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blk-mq: abstract tag allocation out into sbitmap library
This is a generally useful data structure, so make it available to anyone else who might want to use it. It's also a nice cleanup separating the allocation logic from the rest of the tag handling logic. The code is behind a new Kconfig option, CONFIG_SBITMAP, which is only selected by CONFIG_BLOCK for now. This should be a complete noop functionality-wise. Signed-off-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Omar Sandoval
Jens Axboe
parent
703fd1c0f1
commit
88459642cb
11 changed files with 789 additions and 476 deletions
327
include/linux/sbitmap.h
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327
include/linux/sbitmap.h
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/*
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* Fast and scalable bitmaps.
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*
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* Copyright (C) 2016 Facebook
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* Copyright (C) 2013-2014 Jens Axboe
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public
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* License v2 as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <https://www.gnu.org/licenses/>.
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*/
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#ifndef __LINUX_SCALE_BITMAP_H
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#define __LINUX_SCALE_BITMAP_H
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#include <linux/kernel.h>
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#include <linux/slab.h>
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/**
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* struct sbitmap_word - Word in a &struct sbitmap.
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*/
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struct sbitmap_word {
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/**
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* @word: The bitmap word itself.
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*/
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unsigned long word;
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/**
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* @depth: Number of bits being used in @word.
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*/
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unsigned long depth;
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} ____cacheline_aligned_in_smp;
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/**
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* struct sbitmap - Scalable bitmap.
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*
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* A &struct sbitmap is spread over multiple cachelines to avoid ping-pong. This
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* trades off higher memory usage for better scalability.
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*/
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struct sbitmap {
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/**
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* @depth: Number of bits used in the whole bitmap.
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*/
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unsigned int depth;
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/**
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* @shift: log2(number of bits used per word)
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*/
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unsigned int shift;
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/**
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* @map_nr: Number of words (cachelines) being used for the bitmap.
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*/
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unsigned int map_nr;
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/**
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* @map: Allocated bitmap.
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*/
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struct sbitmap_word *map;
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};
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#define SBQ_WAIT_QUEUES 8
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#define SBQ_WAKE_BATCH 8
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/**
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* struct sbq_wait_state - Wait queue in a &struct sbitmap_queue.
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*/
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struct sbq_wait_state {
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/**
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* @wait_cnt: Number of frees remaining before we wake up.
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*/
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atomic_t wait_cnt;
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/**
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* @wait: Wait queue.
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*/
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wait_queue_head_t wait;
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} ____cacheline_aligned_in_smp;
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/**
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* struct sbitmap_queue - Scalable bitmap with the added ability to wait on free
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* bits.
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*
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* A &struct sbitmap_queue uses multiple wait queues and rolling wakeups to
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* avoid contention on the wait queue spinlock. This ensures that we don't hit a
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* scalability wall when we run out of free bits and have to start putting tasks
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* to sleep.
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*/
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struct sbitmap_queue {
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/**
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* @sb: Scalable bitmap.
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*/
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struct sbitmap sb;
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/**
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* @wake_batch: Number of bits which must be freed before we wake up any
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* waiters.
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*/
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unsigned int wake_batch;
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/**
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* @wake_index: Next wait queue in @ws to wake up.
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*/
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atomic_t wake_index;
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/**
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* @ws: Wait queues.
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*/
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struct sbq_wait_state *ws;
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};
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/**
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* sbitmap_init_node() - Initialize a &struct sbitmap on a specific memory node.
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* @sb: Bitmap to initialize.
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* @depth: Number of bits to allocate.
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* @shift: Use 2^@shift bits per word in the bitmap; if a negative number if
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* given, a good default is chosen.
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* @flags: Allocation flags.
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* @node: Memory node to allocate on.
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*
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* Return: Zero on success or negative errno on failure.
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*/
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int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
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gfp_t flags, int node);
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/**
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* sbitmap_free() - Free memory used by a &struct sbitmap.
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* @sb: Bitmap to free.
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*/
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static inline void sbitmap_free(struct sbitmap *sb)
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{
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kfree(sb->map);
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sb->map = NULL;
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}
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/**
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* sbitmap_resize() - Resize a &struct sbitmap.
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* @sb: Bitmap to resize.
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* @depth: New number of bits to resize to.
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*
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* Doesn't reallocate anything. It's up to the caller to ensure that the new
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* depth doesn't exceed the depth that the sb was initialized with.
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*/
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void sbitmap_resize(struct sbitmap *sb, unsigned int depth);
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/**
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* sbitmap_get() - Try to allocate a free bit from a &struct sbitmap.
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* @sb: Bitmap to allocate from.
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* @alloc_hint: Hint for where to start searching for a free bit.
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* @round_robin: If true, be stricter about allocation order; always allocate
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* starting from the last allocated bit. This is less efficient
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* than the default behavior (false).
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*
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* Return: Non-negative allocated bit number if successful, -1 otherwise.
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*/
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int sbitmap_get(struct sbitmap *sb, unsigned int alloc_hint, bool round_robin);
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/**
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* sbitmap_any_bit_set() - Check for a set bit in a &struct sbitmap.
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* @sb: Bitmap to check.
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*
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* Return: true if any bit in the bitmap is set, false otherwise.
