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: Tejun Heo <htejun@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Tejun Heo 2007-06-14 03:45:13 +09:00 committed by Greg Kroah-Hartman
parent e33ac8bdb0
commit 72dba584b6
2 changed files with 274 additions and 0 deletions

View file

@ -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__ */

245
lib/idr.c
View file

@ -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);