned int slob_ready __read_mostly;
  
  int slab_is_available(void)
  {
  	return slob_ready;
  }

  void __init kmem_cache_init(void)
  {

  	slob_ready = 1;

  }