Commit 72dba584 authored by Tejun Heo's avatar Tejun Heo Committed by Greg Kroah-Hartman
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ida: implement idr based id allocator 



Implement idr based id allocator.  ida is used the same way idr is
used but lacks id -> ptr translation and thus consumes much less
memory.  struct ida_bitmap is attached as leaf nodes to idr tree which
is managed by the idr code.  Each ida_bitmap is 128bytes long and
contains slightly less than a thousand slots.

ida is more aggressive with releasing extra resources acquired using
ida_pre_get().  After every successful id allocation, ida frees one
reserved idr_layer if possible.  Reserved ida_bitmap is not freed
automatically but only one ida_bitmap is reserved and it's almost
always used right away.  Under most circumstances, ida won't hold on
to memory for too long which isn't actively used.

Signed-off-by: default avatarTejun Heo <htejun@gmail.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent e33ac8bd

include/linux/idr.h

+29 −0
Original line number Diff line number Diff line
@@ -83,4 +83,33 @@ void idr_remove(struct idr *idp, int id); 
void idr_destroy(struct idr *idp);

void idr_init(struct idr *idp);





/*

 * IDA - IDR based id allocator, use when translation from id to

 * pointer isn't necessary.

 */

#define IDA_CHUNK_SIZE		128	/* 128 bytes per chunk */

#define IDA_BITMAP_LONGS	(128 / sizeof(long) - 1)

#define IDA_BITMAP_BITS		(IDA_BITMAP_LONGS * sizeof(long) * 8)



struct ida_bitmap {

	long			nr_busy;

	unsigned long		bitmap[IDA_BITMAP_LONGS];

};



struct ida {

	struct idr		idr;

	struct ida_bitmap	*free_bitmap;

};



#define IDA_INIT(name)		{ .idr = IDR_INIT(name), .free_bitmap = NULL, }

#define DEFINE_IDA(name)	struct ida name = IDA_INIT(name)



int ida_pre_get(struct ida *ida, gfp_t gfp_mask);

int ida_get_new_above(struct ida *ida, int starting_id, int *p_id);

int ida_get_new(struct ida *ida, int *p_id);

void ida_remove(struct ida *ida, int id);

void ida_destroy(struct ida *ida);

void ida_init(struct ida *ida);



#endif /* __IDR_H__ */

lib/idr.c

+245 −0
Original line number Diff line number Diff line
@@ -506,3 +506,248 @@ void idr_init(struct idr *idp) 
	spin_lock_init(&idp->lock);

}

EXPORT_SYMBOL(idr_init);





/*

 * IDA - IDR based ID allocator

 *

 * this is id allocator without id -> pointer translation.  Memory

 * usage is much lower than full blown idr because each id only

 * occupies a bit.  ida uses a custom leaf node which contains

 * IDA_BITMAP_BITS slots.

 *

 * 2007-04-25  written by Tejun Heo <htejun@gmail.com>

 */



static void free_bitmap(struct ida *ida, struct ida_bitmap *bitmap)

{

	unsigned long flags;



	if (!ida->free_bitmap) {

		spin_lock_irqsave(&ida->idr.lock, flags);

		if (!ida->free_bitmap) {

			ida->free_bitmap = bitmap;

			bitmap = NULL;

		}

		spin_unlock_irqrestore(&ida->idr.lock, flags);

	}



	kfree(bitmap);

}



/**

 * ida_pre_get - reserve resources for ida allocation

 * @ida:	ida handle

 * @gfp_mask:	memory allocation flag

 *

 * This function should be called prior to locking and calling the

 * following function.  It preallocates enough memory to satisfy the

 * worst possible allocation.

 *

 * If the system is REALLY out of memory this function returns 0,

 * otherwise 1.

 */

int ida_pre_get(struct ida *ida, gfp_t gfp_mask)

{

	/* allocate idr_layers */

	if (!idr_pre_get(&ida->idr, gfp_mask))

		return 0;



	/* allocate free_bitmap */

	if (!ida->free_bitmap) {

		struct ida_bitmap *bitmap;



		bitmap = kmalloc(sizeof(struct ida_bitmap), gfp_mask);

		if (!bitmap)

			return 0;



		free_bitmap(ida, bitmap);

	}



	return 1;

}

EXPORT_SYMBOL(ida_pre_get);



/**

 * ida_get_new_above - allocate new ID above or equal to a start id

 * @ida:	ida handle

 * @staring_id:	id to start search at

 * @p_id:	pointer to the allocated handle

 *

 * Allocate new ID above or equal to @ida.  It should be called with

 * any required locks.

 *

 * If memory is required, it will return -EAGAIN, you should unlock

 * and go back to the ida_pre_get() call.  If the ida is full, it will

 * return -ENOSPC.

 *

 * @p_id returns a value in the range 0 ... 0x7fffffff.

