diff options
Diffstat (limited to 'drivers/md/dm-cache-policy-smq.c')
| -rw-r--r-- | drivers/md/dm-cache-policy-smq.c | 1768 |
1 files changed, 1768 insertions, 0 deletions
diff --git a/drivers/md/dm-cache-policy-smq.c b/drivers/md/dm-cache-policy-smq.c new file mode 100644 index 000000000000..55a657f78f00 --- /dev/null +++ b/drivers/md/dm-cache-policy-smq.c @@ -0,0 +1,1768 @@ +/* + * Copyright (C) 2015 Red Hat. All rights reserved. + * + * This file is released under the GPL. + */ + +#include "dm-cache-policy.h" +#include "dm-cache-policy-internal.h" +#include "dm.h" + +#include <linux/hash.h> +#include <linux/jiffies.h> +#include <linux/module.h> +#include <linux/mutex.h> +#include <linux/vmalloc.h> +#include <linux/math64.h> + +#define DM_MSG_PREFIX "cache-policy-smq" + +/*----------------------------------------------------------------*/ + +/* + * Safe division functions that return zero on divide by zero. + */ +static unsigned safe_div(unsigned n, unsigned d) +{ + return d ? n / d : 0u; +} + +static unsigned safe_mod(unsigned n, unsigned d) +{ + return d ? n % d : 0u; +} + +/*----------------------------------------------------------------*/ + +struct entry { + unsigned hash_next:28; + unsigned prev:28; + unsigned next:28; + unsigned level:7; + bool dirty:1; + bool allocated:1; + bool sentinel:1; + + dm_oblock_t oblock; +}; + +/*----------------------------------------------------------------*/ + +#define INDEXER_NULL ((1u << 28u) - 1u) + +/* + * An entry_space manages a set of entries that we use for the queues. + * The clean and dirty queues share entries, so this object is separate + * from the queue itself. + */ +struct entry_space { + struct entry *begin; + struct entry *end; +}; + +static int space_init(struct entry_space *es, unsigned nr_entries) +{ + if (!nr_entries) { + es->begin = es->end = NULL; + return 0; + } + + es->begin = vzalloc(sizeof(struct entry) * nr_entries); + if (!es->begin) + return -ENOMEM; + + es->end = es->begin + nr_entries; + return 0; +} + +static void space_exit(struct entry_space *es) +{ + vfree(es->begin); +} + +static struct entry *__get_entry(struct entry_space *es, unsigned block) +{ + struct entry *e; + + e = es->begin + block; + BUG_ON(e >= es->end); + + return e; +} + +static unsigned to_index(struct entry_space *es, struct entry *e) +{ + BUG_ON(e < es->begin || e >= es->end); + return e - es->begin; +} + +static struct entry *to_entry(struct entry_space *es, unsigned block) +{ + if (block == INDEXER_NULL) + return NULL; + + return __get_entry(es, block); +} + +/*----------------------------------------------------------------*/ + +struct ilist { + unsigned nr_elts; /* excluding sentinel entries */ + unsigned head, tail; +}; + +static void l_init(struct ilist *l) +{ + l->nr_elts = 0; + l->head = l->tail = INDEXER_NULL; +} + +static struct entry *l_head(struct entry_space *es, struct ilist *l) +{ + return to_entry(es, l->head); +} + +static struct entry *l_tail(struct entry_space *es, struct ilist *l) +{ + return to_entry(es, l->tail); +} + +static struct entry *l_next(struct entry_space *es, struct entry *e) +{ + return to_entry(es, e->next); +} + +static struct entry *l_prev(struct entry_space *es, struct entry *e) +{ + return to_entry(es, e->prev); +} + +static bool l_empty(struct ilist *l) +{ + return l->head == INDEXER_NULL; +} + +static void l_add_head(struct entry_space *es, struct ilist *l, struct entry *e) +{ + struct entry *head = l_head(es, l); + + e->next = l->head; + e->prev = INDEXER_NULL; + + if (head) + head->prev = l->head = to_index(es, e); + else + l->head = l->tail = to_index(es, e); + + if (!e->sentinel) + l->nr_elts++; +} + +static void l_add_tail(struct entry_space *es, struct ilist *l, struct entry *e) +{ + struct entry *tail = l_tail(es, l); + + e->next = INDEXER_NULL; + e->prev = l->tail; + + if (tail) + tail->next = l->tail = to_index(es, e); + else + l->head = l->tail = to_index(es, e); + + if (!e->sentinel) + l->nr_elts++; +} + +static void l_add_before(struct entry_space *es, struct ilist *l, + struct entry *old, struct entry *e) +{ + struct entry *prev = l_prev(es, old); + + if (!prev) + l_add_head(es, l, e); + + else { + e->prev = old->prev; + e->next = to_index(es, old); + prev->next = old->prev = to_index(es, e); + + if (!e->sentinel) + l->nr_elts++; + } +} + +static void l_del(struct entry_space *es, struct ilist *l, struct entry *e) +{ + struct entry *prev = l_prev(es, e); + struct entry *next = l_next(es, e); + + if (prev) + prev->next = e->next; + else + l->head = e->next; + + if (next) + next->prev = e->prev; + else + l->tail = e->prev; + + if (!e->sentinel) + l->nr_elts--; +} + +static struct entry *l_pop_tail(struct entry_space *es, struct ilist *l) +{ + struct entry *e; + + for (e = l_tail(es, l); e; e = l_prev(es, e)) + if (!e->sentinel) { + l_del(es, l, e); + return e; + } + + return NULL; +} + +/*----------------------------------------------------------------*/ + +/* + * The stochastic-multi-queue is a set of lru lists stacked into levels. + * Entries are moved up levels when they are used, which loosely orders the + * most accessed entries in the top levels and least in the bottom. This + * structure is *much* better than a single lru list. + */ +#define MAX_LEVELS 64u + +struct queue { + struct entry_space *es; + + unsigned nr_elts; + unsigned nr_levels; + struct ilist qs[MAX_LEVELS]; + + /* + * We maintain a count of the number of entries we would like in each + * level. + */ + unsigned last_target_nr_elts; + unsigned nr_top_levels; + unsigned nr_in_top_levels; + unsigned target_count[MAX_LEVELS]; +}; + +static void q_init(struct queue *q, struct entry_space *es, unsigned nr_levels) +{ + unsigned i; + + q->es = es; + q->nr_elts = 0; + q->nr_levels = nr_levels; + + for (i = 0; i < q->nr_levels; i++) { + l_init(q->qs + i); + q->target_count[i] = 0u; + } + + q->last_target_nr_elts = 0u; + q->nr_top_levels = 0u; + q->nr_in_top_levels = 0u; +} + +static unsigned q_size(struct queue *q) +{ + return q->nr_elts; +} + +/* + * Insert an entry to the back of the given level. + */ +static void q_push(struct queue *q, struct entry *e) +{ + if (!e->sentinel) + q->nr_elts++; + + l_add_tail(q->es, q->qs + e->level, e); +} + +static void q_push_before(struct queue *q, struct entry *old, struct entry *e) +{ + if (!e->sentinel) + q->nr_elts++; + + l_add_before(q->es, q->qs + e->level, old, e); +} + +static void q_del(struct queue *q, struct entry *e) +{ + l_del(q->es, q->qs + e->level, e); + if (!e->sentinel) + q->nr_elts--; +} + +/* + * Return the oldest entry of the lowest populated level. + */ +static struct entry *q_peek(struct queue *q, unsigned max_level, bool can_cross_sentinel) +{ + unsigned level; + struct entry *e; + + max_level = min(max_level, q->nr_levels); + + for (level = 0; level < max_level; level++) + for (e = l_head(q->es, q->qs + level); e; e = l_next(q->es, e)) { + if (e->sentinel) { + if (can_cross_sentinel) + continue; + else + break; + } + + return e; + } + + return NULL; +} + +static struct entry *q_pop(struct queue *q) +{ + struct entry *e = q_peek(q, q->nr_levels, true); + + if (e) + q_del(q, e); + + return e; +} + +/* + * Pops an entry from a level that is not past a sentinel. + */ +static struct entry *q_pop_old(struct queue *q, unsigned max_level) +{ + struct entry *e = q_peek(q, max_level, false); + + if (e) + q_del(q, e); + + return e; +} + +/* + * This function assumes there is a non-sentinel entry to pop. It's only + * used by redistribute, so we know this is true. It also doesn't adjust + * the q->nr_elts count. + */ +static struct entry *__redist_pop_from(struct queue *q, unsigned level) +{ + struct entry *e; + + for (; level < q->nr_levels; level++) + for (e = l_head(q->es, q->qs + level); e; e = l_next(q->es, e)) + if (!e->sentinel) { + l_del(q->es, q->qs + e->level, e); + return e; + } + + return NULL; +} + +static void q_set_targets_subrange_(struct queue *q, unsigned nr_elts, unsigned lbegin, unsigned lend) +{ + unsigned level, nr_levels, entries_per_level, remainder; + + BUG_ON(lbegin > lend); + BUG_ON(lend > q->nr_levels); + nr_levels = lend - lbegin; + entries_per_level = safe_div(nr_elts, nr_levels); + remainder = safe_mod(nr_elts, nr_levels); + + for (level = lbegin; level < lend; level++) + q->target_count[level] = + (level < (lbegin + remainder)) ? entries_per_level + 1u : entries_per_level; +} + +/* + * Typically we have fewer elements in the top few levels which allows us + * to adjust the promote threshold nicely. + */ +static void q_set_targets(struct queue *q) +{ + if (q->last_target_nr_elts == q->nr_elts) + return; + + q->last_target_nr_elts = q->nr_elts; + + if (q->nr_top_levels > q->nr_levels) + q_set_targets_subrange_(q, q->nr_elts, 0, q->nr_levels); + + else { + q_set_targets_subrange_(q, q->nr_in_top_levels, + q->nr_levels - q->nr_top_levels, q->nr_levels); + + if (q->nr_in_top_levels < q->nr_elts) + q_set_targets_subrange_(q, q->nr_elts - q->nr_in_top_levels, + 0, q->nr_levels - q->nr_top_levels); + else + q_set_targets_subrange_(q, 0, 0, q->nr_levels - q->nr_top_levels); + } +} + +static void q_redistribute(struct queue *q) +{ + unsigned target, level; + struct ilist *l, *l_above; + struct entry *e; + + q_set_targets(q); + + for (level = 0u; level < q->nr_levels - 1u; level++) { + l = q->qs + level; + target = q->target_count[level]; + + /* + * Pull down some entries from the level above. + */ + while (l->nr_elts < target) { + e = __redist_pop_from(q, level + 1u); + if (!e) { + /* bug in nr_elts */ + break; + } + + e->level = level; + l_add_tail(q->es, l, e); + } + + /* + * Push some entries up. + */ + l_above = q->qs + level + 1u; + while (l->nr_elts > target) { + e = l_pop_tail(q->es, l); + + if (!e) + /* bug in nr_elts */ + break; + + e->level = level + 1u; + l_add_head(q->es, l_above, e); + } + } +} + +static void q_requeue_before(struct queue *q, struct entry *dest, struct entry *e, unsigned extra_levels) +{ + struct entry *de; + unsigned new_level; + + q_del(q, e); + + if (extra_levels && (e->level < q->nr_levels - 1u)) { + new_level = min(q->nr_levels - 1u, e->level + extra_levels); + for (de = l_head(q->es, q->qs + new_level); de; de = l_next(q->es, de)) { + if (de->sentinel) + continue; + + q_del(q, de); + de->level = e->level; + + if (dest) + q_push_before(q, dest, de); + else + q_push(q, de); + break; + } + + e->level = new_level; + } + + q_push(q, e); +} + +static void q_requeue(struct queue *q, struct entry *e, unsigned extra_levels) +{ + q_requeue_before(q, NULL, e, extra_levels); +} + +/*----------------------------------------------------------------*/ + +#define FP_SHIFT 8 +#define SIXTEENTH (1u << (FP_SHIFT - 4u)) +#define EIGHTH (1u << (FP_SHIFT - 3u)) + +struct stats { + unsigned hit_threshold; + unsigned hits; + unsigned misses; +}; + +enum performance { + Q_POOR, + Q_FAIR, + Q_WELL +}; + +static void stats_init(struct stats *s, unsigned nr_levels) +{ + s->hit_threshold = (nr_levels * 3u) / 4u; + s->hits = 0u; + s->misses = 0u; +} + +static void stats_reset(struct stats *s) +{ + s->hits = s->misses = 0u; +} + +static void stats_level_accessed(struct stats *s, unsigned level) +{ + if (level >= s->hit_threshold) + s->hits++; + else + s->misses++; +} + +static void stats_miss(struct stats *s) +{ + s->misses++; +} + +/* + * There are times when we don't have any confidence in the hotspot queue. + * Such as when a fresh cache is created and the blocks have been spread + * out across the levels, or if an io load changes. We detect this by + * seeing how often a lookup is in the top levels of the hotspot queue. + */ +static enum