diff options
Diffstat (limited to 'lib/idr.c')
| -rw-r--r-- | lib/idr.c | 379 |
1 files changed, 203 insertions, 176 deletions
diff --git a/lib/idr.c b/lib/idr.c index 9a366b5be2c2..3c20ad9b0463 100644 --- a/lib/idr.c +++ b/lib/idr.c @@ -6,8 +6,6 @@ #include <linux/spinlock.h> #include <linux/xarray.h> -DEFINE_PER_CPU(struct ida_bitmap *, ida_bitmap); - /** * idr_alloc_u32() - Allocate an ID. * @idr: IDR handle. @@ -320,6 +318,9 @@ EXPORT_SYMBOL(idr_replace); * free the individual IDs in it. You can use ida_is_empty() to find * out whether the IDA has any IDs currently allocated. * + * The IDA handles its own locking. It is safe to call any of the IDA + * functions without synchronisation in your code. + * * IDs are currently limited to the range [0-INT_MAX]. If this is an awkward * limitation, it should be quite straightforward to raise the maximum. */ @@ -327,151 +328,197 @@ EXPORT_SYMBOL(idr_replace); /* * Developer's notes: * - * The IDA uses the functionality provided by the IDR & radix tree to store - * bitmaps in each entry. The IDR_FREE tag means there is at least one bit - * free, unlike the IDR where it means at least one entry is free. + * The IDA uses the functionality provided by the XArray to store bitmaps in + * each entry. The XA_FREE_MARK is only cleared when all bits in the bitmap + * have been set. * - * I considered telling the radix tree that each slot is an order-10 node - * and storing the bit numbers in the radix tree, but the radix tree can't - * allow a single multiorder entry at index 0, which would significantly - * increase memory consumption for the IDA. So instead we divide the index - * by the number of bits in the leaf bitmap before doing a radix tree lookup. + * I considered telling the XArray that each slot is an order-10 node + * and indexing by bit number, but the XArray can't allow a single multi-index + * entry in the head, which would significantly increase memory consumption + * for the IDA. So instead we divide the index by the number of bits in the + * leaf bitmap before doing a radix tree lookup. * * As an optimisation, if there are only a few low bits set in any given * leaf, instead of allocating a 128-byte bitmap, we store the bits - * directly in the entry. - * - * We allow the radix tree 'exceptional' count to get out of date. Nothing - * in the IDA nor the radix tree code checks it. If it becomes important - * to maintain an accurate exceptional count, switch the rcu_assign_pointer() - * calls to radix_tree_iter_replace() which will correct the exceptional - * count. - * - * The IDA always requires a lock to alloc/free. If we add a 'test_bit' + * as a value entry. Value entries never have the XA_FREE_MARK cleared + * because we can always convert them into a bitmap entry. + * + * It would be possible to optimise further; once we've run out of a + * single 128-byte bitmap, we currently switch to a 576-byte node, put + * the 128-byte bitmap in the first entry and then start allocating extra + * 128-byte entries. We could instead use the 512 bytes of the node's + * data as a bitmap before moving to that scheme. I do not believe this + * is a worthwhile optimisation; Rasmus Villemoes surveyed the current + * users of the IDA and almost none of them use more than 1024 entries. + * Those that do use more than the 8192 IDs that the 512 bytes would + * provide. + * + * The IDA