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Diffstat (limited to 'include/linux/sbitmap.h')
-rw-r--r-- | include/linux/sbitmap.h | 583 |
1 files changed, 583 insertions, 0 deletions
diff --git a/include/linux/sbitmap.h b/include/linux/sbitmap.h new file mode 100644 index 000000000..e40d019c3 --- /dev/null +++ b/include/linux/sbitmap.h @@ -0,0 +1,583 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Fast and scalable bitmaps. + * + * Copyright (C) 2016 Facebook + * Copyright (C) 2013-2014 Jens Axboe + */ + +#ifndef __LINUX_SCALE_BITMAP_H +#define __LINUX_SCALE_BITMAP_H + +#include <linux/kernel.h> +#include <linux/slab.h> + +struct seq_file; + +/** + * struct sbitmap_word - Word in a &struct sbitmap. + */ +struct sbitmap_word { + /** + * @depth: Number of bits being used in @word/@cleared + */ + unsigned long depth; + + /** + * @word: word holding free bits + */ + unsigned long word ____cacheline_aligned_in_smp; + + /** + * @cleared: word holding cleared bits + */ + unsigned long cleared ____cacheline_aligned_in_smp; + + /** + * @swap_lock: Held while swapping word <-> cleared + */ + spinlock_t swap_lock; +} ____cacheline_aligned_in_smp; + +/** + * struct sbitmap - Scalable bitmap. + * + * A &struct sbitmap is spread over multiple cachelines to avoid ping-pong. This + * trades off higher memory usage for better scalability. + */ +struct sbitmap { + /** + * @depth: Number of bits used in the whole bitmap. + */ + unsigned int depth; + + /** + * @shift: log2(number of bits used per word) + */ + unsigned int shift; + + /** + * @map_nr: Number of words (cachelines) being used for the bitmap. + */ + unsigned int map_nr; + + /** + * @map: Allocated bitmap. + */ + struct sbitmap_word *map; +}; + +#define SBQ_WAIT_QUEUES 8 +#define SBQ_WAKE_BATCH 8 + +/** + * struct sbq_wait_state - Wait queue in a &struct sbitmap_queue. + */ +struct sbq_wait_state { + /** + * @wait_cnt: Number of frees remaining before we wake up. + */ + atomic_t wait_cnt; + + /** + * @wait: Wait queue. + */ + wait_queue_head_t wait; +} ____cacheline_aligned_in_smp; + +/** + * struct sbitmap_queue - Scalable bitmap with the added ability to wait on free + * bits. + * + * A &struct sbitmap_queue uses multiple wait queues and rolling wakeups to + * avoid contention on the wait queue spinlock. This ensures that we don't hit a + * scalability wall when we run out of free bits and have to start putting tasks + * to sleep. + */ +struct sbitmap_queue { + /** + * @sb: Scalable bitmap. + */ + struct sbitmap sb; + + /* + * @alloc_hint: Cache of last successfully allocated or freed bit. + * + * This is per-cpu, which allows multiple users to stick to different + * cachelines until the map is exhausted. + */ + unsigned int __percpu *alloc_hint; + + /** + * @wake_batch: Number of bits which must be freed before we wake up any + * waiters. + */ + unsigned int wake_batch; + + /** + * @wake_index: Next wait queue in @ws to wake up. + */ + atomic_t wake_index; + + /** + * @ws: Wait queues. + */ + struct sbq_wait_state *ws; + + /* + * @ws_active: count of currently active ws waitqueues + */ + atomic_t ws_active; + + /** + * @round_robin: Allocate bits in strict round-robin order. + */ + bool round_robin; + + /** + * @min_shallow_depth: The minimum shallow depth which may be passed to + * sbitmap_queue_get_shallow() or __sbitmap_queue_get_shallow(). + */ + unsigned int min_shallow_depth; +}; + +/** + * sbitmap_init_node() - Initialize a &struct sbitmap on a specific memory node. + * @sb: Bitmap to initialize. + * @depth: Number of bits to allocate. + * @shift: Use 2^@shift bits per word in the bitmap; if a negative number if + * given, a good default is chosen. + * @flags: Allocation flags. + * @node: Memory node to allocate on. + * + * Return: Zero on success or negative errno on failure. + */ +int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift, + gfp_t flags, int node); + +/** + * sbitmap_free() - Free memory used by a &struct sbitmap. + * @sb: Bitmap to free. + */ +static inline void sbitmap_free(struct sbitmap *sb) +{ + kfree(sb->map); + sb->map = NULL; +} + +/** + * sbitmap_resize() - Resize a &struct sbitmap. + * @sb: Bitmap to resize. + * @depth: New number of bits to resize to. + * + * Doesn't reallocate anything. It's up to the caller to ensure that the new + * depth doesn't