performance stats_assess(struct stats *s) +{ + unsigned confidence = safe_div(s->hits << FP_SHIFT, s->hits + s->misses); + + if (confidence < SIXTEENTH) + return Q_POOR; + + else if (confidence < EIGHTH) + return Q_FAIR; + + else + return Q_WELL; +} + +/*----------------------------------------------------------------*/ + +struct hash_table { + struct entry_space *es; + unsigned long long hash_bits; + unsigned *buckets; +}; + +/* + * All cache entries are stored in a chained hash table. To save space we + * use indexing again, and only store indexes to the next entry. + */ +static int h_init(struct hash_table *ht, struct entry_space *es, unsigned nr_entries) +{ + unsigned i, nr_buckets; + + ht->es = es; + nr_buckets = roundup_pow_of_two(max(nr_entries / 4u, 16u)); + ht->hash_bits = ffs(nr_buckets) - 1; + + ht->buckets = vmalloc(sizeof(*ht->buckets) * nr_buckets); + if (!ht->buckets) + return -ENOMEM; + + for (i = 0; i < nr_buckets; i++) + ht->buckets[i] = INDEXER_NULL; + + return 0; +} + +static void h_exit(struct hash_table *ht) +{ + vfree(ht->buckets); +} + +static struct entry *h_head(struct hash_table *ht, unsigned bucket) +{ + return to_entry(ht->es, ht->buckets[bucket]); +} + +static struct entry *h_next(struct hash_table *ht, struct entry *e) +{ + return to_entry(ht->es, e->hash_next); +} + +static void __h_insert(struct hash_table *ht, unsigned bucket, struct entry *e) +{ + e->hash_next = ht->buckets[bucket]; + ht->buckets[bucket] = to_index(ht->es, e); +} + +static void h_insert(struct hash_table *ht, struct entry *e) +{ + unsigned h = hash_64(from_oblock(e->oblock), ht->hash_bits); + __h_insert(ht, h, e); +} + +static struct entry *__h_lookup(struct hash_table *ht, unsigned h, dm_oblock_t oblock, + struct entry **prev) +{ + struct entry *e; + + *prev = NULL; + for (e = h_head(ht, h); e; e = h_next(ht, e)) { + if (e->oblock == oblock) + return e; + + *prev = e; + } + + return NULL; +} + +static void __h_unlink(struct hash_table *ht, unsigned h, + struct entry *e, struct entry *prev) +{ + if (prev) + prev->hash_next = e->hash_next; + else + ht->buckets[h] = e->hash_next; +} + +/* + * Also moves each entry to the front of the bucket. + */ +static struct entry *h_lookup(struct hash_table *ht, dm_oblock_t oblock) +{ + struct entry *e, *prev; + unsigned h = hash_64(from_oblock(oblock), ht->hash_bits); + + e = __h_lookup(ht, h, oblock, &prev); + if (e && prev) { + /* + * Move to the front because this entry is likely + * to be hit again. + */ + __h_unlink(ht, h, e, prev); + __h_insert(ht, h, e); + } + + return e; +} + +static void h_remove(struct hash_table *ht, struct entry *e) +{ + unsigned h = hash_64(from_oblock(e->oblock), ht->hash_bits); + struct entry *prev; + + /* + * The down side of using a singly linked list is we have to + * iterate the bucket to remove an item. + */ + e = __h_lookup(ht, h, e->oblock, &prev); + if (e) + __h_unlink(ht, h, e, prev); +} + +/*----------------------------------------------------------------*/ + +struct entry_alloc { + struct entry_space *es; + unsigned begin; + + unsigned nr_allocated; + struct ilist free; +}; + +static void init_allocator(struct entry_alloc *ea, struct entry_space *es, + unsigned begin, unsigned end) +{ + unsigned i; + + ea->es = es; + ea->nr_allocated = 0u; + ea->begin = begin; + + l_init(&ea->free); + for (i = begin; i != end; i++) + l_add_tail(ea->es, &ea->free, __get_entry(ea->es, i)); +} + +static void init_entry(struct entry *e) +{ + /* + * We can't memset because that would clear the hotspot and + * sentinel bits which remain constant. + */ + e->hash_next = INDEXER_NULL; + e->next = INDEXER_NULL; + e->prev = INDEXER_NULL; + e->level = 0u; + e->allocated = true; +} + +static struct entry *alloc_entry(struct entry_alloc *ea) +{ + struct entry *e; + + if (l_empty(&ea->free)) + return NULL; + + e = l_pop_tail(ea->es, &ea->free); + init_entry(e); + ea->nr_allocated++; + + return e; +} + +/* + * This assumes the cblock hasn't already been allocated. + */ +static struct entry *alloc_particular_entry(struct entry_alloc *ea, unsigned i) +{ + struct entry *e = __get_entry(ea->es, ea->begin + i); + + BUG_ON(e->allocated); + + l_del(ea->es, &ea->free, e); + init_entry(e); + ea->nr_allocated++; + + return e; +} + +static void free_entry(struct entry_alloc *ea, struct entry *e) +{ + BUG_ON(!ea->nr_allocated); + BUG_ON(!e->allocated); + + ea->nr_allocated--; + e->allocated = false; + l_add_tail(ea->es, &ea->free, e); +} + +static bool allocator_empty(struct entry_alloc *ea) +{ + return l_empty(&ea->free); +} + +static unsigned get_index(struct entry_alloc *ea, struct entry *e) +{ + return to_index(ea->es, e) - ea->begin; +} + +static struct entry *get_entry(struct entry_alloc *ea, unsigned index) +{ + return __get_entry(ea->es, ea->begin + index); +} + +/*----------------------------------------------------------------*/ + +#define NR_HOTSPOT_LEVELS 64u +#define NR_CACHE_LEVELS 64u + +#define WRITEBACK_PERIOD (10 * HZ) +#define DEMOTE_PERIOD (60 * HZ) + +#define HOTSPOT_UPDATE_PERIOD (HZ) +#define CACHE_UPDATE_PERIOD (10u * HZ) + +struct smq_policy { + struct dm_cache_policy policy; + + /* protects everything */ + struct mutex lock; + dm_cblock_t cache_size; + sector_t cache_block_size; + + sector_t hotspot_block_size; + unsigned nr_hotspot_blocks; + unsigned cache_blocks_per_hotspot_block; + unsigned hotspot_level_jump; + + struct entry_space es; + struct entry_alloc writeback_sentinel_alloc; + struct entry_alloc demote_sentinel_alloc; + struct entry_alloc hotspot_alloc; + struct entry_alloc cache_alloc; + + unsigned long *hotspot_hit_bits; + unsigned long *cache_hit_bits; + + /* + * We maintain three queues of entries. The cache proper, + * consisting of a clean and dirty queue, containing the currently + * active mappings. The hotspot queue uses a larger block size to + * track blocks that are being hit frequently and potential + * candidates for promotion to the cache. + */ + struct queue hotspot; + struct queue clean; + struct queue dirty; + + struct stats hotspot_stats; + struct stats cache_stats; + + /* + * Keeps track of time, incremented by the core. We use this to + * avoid attributing multiple hits within the same tick. + * + * Access to tick_protected should be done with the spin lock held. + * It's copied to tick at the start of the map function (within the + * mutex). + */ + spinlock_t tick_lock; + unsigned tick_protected; + unsigned tick; + + /* + * The hash tables allows us to quickly find an entry by origin + * block. + */ + struct hash_table table; + struct hash_table hotspot_table; + + bool current_writeback_sentinels; + unsigned long next_writeback_period; + + bool current_demote_sentinels; + unsigned long next_demote_period; + + unsigned write_promote_level; + unsigned read_promote_level; + + unsigned long next_hotspot_period; + unsigned long next_cache_period; +}; + +/*----------------------------------------------------------------*/ + +static struct entry *get_sentinel(struct entry_alloc *ea, unsigned level, bool which) +{ + return get_entry(ea, which ? level : NR_CACHE_LEVELS + level); +} + +static struct entry *writeback_sentinel(struct smq_policy *mq, unsigned level) +{ + return get_sentinel(&mq->writeback_sentinel_alloc, level, mq->current_writeback_sentinels); +} + +static struct entry *demote_sentinel(struct smq_policy *mq, unsigned level) +{ + return get_sentinel(&mq->demote_sentinel_alloc, level, mq->current_demote_sentinels); +} + +static void __update_writeback_sentinels(struct smq_policy *mq) +{ + unsigned level; + struct queue *q = &mq->dirty; + struct entry *sentinel; + + for (level = 0; level < q->nr_levels; level++) { + sentinel = writeback_sentinel(mq, level); + q_del(q, sentinel); + q_push(q, sentinel); + } +} + +static