always uses a lock to alloc/free. If we add a 'test_bit' * equivalent, it will still need locking. Going to RCU lookup would require * using RCU to free bitmaps, and that's not trivial without embedding an * RCU head in the bitmap, which adds a 2-pointer overhead to each 128-byte * bitmap, which is excessive. */ -#define IDA_MAX (0x80000000U / IDA_BITMAP_BITS - 1) - -static int ida_get_new_above(struct ida *ida, int start) +/** + * ida_alloc_range() - Allocate an unused ID. + * @ida: IDA handle. + * @min: Lowest ID to allocate. + * @max: Highest ID to allocate. + * @gfp: Memory allocation flags. + * + * Allocate an ID between @min and @max, inclusive. The allocated ID will + * not exceed %INT_MAX, even if @max is larger. + * + * Context: Any context. + * Return: The allocated ID, or %-ENOMEM if memory could not be allocated, + * or %-ENOSPC if there are no free IDs. + */ +int ida_alloc_range(struct ida *ida, unsigned int min, unsigned int max, + gfp_t gfp) { - struct radix_tree_root *root = &ida->ida_rt; - void __rcu **slot; - struct radix_tree_iter iter; - struct ida_bitmap *bitmap; - unsigned long index; - unsigned bit; - int new; - - index = start / IDA_BITMAP_BITS; - bit = start % IDA_BITMAP_BITS; - - slot = radix_tree_iter_init(&iter, index); - for (;;) { - if (slot) - slot = radix_tree_next_slot(slot, &iter, - RADIX_TREE_ITER_TAGGED); - if (!slot) { - slot = idr_get_free(root, &iter, GFP_NOWAIT, IDA_MAX); - if (IS_ERR(slot)) { - if (slot == ERR_PTR(-ENOMEM)) - return -EAGAIN; - return PTR_ERR(slot); + XA_STATE(xas, &ida->xa, min / IDA_BITMAP_BITS); + unsigned bit = min % IDA_BITMAP_BITS; + unsigned long flags; + struct ida_bitmap *bitmap, *alloc = NULL; + + if ((int)min < 0) + return -ENOSPC; + + if ((int)max < 0) + max = INT_MAX; + +retry: + xas_lock_irqsave(&xas, flags); +next: + bitmap = xas_find_marked(&xas, max / IDA_BITMAP_BITS, XA_FREE_MARK); + if (xas.xa_index > min / IDA_BITMAP_BITS) + bit = 0; + if (xas.xa_index * IDA_BITMAP_BITS + bit > max) + goto nospc; + + if (xa_is_value(bitmap)) { + unsigned long tmp = xa_to_value(bitmap); + + if (bit < BITS_PER_XA_VALUE) { + bit = find_next_zero_bit(&tmp, BITS_PER_XA_VALUE, bit); + if (xas.xa_index * IDA_BITMAP_BITS + bit > max) + goto nospc; + if (bit < BITS_PER_XA_VALUE) { + tmp |= 1UL << bit; + xas_store(&xas, xa_mk_value(tmp)); + goto out; } } - if (iter.index > index) - bit = 0; - new = iter.index * IDA_BITMAP_BITS; - bitmap = rcu_dereference_raw(*slot); - if (xa_is_value(bitmap)) { - unsigned long tmp = xa_to_value(bitmap); - int vbit = find_next_zero_bit(&tmp, BITS_PER_XA_VALUE, - bit); - if (vbit < BITS_PER_XA_VALUE) { - tmp |= 1UL << vbit; - rcu_assign_pointer(*slot, xa_mk_value(tmp)); - return new + vbit; - } - bitmap = this_cpu_xchg(ida_bitmap, NULL); - if (!bitmap) - return -EAGAIN; - bitmap->bitmap[0] = tmp; - rcu_assign_pointer(*slot, bitmap); + bitmap = alloc; + if (!bitmap) + bitmap = kzalloc(sizeof(*bitmap), GFP_NOWAIT); + if (!bitmap) + goto alloc; + bitmap->bitmap[0] = tmp; + xas_store(&xas, bitmap); + if (xas_error(&xas)) { + bitmap->bitmap[0] = 0; + goto out; } + } - if (bitmap) { - bit = find_next_zero_bit(bitmap->bitmap, - IDA_BITMAP_BITS, bit); - new += bit; - if (new < 0) - return -ENOSPC; - if (bit == IDA_BITMAP_BITS) - continue; + if (bitmap) { + bit = find_next_zero_bit(bitmap->bitmap, IDA_BITMAP_BITS, bit); + if (xas.xa_index * IDA_BITMAP_BITS + bit > max) + goto nospc; + if (bit == IDA_BITMAP_BITS) + goto next; - __set_bit(bit, bitmap->bitmap); - if (bitmap_full(bitmap->bitmap, IDA_BITMAP_BITS)) - radix_tree_iter_tag_clear(root, &iter, - IDR_FREE); + __set_bit(bit, bitmap->bitmap); + if (bitmap_full(bitmap->bitmap, IDA_BITMAP_BITS)) + xas_clear_mark(&xas, XA_FREE_MARK); + } else { + if (bit < BITS_PER_XA_VALUE) { + bitmap = xa_mk_value(1UL << bit); } else { - new += bit; - if (new < 0) - return -ENOSPC; - if (bit < BITS_PER_XA_VALUE) { - bitmap = xa_mk_value(1UL << bit); - } else { - bitmap = this_cpu_xchg(ida_bitmap, NULL); - if (!bitmap) - return -EAGAIN; - __set_bit(bit, bitmap->bitmap); - } - radix_tree_iter_replace(root, &iter, slot, bitmap); + bitmap = alloc; + if (!bitmap) + bitmap = kzalloc(sizeof(*bitmap), GFP_NOWAIT); + if (!bitmap) + goto alloc; + __set_bit(bit, bitmap->bitmap); } - - return new; + xas_store(&xas, bitmap); + } +out: + xas_unlock_irqrestore(&xas, flags); + if (xas_nomem(&xas, gfp)) { + xas.xa_index = min / IDA_BITMAP_BITS; + bit = min % IDA_BITMAP_BITS; + goto retry; } + if (bitmap != alloc) + kfree(alloc); + if (xas_error(&xas)) + return xas_error(&xas); + return xas.xa_index * IDA_BITMAP_BITS + bit; +alloc: + xas_unlock_irqrestore(&xas, flags); + alloc = kzalloc(sizeof(*bitmap), gfp); + if (!alloc) + return -ENOMEM; + xas_set(&xas, min / IDA_BITMAP_BITS); + bit = min % IDA_BITMAP_BITS; + goto retry; +nospc: + xas_unlock_irqrestore(&xas, flags); + return -ENOSPC; } +EXPORT_SYMBOL(ida_alloc_range); -static void ida_remove(struct ida *ida, int id) +/** + * ida_free() - Release an allocated ID. + * @ida: IDA handle. + * @id: Previously allocated ID. + * + * Context: Any context. + */ +void ida_free(struct ida *ida, unsigned int id) { - unsigned long index = id / IDA_BITMAP_BITS; - unsigned offset = id % IDA_BITMAP_BITS; + XA_STATE(xas, &ida->xa, id / IDA_BITMAP_BITS); + unsigned bit = id % IDA_BITMAP_BITS; struct ida_bitmap *bitmap; - unsigned long *btmp; - struct radix_tree_iter iter; - void __rcu **slot; + unsigned long flags; - slot = radix_tree_iter_lookup(&ida->ida_rt, &iter, index); - if (!slot) - goto err; + BUG_ON((int)id < 0); + + xas_lock_irqsave(&xas, flags); + bitmap = xas_load(&xas); - bitmap = rcu_dereference_raw(*slot); if (xa_is_value(bitmap)) { - btmp = (unsigned long *)slot; - offset += 1; /* Intimate knowledge of the value encoding */ - if (offset >= BITS_PER_LONG) + unsigned long v = xa_to_value(bitmap); + if (bit >= BITS_PER_XA_VALUE) + goto err; + if (!(v & (1UL << bit))) goto err; + v &= ~(1UL << bit); + if (!v) + goto delete; + xas_store(&xas, xa_mk_value(v)); } else { - btmp = bitmap->bitmap; - } - if (!test_bit(offset, btmp)) - goto err; - - __clear_bit(offset, btmp); - radix_tree_iter_tag_set(&ida->ida_rt, &iter, IDR_FREE); - if (xa_is_value(bitmap)) { - if (xa_to_value(rcu_dereference_raw(*slot)) == 0) - radix_tree_iter_delete(&ida->ida_rt, &iter, slot); - } else if (bitmap_empty(btmp, IDA_BITMAP_BITS)) { - kfree(bitmap); - radix_tree_iter_delete(&ida->ida_rt, &iter, slot); + if (!test_bit(bit, bitmap->bitmap)) + goto err; + __clear_bit(bit, bitmap->bitmap); + xas_set_mark(&xas, XA_FREE_MARK); + if (bitmap_empty(bitmap->bitmap, IDA_BITMAP_BITS)) { + kfree(bitmap); +delete: + xas_store(&xas, NULL); + } } + xas_unlock_irqrestore(&xas, flags); return; err: + xas_unlock_irqrestore(&xas, flags); WARN(1, "ida_free called for id=%d which is not allocated.