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*/
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bool sbitmap_any_bit_set(const struct sbitmap *sb);
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/**
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* sbitmap_any_bit_clear() - Check for an unset bit in a &struct
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* sbitmap.
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* @sb: Bitmap to check.
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*
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* Return: true if any bit in the bitmap is clear, false otherwise.
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*/
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bool sbitmap_any_bit_clear(const struct sbitmap *sb);
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typedef bool (*sb_for_each_fn)(struct sbitmap *, unsigned int, void *);
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/**
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* sbitmap_for_each_set() - Iterate over each set bit in a &struct sbitmap.
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* @sb: Bitmap to iterate over.
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* @fn: Callback. Should return true to continue or false to break early.
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* @data: Pointer to pass to callback.
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*
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* This is inline even though it's non-trivial so that the function calls to the
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* callback will hopefully get optimized away.
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*/
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static inline void sbitmap_for_each_set(struct sbitmap *sb, sb_for_each_fn fn,
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void *data)
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{
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unsigned int i;
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for (i = 0; i < sb->map_nr; i++) {
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struct sbitmap_word *word = &sb->map[i];
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unsigned int off, nr;
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if (!word->word)
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continue;
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nr = 0;
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off = i << sb->shift;
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while (1) {
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nr = find_next_bit(&word->word, word->depth, nr);
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if (nr >= word->depth)
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break;
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if (!fn(sb, off + nr, data))
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return;
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nr++;
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}
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}
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}
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#define SB_NR_TO_INDEX(sb, bitnr) ((bitnr) >> (sb)->shift)
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#define SB_NR_TO_BIT(sb, bitnr) ((bitnr) & ((1U << (sb)->shift) - 1U))
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static inline unsigned long *__sbitmap_word(struct sbitmap *sb,
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unsigned int bitnr)
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{
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return &sb->map[SB_NR_TO_INDEX(sb, bitnr)].word;
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}
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/* Helpers equivalent to the operations in asm/bitops.h and linux/bitmap.h */
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static inline void sbitmap_set_bit(struct sbitmap *sb, unsigned int bitnr)
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{
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set_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr));
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}
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static inline void sbitmap_clear_bit(struct sbitmap *sb, unsigned int bitnr)
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{
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clear_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr));
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}
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static inline int sbitmap_test_bit(struct sbitmap *sb, unsigned int bitnr)
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{
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return test_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr));
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}
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unsigned int sbitmap_weight(const struct sbitmap *sb);
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/**
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* sbitmap_queue_init_node() - Initialize a &struct sbitmap_queue on a specific
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* memory node.
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* @sbq: Bitmap queue to initialize.
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* @depth: See sbitmap_init_node().
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* @shift: See sbitmap_init_node().
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* @flags: Allocation flags.
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* @node: Memory node to allocate on.
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*
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* Return: Zero on success or negative errno on failure.
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*/
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int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,
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int shift, gfp_t flags, int node);
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/**
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* sbitmap_queue_free() - Free memory used by a &struct sbitmap_queue.
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*
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* @sbq: Bitmap queue to free.
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*/
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static inline void sbitmap_queue_free(struct sbitmap_queue *sbq)
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{
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kfree(sbq->ws);
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sbitmap_free(&sbq->sb);
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}
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/**
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* sbitmap_queue_resize() - Resize a &struct sbitmap_queue.
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* @sbq: Bitmap queue to resize.
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* @depth: New number of bits to resize to.
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*
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* Like sbitmap_resize(), this doesn't reallocate anything. It has to do
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* some extra work on the &struct sbitmap_queue, so it's not safe to just
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* resize the underlying &struct sbitmap.
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*/
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void sbitmap_queue_resize(struct sbitmap_queue *sbq, unsigned int depth);
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/**
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* sbitmap_queue_clear() - Free an allocated bit and wake up waiters on a
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* &struct sbitmap_queue.
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* @sbq: Bitmap to free from.
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* @nr: Bit number to free.
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*/
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void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr);
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static inline int sbq_index_inc(int index)
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{
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return (index + 1) & (SBQ_WAIT_QUEUES - 1);
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}
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static inline void sbq_index_atomic_inc(atomic_t *index)
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{
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int old = atomic_read(index);
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int new = sbq_index_inc(old);
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atomic_cmpxchg(index, old, new);
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}
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/**
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* sbq_wait_ptr() - Get the next wait queue to use for a &struct
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* sbitmap_queue.
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* @sbq: Bitmap queue to wait on.
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* @wait_index: A counter per "user" of @sbq.
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*/
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static inline struct sbq_wait_state *sbq_wait_ptr(struct sbitmap_queue *sbq,
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atomic_t *wait_index)
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{
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struct sbq_wait_state *ws;
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ws = &sbq->ws[atomic_read(wait_index)];
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sbq_index_atomic_inc(wait_index);
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return ws;
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}
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/**
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* sbitmap_queue_wake_all() - Wake up everything waiting on a &struct
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* sbitmap_queue.
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* @sbq: Bitmap queue to wake up.
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*/
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void sbitmap_queue_wake_all(struct sbitmap_queue *sbq);
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#endif /* __LINUX_SCALE_BITMAP_H */
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