exceed the depth that the sb was initialized with. + */ +void sbitmap_resize(struct sbitmap *sb, unsigned int depth); + +/** + * sbitmap_get() - Try to allocate a free bit from a &struct sbitmap. + * @sb: Bitmap to allocate from. + * @alloc_hint: Hint for where to start searching for a free bit. + * @round_robin: If true, be stricter about allocation order; always allocate + * starting from the last allocated bit. This is less efficient + * than the default behavior (false). + * + * This operation provides acquire barrier semantics if it succeeds. + * + * Return: Non-negative allocated bit number if successful, -1 otherwise. + */ +int sbitmap_get(struct sbitmap *sb, unsigned int alloc_hint, bool round_robin); + +/** + * sbitmap_get_shallow() - Try to allocate a free bit from a &struct sbitmap, + * limiting the depth used from each word. + * @sb: Bitmap to allocate from. + * @alloc_hint: Hint for where to start searching for a free bit. + * @shallow_depth: The maximum number of bits to allocate from a single word. + * + * This rather specific operation allows for having multiple users with + * different allocation limits. E.g., there can be a high-priority class that + * uses sbitmap_get() and a low-priority class that uses sbitmap_get_shallow() + * with a @shallow_depth of (1 << (@sb->shift - 1)). Then, the low-priority + * class can only allocate half of the total bits in the bitmap, preventing it + * from starving out the high-priority class. + * + * Return: Non-negative allocated bit number if successful, -1 otherwise. + */ +int sbitmap_get_shallow(struct sbitmap *sb, unsigned int alloc_hint, + unsigned long shallow_depth); + +/** + * sbitmap_any_bit_set() - Check for a set bit in a &struct sbitmap. + * @sb: Bitmap to check. + * + * Return: true if any bit in the bitmap is set, false otherwise. + */ +bool sbitmap_any_bit_set(const struct sbitmap *sb); + +#define SB_NR_TO_INDEX(sb, bitnr) ((bitnr) >> (sb)->shift) +#define SB_NR_TO_BIT(sb, bitnr) ((bitnr) & ((1U << (sb)->shift) - 1U)) + +typedef bool (*sb_for_each_fn)(struct sbitmap *, unsigned int, void *); + +/** + * __sbitmap_for_each_set() - Iterate over each set bit in a &struct sbitmap. + * @start: Where to start the iteration. + * @sb: Bitmap to iterate over. + * @fn: Callback. Should return true to continue or false to break early. + * @data: Pointer to pass to callback. + * + * This is inline even though it's non-trivial so that the function calls to the + * callback will hopefully get optimized away. + */ +static inline void __sbitmap_for_each_set(struct sbitmap *sb, + unsigned int start, + sb_for_each_fn fn, void *data) +{ + unsigned int index; + unsigned int nr; + unsigned int scanned = 0; + + if (start >= sb->depth) + start = 0; + index = SB_NR_TO_INDEX(sb, start); + nr = SB_NR_TO_BIT(sb, start); + + while (scanned < sb->depth) { + unsigned long word; + unsigned int depth = min_t(unsigned int, + sb->map[index].depth - nr, + sb->depth - scanned); + + scanned += depth; + word = sb->map[index].word & ~sb->map[index].cleared; + if (!word) + goto next; + + /* + * On the first iteration of the outer loop, we need to add the + * bit offset back to the size of the word for find_next_bit(). + * On all other iterations, nr is zero, so this is a noop. + */ + depth += nr; + while (1) { + nr = find_next_bit(&word, depth, nr); + if (nr >= depth) + break; + if (!fn(sb, (index << sb->shift) + nr, data)) + return; + + nr++; + } +next: + nr = 0; + if (++index >= sb->map_nr) + index = 0; + } +} + +/** + * sbitmap_for_each_set() - Iterate over each set bit in a &struct sbitmap. + * @sb: Bitmap to iterate over. + * @fn: Callback. Should return true to continue or false to break early. + * @data: Pointer to pass to callback. + */ +static inline void sbitmap_for_each_set(struct sbitmap *sb, sb_for_each_fn fn, + void *data) +{ + __sbitmap_for_each_set(sb, 0, fn, data); +} + +static inline unsigned long *__sbitmap_word(struct sbitmap *sb, + unsigned int bitnr) +{ + return &sb->map[SB_NR_TO_INDEX(sb, bitnr)].word; +} + +/* Helpers equivalent to the operations in asm/bitops.h and linux/bitmap.h */ + +static inline void sbitmap_set_bit(struct sbitmap *sb, unsigned int bitnr) +{ + set_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr)); +} + +static inline void sbitmap_clear_bit(struct sbitmap *sb, unsigned