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>

1 files changed, 245 insertions, 0 deletions

diff --git a/lib/idr.c b/lib/idr.c
index 30b33e2e7a50..b98f01a2eb94 100644
--- a/lib/idr.c
+++ b/lib/idr.c
@@ -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);