path: root/drivers/md/dm-cache-policy-mq.c

/*
 * Copyright (C) 2012 Red Hat. All rights reserved.
 *
 * This file is released under the GPL.
 */

#include "dm-cache-policy.h"
#include "dm.h"

#include <linux/hash.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>

#define DM_MSG_PREFIX "cache-policy-mq"

static struct kmem_cache *mq_entry_cache;

/*----------------------------------------------------------------*/

static unsigned next_power(unsigned n, unsigned min)
{
	return roundup_pow_of_two(max(n, min));
}

/*----------------------------------------------------------------*/

static unsigned long *alloc_bitset(unsigned nr_entries)
{
	size_t s = sizeof(unsigned long) * dm_div_up(nr_entries, BITS_PER_LONG);
	return vzalloc(s);
}

static void free_bitset(unsigned long *bits)
{
	vfree(bits);
}

/*----------------------------------------------------------------*/

/*
 * Large, sequential ios are probably better left on the origin device since
 * spindles tend to have good bandwidth.
 *
 * The io_tracker tries to spot when the io is in one of these sequential
 * modes.
 *
 * Two thresholds to switch between random and sequential io mode are defaulting
 * as follows and can be adjusted via the constructor and message interfaces.
 */
#define RANDOM_THRESHOLD_DEFAULT 4
#define SEQUENTIAL_THRESHOLD_DEFAULT 512

enum io_pattern {
	PATTERN_SEQUENTIAL,
	PATTERN_RANDOM
};

struct io_tracker {
	enum io_pattern pattern;

	unsigned nr_seq_samples;
	unsigned nr_rand_samples;
	unsigned thresholds[2];

	dm_oblock_t last_end_oblock;
};

static void iot_init(struct io_tracker *t,
		     int sequential_threshold, int random_threshold)
{
	t->pattern = PATTERN_RANDOM;
	t->nr_seq_samples = 0;
	t->nr_rand_samples = 0;
	t->last_end_oblock = 0;
	t->thresholds[PATTERN_RANDOM] = random_threshold;
	t->thresholds[PATTERN_SEQUENTIAL] = sequential_threshold;
}

static enum io_pattern iot_pattern(struct io_tracker *t)
{
	return t->pattern;
}

static void iot_update_stats(struct io_tracker *t, struct bio *bio)
{
	if (bio->bi_sector == from_oblock(t->last_end_oblock) + 1)
		t->nr_seq_samples++;
	else {
		/*
		 * Just one non-sequential IO is enough to reset the
		 * counters.
		 */
		if (t->nr_seq_samples) {
			t->nr_seq_samples = 0;
			t->nr_rand_samples = 0;
		}

		t->nr_rand_samples++;
	}

	t->last_end_oblock = to_oblock(bio->bi_sector + bio_sectors(bio) - 1);
}

static void iot_check_for_pattern_switch(struct io_tracker *t)
{
	switch (t->pattern) {
	case PATTERN_SEQUENTIAL:
		if (t->nr_rand_samples >= t->thresholds[PATTERN_RANDOM]) {
			t->pattern = PATTERN_RANDOM;
			t->nr_seq_samples = t->nr_rand_samples = 0;
		}
		break;

	case PATTERN_RANDOM:
		if (t->nr_seq_samples >= t->thresholds[PATTERN_SEQUENTIAL]) {
			t->pattern = PATTERN_SEQUENTIAL;
			t->nr_seq_samples = t->nr_rand_samples = 0;
		}
		break;
	}
}

static