int bitnr) +{ + clear_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr)); +} + +/* + * This one is special, since it doesn't actually clear the bit, rather it + * sets the corresponding bit in the ->cleared mask instead. Paired with + * the caller doing sbitmap_deferred_clear() if a given index is full, which + * will clear the previously freed entries in the corresponding ->word. + */ +static inline void sbitmap_deferred_clear_bit(struct sbitmap *sb, unsigned int bitnr) +{ + unsigned long *addr = &sb->map[SB_NR_TO_INDEX(sb, bitnr)].cleared; + + set_bit(SB_NR_TO_BIT(sb, bitnr), addr); +} + +static inline void sbitmap_clear_bit_unlock(struct sbitmap *sb, + unsigned int bitnr) +{ + clear_bit_unlock(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr)); +} + +static inline int sbitmap_test_bit(struct sbitmap *sb, unsigned int bitnr) +{ + return test_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr)); +} + +/** + * sbitmap_show() - Dump &struct sbitmap information to a &struct seq_file. + * @sb: Bitmap to show. + * @m: struct seq_file to write to. + * + * This is intended for debugging. The format may change at any time. + */ +void sbitmap_show(struct sbitmap *sb, struct seq_file *m); + +/** + * sbitmap_bitmap_show() - Write a hex dump of a &struct sbitmap to a &struct + * seq_file. + * @sb: Bitmap to show. + * @m: struct seq_file to write to. + * + * This is intended for debugging. The output isn't guaranteed to be internally + * consistent. + */ +void sbitmap_bitmap_show(struct sbitmap *sb, struct seq_file *m); + +/** + * sbitmap_queue_init_node() - Initialize a &struct sbitmap_queue on a specific + * memory node. + * @sbq: Bitmap queue to initialize. + * @depth: See sbitmap_init_node(). + * @shift: See sbitmap_init_node(). + * @round_robin: See sbitmap_get(). + * @flags: Allocation flags. + * @node: Memory node to allocate on. + * + * Return: Zero on success or negative errno on failure. + */ +int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth, + int shift, bool round_robin, gfp_t flags, int node); + +/** + * sbitmap_queue_free() - Free memory used by a &struct sbitmap_queue. + * + * @sbq: Bitmap queue to free. + */ +static inline void sbitmap_queue_free(struct sbitmap_queue *sbq) +{ + kfree(sbq->ws); + free_percpu(sbq->alloc_hint); + sbitmap_free(&sbq->sb); +} + +/** + * sbitmap_queue_resize() - Resize a &struct sbitmap_queue. + * @sbq: Bitmap queue to resize. + * @depth: New number of bits to resize to. + * + * Like sbitmap_resize(), this doesn't reallocate anything. It has to do + * some extra work on the &struct sbitmap_queue, so it's not safe to just + * resize the underlying &struct sbitmap. + */ +void sbitmap_queue_resize(struct sbitmap_queue *sbq, unsigned int depth); + +/** + * __sbitmap_queue_get() - Try to allocate a free bit from a &struct + * sbitmap_queue with preemption already disabled. + * @sbq: Bitmap queue to allocate from. + * + * Return: Non-negative allocated bit number if successful, -1 otherwise. + */ +int __sbitmap_queue_get(struct sbitmap_queue *sbq); + +/** + * __sbitmap_queue_get_shallow() - Try to allocate a free bit from a &struct + * sbitmap_queue, limiting the depth used from each word, with preemption + * already disabled. + * @sbq: Bitmap queue to allocate from. + * @shallow_depth: The maximum number of bits to allocate from a single word. + * See sbitmap_get_shallow(). + * + * If you call this, make sure to call sbitmap_queue_min_shallow_depth() after + * initializing @sbq. + * + * Return: Non-negative allocated bit number if successful, -1 otherwise. + */ +int __sbitmap_queue_get_shallow(struct sbitmap_queue *sbq, + unsigned int shallow_depth); + +/** + * sbitmap_queue_get() - Try to allocate a free bit from a &struct + * sbitmap_queue. + * @sbq: Bitmap queue to allocate from. + * @cpu: Output parameter; will contain the CPU we ran on (e.g., to be passed to + * sbitmap_queue_clear()). + * + * Return: Non-negative allocated bit number if successful, -1 otherwise. + */ +static inline int sbitmap_queue_get(struct sbitmap_queue *sbq, + unsigned int *cpu) +{ + int nr; + + *cpu = get_cpu(); + nr = __sbitmap_queue_get(sbq); + put_cpu(); + return nr; +} + +/** + * sbitmap_queue_get_shallow() - Try to allocate a free bit from a &struct + * sbitmap_queue, limiting the depth used from each