void __update_demote_sentinels(struct smq_policy *mq) +{ + unsigned level; + struct queue *q = &mq->clean; + struct entry *sentinel; + + for (level = 0; level < q->nr_levels; level++) { + sentinel = demote_sentinel(mq, level); + q_del(q, sentinel); + q_push(q, sentinel); + } +} + +static void update_sentinels(struct smq_policy *mq) +{ + if (time_after(jiffies, mq->next_writeback_period)) { + __update_writeback_sentinels(mq); + mq->next_writeback_period = jiffies + WRITEBACK_PERIOD; + mq->current_writeback_sentinels = !mq->current_writeback_sentinels; + } + + if (time_after(jiffies, mq->next_demote_period)) { + __update_demote_sentinels(mq); + mq->next_demote_period = jiffies + DEMOTE_PERIOD; + mq->current_demote_sentinels = !mq->current_demote_sentinels; + } +} + +static void __sentinels_init(struct smq_policy *mq) +{ + unsigned level; + struct entry *sentinel; + + for (level = 0; level < NR_CACHE_LEVELS; level++) { + sentinel = writeback_sentinel(mq, level); + sentinel->level = level; + q_push(&mq->dirty, sentinel); + + sentinel = demote_sentinel(mq, level); + sentinel->level = level; + q_push(&mq->clean, sentinel); + } +} + +static void sentinels_init(struct smq_policy *mq) +{ + mq->next_writeback_period = jiffies + WRITEBACK_PERIOD; + mq->next_demote_period = jiffies + DEMOTE_PERIOD; + + mq->current_writeback_sentinels = false; + mq->current_demote_sentinels = false; + __sentinels_init(mq); + + mq->current_writeback_sentinels = !mq->current_writeback_sentinels; + mq->current_demote_sentinels = !mq->current_demote_sentinels; + __sentinels_init(mq); +} + +/*----------------------------------------------------------------*/ + +/* + * These methods tie together the dirty queue, clean queue and hash table. + */ +static void push_new(struct smq_policy *mq, struct entry *e) +{ + struct queue *q = e->dirty ? &mq->dirty : &mq->clean; + h_insert(&mq->table, e); + q_push(q, e); +} + +static void push(struct smq_policy *mq, struct entry *e) +{ + struct entry *sentinel; + + h_insert(&mq->table, e); + + /* + * Punch this into the queue just in front of the sentinel, to + * ensure it's cleaned straight away. + */ + if (e->dirty) { + sentinel = writeback_sentinel(mq, e->level); + q_push_before(&mq->dirty, sentinel, e); + } else { + sentinel = demote_sentinel(mq, e->level); + q_push_before(&mq->clean, sentinel, e); + } +} + +/* + * Removes an entry from cache. Removes from the hash table. + */ +static void __del(struct smq_policy *mq, struct queue *q, struct entry *e) +{ + q_del(q, e); + h_remove(&mq->table, e); +} + +static void del(struct smq_policy *mq, struct entry *e) +{ + __del(mq, e->dirty ? &mq->dirty : &mq->clean, e); +} + +static struct entry *pop_old(struct smq_policy *mq, struct queue *q, unsigned max_level) +{ + struct entry *e = q_pop_old(q, max_level); + if (e) + h_remove(&mq->table, e); + return e; +} + +static dm_cblock_t infer_cblock(struct smq_policy *mq, struct entry *e) +{ + return to_cblock(get_index(&mq->cache_alloc, e)); +} + +static void requeue(struct smq_policy *mq, struct entry *e) +{ + struct entry *sentinel; + + if (!test_and_set_bit(from_cblock(infer_cblock(mq, e)), mq->cache_hit_bits)) { + if (e->dirty) { + sentinel = writeback_sentinel(mq, e->level); + q_requeue_before(&mq->dirty, sentinel, e, 1u); + } else { + sentinel = demote_sentinel(mq, e->level); + q_requeue_before(&mq->clean, sentinel, e, 1u); + } + } +} + +static unsigned default_promote_level(struct smq_policy *mq) +{ + /* + * The promote level depends on the current performance of the + * cache. + * + * If the cache is performing badly, then we can't afford + * to promote much without causing performance to drop below that + * of the origin device. + * + * If the cache is performing well, then we don't need to promote + * much. If it isn't broken, don't fix it. + * + * If the cache is middling then