 */

int ida_get_new_above(struct ida *ida, int starting_id, int *p_id)

{

	struct idr_layer *pa[MAX_LEVEL];

	struct ida_bitmap *bitmap;

	unsigned long flags;

	int idr_id = starting_id / IDA_BITMAP_BITS;

	int offset = starting_id % IDA_BITMAP_BITS;

	int t, id;



 restart:

	/* get vacant slot */

	t = idr_get_empty_slot(&ida->idr, idr_id, pa);

	if (t < 0) {

		if (t == -1)

			return -EAGAIN;

		else /* will be -3 */

			return -ENOSPC;

	}



	if (t * IDA_BITMAP_BITS >= MAX_ID_BIT)

		return -ENOSPC;



	if (t != idr_id)

		offset = 0;

	idr_id = t;



	/* if bitmap isn't there, create a new one */

	bitmap = (void *)pa[0]->ary[idr_id & IDR_MASK];

	if (!bitmap) {

		spin_lock_irqsave(&ida->idr.lock, flags);

		bitmap = ida->free_bitmap;

		ida->free_bitmap = NULL;

		spin_unlock_irqrestore(&ida->idr.lock, flags);



		if (!bitmap)

			return -EAGAIN;



		memset(bitmap, 0, sizeof(struct ida_bitmap));

		pa[0]->ary[idr_id & IDR_MASK] = (void *)bitmap;

		pa[0]->count++;

	}



	/* lookup for empty slot */

	t = find_next_zero_bit(bitmap->bitmap, IDA_BITMAP_BITS, offset);

	if (t == IDA_BITMAP_BITS) {

		/* no empty slot after offset, continue to the next chunk */

		idr_id++;

		offset = 0;

		goto restart;

	}



	id = idr_id * IDA_BITMAP_BITS + t;

	if (id >= MAX_ID_BIT)

		return -ENOSPC;



	__set_bit(t, bitmap->bitmap);

	if (++bitmap->nr_busy == IDA_BITMAP_BITS)

		idr_mark_full(pa, idr_id);



	*p_id = id;



	/* Each leaf node can handle nearly a thousand slots and the

	 * whole idea of ida is to have small memory foot print.

	 * Throw away extra resources one by one after each successful

	 * allocation.

	 */

	if (ida->idr.id_free_cnt || ida->free_bitmap) {

		struct idr_layer *p = alloc_layer(&ida->idr);

		if (p)

			kmem_cache_free(idr_layer_cache, p);

	}



	return 0;

}

EXPORT_SYMBOL(ida_get_new_above);



/**

 * ida_get_new - allocate new ID

 * @ida:	idr handle

 * @p_id:	pointer to the allocated handle

 *

 * Allocate new ID.  It should be called with any required locks.

 *

 * If memory is required, it will return -EAGAIN, you should unlock

 * and go back to the idr_pre_get() call.  If the idr is full, it will

 * return -ENOSPC.

 *

 * @id returns a value in the range 0 ... 0x7fffffff.

 */

int ida_get_new(struct ida *ida, int *p_id)

{

	return ida_get_new_above(ida, 0, p_id);

}

EXPORT_SYMBOL(ida_get_new);



/**

 * ida_remove - remove the given ID

 * @ida:	ida handle

 * @id:		ID to free

 */

void ida_remove(struct ida *ida, int id)

{

	struct idr_layer *p = ida->idr.top;

	int shift = (ida->idr.layers - 1) * IDR_BITS;

	int idr_id = id / IDA_BITMAP_BITS;

	int offset = id % IDA_BITMAP_BITS;

	int n;

	struct ida_bitmap *bitmap;



	/* clear full bits while looking up the leaf idr_layer */

	while ((shift > 0) && p) {

		n = (idr_id >> shift) & IDR_MASK;

		__clear_bit(n, &p->bitmap);

		p = p->ary[n];

		shift -= IDR_BITS;

	}



	if (p == NULL)

		goto err;



	n = idr_id & IDR_MASK;

	__clear_bit(n, &p->bitmap);



	bitmap = (void *)p->ary[n];

	if (!test_bit(offset, bitmap->bitmap))

		goto err;



	/* update bitmap and remove it if empty */

	__clear_bit(offset, bitmap->bitmap);

	if (--bitmap->nr_busy == 0) {

		__set_bit(n, &p->bitmap);	/* to please idr_remove() */

		idr_remove(&ida->idr, idr_id);

		free_bitmap(ida, bitmap);

	}



	return;



 err:

	printk(KERN_WARNING

	       "ida_remove called for id=%d which is not allocated.\n", id);

}

EXPORT_SYMBOL(ida_remove);



/**

 * ida_destroy - release all cached layers within an ida tree

 * ida:		ida handle

 */

void ida_destroy(struct ida *ida)

{

	idr_destroy(&ida->idr);

	kfree(ida->free_bitmap);

}

EXPORT_SYMBOL(ida_destroy);



/**

 * ida_init - initialize ida handle

 * @ida:	ida handle

 *

 * This function is use to set up the handle (@ida) that you will pass

 * to the rest of the functions.

 */

void ida_init(struct ida *ida)

{

	memset(ida, 0, sizeof(struct ida));

	idr_init(&ida->idr);



}

EXPORT_SYMBOL(ida_init);

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