word. + * @sbq: Bitmap queue to allocate from. + * @cpu: Output parameter; will contain the CPU we ran on (e.g., to be passed to + * sbitmap_queue_clear()). + * @shallow_depth: The maximum number of bits to allocate from a single word. + * See sbitmap_get_shallow(). + * + * If you call this, make sure to call sbitmap_queue_min_shallow_depth() after + * initializing @sbq. + * + * Return: Non-negative allocated bit number if successful, -1 otherwise. + */ +static inline int sbitmap_queue_get_shallow(struct sbitmap_queue *sbq, + unsigned int *cpu, + unsigned int shallow_depth) +{ + int nr; + + *cpu = get_cpu(); + nr = __sbitmap_queue_get_shallow(sbq, shallow_depth); + put_cpu(); + return nr; +} + +/** + * sbitmap_queue_min_shallow_depth() - Inform a &struct sbitmap_queue of the + * minimum shallow depth that will be used. + * @sbq: Bitmap queue in question. + * @min_shallow_depth: The minimum shallow depth that will be passed to + * sbitmap_queue_get_shallow() or __sbitmap_queue_get_shallow(). + * + * sbitmap_queue_clear() batches wakeups as an optimization. The batch size + * depends on the depth of the bitmap. Since the shallow allocation functions + * effectively operate with a different depth, the shallow depth must be taken + * into account when calculating the batch size. This function must be called + * with the minimum shallow depth that will be used. Failure to do so can result + * in missed wakeups. + */ +void sbitmap_queue_min_shallow_depth(struct sbitmap_queue *sbq, + unsigned int min_shallow_depth); + +/** + * sbitmap_queue_clear() - Free an allocated bit and wake up waiters on a + * &struct sbitmap_queue. + * @sbq: Bitmap to free from. + * @nr: Bit number to free. + * @cpu: CPU the bit was allocated on. + */ +void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr, + unsigned int cpu); + +static inline int sbq_index_inc(int index) +{ + return (index + 1) & (SBQ_WAIT_QUEUES - 1); +} + +static inline void sbq_index_atomic_inc(atomic_t *index) +{ + int old = atomic_read(index); + int new = sbq_index_inc(old); + atomic_cmpxchg(index, old, new); +} + +/** + * sbq_wait_ptr() - Get the next wait queue to use for a &struct + * sbitmap_queue. + * @sbq: Bitmap queue to wait on. + * @wait_index: A counter per "user" of @sbq. + */ +static inline struct sbq_wait_state *sbq_wait_ptr(struct sbitmap_queue *sbq, + atomic_t *wait_index) +{ + struct sbq_wait_state *ws; + + ws = &sbq->ws[atomic_read(wait_index)]; + sbq_index_atomic_inc(wait_index); + return ws; +} + +/** + * sbitmap_queue_wake_all() - Wake up everything waiting on a &struct + * sbitmap_queue. + * @sbq: Bitmap queue to wake up. + */ +void sbitmap_queue_wake_all(struct sbitmap_queue *sbq); + +/** + * sbitmap_queue_wake_up() - Wake up some of waiters in one waitqueue + * on a &struct sbitmap_queue. + * @sbq: Bitmap queue to wake up. + */ +void sbitmap_queue_wake_up(struct sbitmap_queue *sbq); + +/** + * sbitmap_queue_show() - Dump &struct sbitmap_queue information to a &struct + * seq_file. + * @sbq: Bitmap queue to show. + * @m: struct seq_file to write to. + * + * This is intended for debugging. The format may change at any time. + */ +void sbitmap_queue_show(struct sbitmap_queue *sbq, struct seq_file *m); + +struct sbq_wait { + struct sbitmap_queue *sbq; /* if set, sbq_wait is accounted */ + struct wait_queue_entry wait; +}; + +#define DEFINE_SBQ_WAIT(name) \ + struct sbq_wait name = { \ + .sbq = NULL, \ + .wait = { \ + .private = current, \ + .func = autoremove_wake_function, \ + .entry = LIST_HEAD_INIT((name).wait.entry), \ + } \ + } + +/* + * Wrapper around prepare_to_wait_exclusive(), which maintains some extra + * internal state. + */ +void sbitmap_prepare_to_wait(struct sbitmap_queue *sbq, + struct sbq_wait_state *ws, + struct sbq_wait *sbq_wait, int state); + +/* + * Must be paired with sbitmap_prepare_to_wait(). + */ +void sbitmap_finish_wait(struct sbitmap_queue *sbq, struct sbq_wait_state *ws, + struct sbq_wait *sbq_wait); + +/* + * Wrapper around add_wait_queue(), which maintains some extra internal state + */ +void sbitmap_add_wait_queue(struct sbitmap_queue *sbq, + struct sbq_wait_state *ws, + struct sbq_wait *sbq_wait); + +/* + * Must be paired with sbitmap_add_wait_queue() + */ +void sbitmap_del_wait_queue(struct sbq_wait *sbq_wait); + +#endif /* __LINUX_SCALE_BITMAP_H */ |