\n", id); } +EXPORT_SYMBOL(ida_free); /** * ida_destroy() - Free all IDs. @@ -486,80 +533,60 @@ static void ida_remove(struct ida *ida, int id) */ void ida_destroy(struct ida *ida) { + XA_STATE(xas, &ida->xa, 0); + struct ida_bitmap *bitmap; unsigned long flags; - struct radix_tree_iter iter; - void __rcu **slot; - xa_lock_irqsave(&ida->ida_rt, flags); - radix_tree_for_each_slot(slot, &ida->ida_rt, &iter, 0) { - struct ida_bitmap *bitmap = rcu_dereference_raw(*slot); + xas_lock_irqsave(&xas, flags); + xas_for_each(&xas, bitmap, ULONG_MAX) { if (!xa_is_value(bitmap)) kfree(bitmap); - radix_tree_iter_delete(&ida->ida_rt, &iter, slot); + xas_store(&xas, NULL); } - xa_unlock_irqrestore(&ida->ida_rt, flags); + xas_unlock_irqrestore(&xas, flags); } EXPORT_SYMBOL(ida_destroy); -/** - * ida_alloc_range() - Allocate an unused ID. - * @ida: IDA handle. - * @min: Lowest ID to allocate. - * @max: Highest ID to allocate. - * @gfp: Memory allocation flags. - * - * Allocate an ID between @min and @max, inclusive. The allocated ID will - * not exceed %INT_MAX, even if @max is larger. - * - * Context: Any context. - * Return: The allocated ID, or %-ENOMEM if memory could not be allocated, - * or %-ENOSPC if there are no free IDs. - */ -int ida_alloc_range(struct ida *ida, unsigned int min, unsigned int max, - gfp_t gfp) -{ - int id = 0; - unsigned long flags; - - if ((int)min < 0) - return -ENOSPC; +#ifndef __KERNEL__ +extern void xa_dump_index(unsigned long index, unsigned int shift); +#define IDA_CHUNK_SHIFT ilog2(IDA_BITMAP_BITS) - if ((int)max < 0) - max = INT_MAX; - -again: - xa_lock_irqsave(&ida->ida_rt, flags); - id = ida_get_new_above(ida, min); - if (id > (int)max) { - ida_remove(ida, id); - id = -ENOSPC; - } - xa_unlock_irqrestore(&ida->ida_rt, flags); +static void ida_dump_entry(void *entry, unsigned long index) +{ + unsigned long i; + + if (!entry) + return; + + if (xa_is_node(entry)) { + struct xa_node *node = xa_to_node(entry); + unsigned int shift = node->shift + IDA_CHUNK_SHIFT + + XA_CHUNK_SHIFT; + + xa_dump_index(index * IDA_BITMAP_BITS, shift); + xa_dump_node(node); + for (i = 0; i < XA_CHUNK_SIZE; i++) + ida_dump_entry(node->slots[i], + index | (i << node->shift)); + } else if (xa_is_value(entry)) { + xa_dump_index(index * IDA_BITMAP_BITS, ilog2(BITS_PER_LONG)); + pr_cont("value: data %lx [%px]\n", xa_to_value(entry), entry); + } else { + struct ida_bitmap *bitmap = entry; - if (unlikely(id == -EAGAIN)) { - if (!ida_pre_get(ida, gfp)) - return -ENOMEM; - goto again; + xa_dump_index(index * IDA_BITMAP_BITS, IDA_CHUNK_SHIFT); + pr_cont("bitmap: %p data", bitmap); + for (i = 0; i < IDA_BITMAP_LONGS; i++) + pr_cont(" %lx", bitmap->bitmap[i]); + pr_cont("\n"); } - - return id; } -EXPORT_SYMBOL(ida_alloc_range); -/** - * ida_free() - Release an allocated ID. - * @ida: IDA handle. - * @id: Previously allocated ID. - * - * Context: Any context. - */ -void ida_free(struct ida *ida, unsigned int id) +static void ida_dump(struct ida *ida) { - unsigned long flags; - - BUG_ON((int)id < 0); - xa_lock_irqsave(&ida->ida_rt, flags); - ida_remove(ida, id); - xa_unlock_irqrestore(&ida->ida_rt, flags); + struct xarray *xa = &ida->xa; + pr_debug("ida: %p node %p free %d\n", ida, xa->xa_head, + xa->xa_flags >> ROOT_TAG_SHIFT); + ida_dump_entry(xa->xa_head, 0); } -EXPORT_SYMBOL(ida_free); +#endif |