/*
* Fast and scalable bitmaps.
*
* Copyright (C) 2016 Facebook
* Copyright (C) 2013-2014 Jens Axboe
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public
* License v2 as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
#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 {
/**
* @word: The bitmap word itself.
*/
unsigned long word;
/**
* @depth: Number of bits being used in @word.
*/
unsigned long depth;
} ____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;
/**
* @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);
/**
* sbitmap_any_bit_clear() - Check for an unset bit in a &struct
* sbitmap.
* @sb: Bitmap to check.
*
* Return: true if any bit in the bitmap is clear, false otherwise.
*/
bool sbitmap_any_bit_clear(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) {
struct sbitmap_word *word = &sb->map[index];
unsigned int depth = min_t(unsigned int, word->depth - nr,
sb->depth - scanned);
scanned += depth;
if (!word->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->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));
}
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));
}
unsigned int sbitmap_weight(const struct sbitmap *sb);
/**
* 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);
#endif /* __LINUX_SCALE_BITMAP_H */