we promote more. + * + * This scheme reminds me of a graph of entropy vs probability of a + * binary variable. + */ + static unsigned table[] = {1, 1, 1, 2, 4, 6, 7, 8, 7, 6, 4, 4, 3, 3, 2, 2, 1}; + + unsigned hits = mq->cache_stats.hits; + unsigned misses = mq->cache_stats.misses; + unsigned index = safe_div(hits << 4u, hits + misses); + return table[index]; +} + +static void update_promote_levels(struct smq_policy *mq) +{ + /* + * If there are unused cache entries then we want to be really + * eager to promote. + */ + unsigned threshold_level = allocator_empty(&mq->cache_alloc) ? + default_promote_level(mq) : (NR_HOTSPOT_LEVELS / 2u); + + /* + * If the hotspot queue is performing badly then we have little + * confidence that we know which blocks to promote. So we cut down + * the amount of promotions. + */ + switch (stats_assess(&mq->hotspot_stats)) { + case Q_POOR: + threshold_level /= 4u; + break; + + case Q_FAIR: + threshold_level /= 2u; + break; + + case Q_WELL: + break; + } + + mq->read_promote_level = NR_HOTSPOT_LEVELS - threshold_level; + mq->write_promote_level = (NR_HOTSPOT_LEVELS - threshold_level) + 2u; +} + +/* + * If the hotspot queue is performing badly, then we try and move entries + * around more quickly. + */ +static void update_level_jump(struct smq_policy *mq) +{ + switch (stats_assess(&mq->hotspot_stats)) { + case Q_POOR: + mq->hotspot_level_jump = 4u; + break; + + case Q_FAIR: + mq->hotspot_level_jump = 2u; + break; + + case Q_WELL: + mq->hotspot_level_jump = 1u; + break; + } +} + +static void end_hotspot_period(struct smq_policy *mq) +{ + clear_bitset(mq->hotspot_hit_bits, mq->nr_hotspot_blocks); + update_promote_levels(mq); + + if (time_after(jiffies, mq->next_hotspot_period)) { + update_level_jump(mq); + q_redistribute(&mq->hotspot); + stats_reset(&mq->hotspot_stats); + mq->next_hotspot_period = jiffies + HOTSPOT_UPDATE_PERIOD; + } +} + +static void end_cache_period(struct smq_policy *mq) +{ + if (time_after(jiffies, mq->next_cache_period)) { + clear_bitset(mq->cache_hit_bits, from_cblock(mq->cache_size)); + + q_redistribute(&mq->dirty); + q_redistribute(&mq->clean); + stats_reset(&mq->cache_stats); + + mq->next_cache_period = jiffies + CACHE_UPDATE_PERIOD; + } +} + +static int demote_cblock(struct smq_policy *mq, + struct policy_locker *locker, + dm_oblock_t *oblock) +{ + struct entry *demoted = q_peek(&mq->clean, mq->clean.nr_levels, false); + if (!demoted) + /* + * We could get a block from mq->dirty, but that + * would add extra latency to the triggering bio as it + * waits for the writeback. Better to not promote this + * time and hope there's a clean block next time this block + * is hit. + */ + return -ENOSPC; + + if (locker->fn(locker, demoted->oblock)) + /* + * We couldn't lock this block. + */ + return -EBUSY; + + del(mq, demoted); + *oblock = demoted->oblock; + free_entry(&mq->cache_alloc, demoted); + + return 0; +} + +enum promote_result { + PROMOTE_NOT, + PROMOTE_TEMPORARY, + PROMOTE_PERMANENT +}; + +/* + * Converts a boolean into a promote result. + */ +static enum promote_result maybe_promote(bool promote) +{ + return promote ? PROMOTE_PERMANENT : PROMOTE_NOT; +} + +static enum promote_result should_promote(struct smq_policy *mq, struct entry *hs_e, struct bio *bio, + bool fast_promote) +{ + if (bio_data_dir(bio) == WRITE) { + if (!allocator_empty(&mq->cache_alloc) && fast_promote) + return PROMOTE_TEMPORARY; + + else + return maybe_promote(hs_e->level >= mq->write_promote_level); + } else + return maybe_promote(hs_e->level >= mq->read_promote_level); +} + +static void insert_in_cache(struct smq_policy *mq, dm_oblock_t oblock, + struct policy_locker *locker, + struct policy_result *result, enum promote_result pr) +{ + int r; + struct entry *e; + + if (allocator_empty(&mq->cache_alloc)) { + result->op = POLICY_REPLACE; + r = demote_cblock(mq, locker, &result->old_oblock); + if (r) { + result->op = POLICY_MISS; + return; + } + + } else + result->op = POLICY_NEW; + + e = alloc_entry(&mq->cache_alloc); + BUG_ON(!e); + e->oblock = oblock; + + if (pr == PROMOTE_TEMPORARY) + push(mq, e); + else + push_new(mq, e); + + result->cblock = infer_cblock(mq, e); +} + +static dm_oblock_t to_hblock(struct smq_policy *mq, dm_oblock_t b) +{ + sector_t r = from_oblock(b); + (void) sector_div(r, mq->cache_blocks_per_hotspot_block); + return to_oblock(r); +} + +static struct entry *update_hotspot_queue(struct smq_policy *mq, dm_oblock_t b, struct bio *bio) +{ + unsigned hi; + dm_oblock_t hb = to_hblock(mq, b); + struct entry *e = h_lookup(&mq->hotspot_table, hb); + + if (e) { + stats_level_accessed(&mq->hotspot_stats, e->level); + + hi = get_index(&mq->hotspot_alloc, e); + q_requeue(&mq->hotspot, e, + test_and_set_bit(hi, mq->hotspot_hit_bits) ? + 0u : mq->hotspot_level_jump); + + } else { + stats_miss(&mq->hotspot_stats); + + e = alloc_entry(&mq->hotspot_alloc); + if (!e) { + e = q_pop(&mq->hotspot); + if (e) { + h_remove(&mq->hotspot_table, e); + hi = get_index(&mq->hotspot_alloc, e); + clear_bit(hi, mq->hotspot_hit_bits); + } + + } + + if (e) { + e->oblock = hb; + q_push(&mq->hotspot, e); + h_insert(&mq->hotspot_table, e); + } + } + + return e; +} + +/* + * Looks the oblock up in the hash table, then decides whether to put in + * pre_cache, or cache etc. + */ +static int map(struct smq_policy *mq, struct bio *bio, dm_oblock_t oblock, + bool can_migrate, bool fast_promote, + struct policy_locker *locker, struct policy_result *result) +{ + struct entry *e, *hs_e; + enum promote_result pr; + + hs_e = update_hotspot_queue(mq, oblock, bio); + + e = h_lookup(&mq->table, oblock); + if (e) { + stats_level_accessed(&mq->cache_stats, e->level); + + requeue(mq, e); + result->op = POLICY_HIT; + result->cblock = infer_cblock(mq, e); + + } else { + stats_miss(&mq->cache_stats); + + pr = should_promote(mq, hs_e, bio, fast_promote); + if (pr == PROMOTE_NOT) + result->op = POLICY_MISS; + + else { + if (!can_migrate) { + result->op = POLICY_MISS; + return -EWOULDBLOCK; + } + + insert_in_cache(mq, oblock, locker, result, pr); + } + } + + return 0; +} + +/*----------------------------------------------------------------*/ + +/* + * Public interface, via the policy struct. See dm-cache-policy.h for a + * description of these. + */ + +static struct smq_policy *to_smq_policy(struct dm_cache_policy *p) +{ + return container_of(p, struct smq_policy, policy); +} + +static void smq_destroy(struct dm_cache_policy *p) +{ + struct smq_policy *mq = to_smq_policy(p); + + h_exit(&mq->hotspot_table); + h_exit(&mq->table); + free_bitset(mq->hotspot_hit_bits); + free_bitset(mq->cache_hit_bits); + space_exit(&mq->es); + kfree(mq); +} + +static void copy_tick(struct smq_policy *mq) +{ + unsigned long flags, tick; + + spin_lock_irqsave(&mq->tick_lock, flags); + tick = mq->tick_protected; + if (tick != mq->tick) { + update_sentinels(mq); + end_hotspot_period(mq); + end_cache_period(mq); + mq->tick = tick; + } + spin_unlock_irqrestore(&mq->tick_lock, flags); +} + +static bool maybe_lock(struct smq_policy *mq, bool can_block) +{ + if (can_block) { + mutex_lock(&mq->lock); + return true; + } else + return mutex_trylock(&mq->lock); +} + +static int smq_map(struct dm_cache_policy *p, dm_oblock_t oblock, + bool can_block, bool can_migrate, bool fast_promote, + struct bio *bio, struct policy_locker *locker, + struct policy_result *result) +{ + int r; + struct smq_policy *mq = to_smq_policy(p); + + result->op = POLICY_MISS; + + if (!maybe_lock(mq, can_block)) + return -EWOULDBLOCK; + + copy_tick(mq); + r = map(mq, bio, oblock, can_migrate, fast_promote, locker, result); + mutex_unlock(&mq->lock); + + return r; +} + +static int smq_lookup(struct dm_cache_policy *p, dm_oblock_t oblock, dm_cblock_t *cblock) +{ + int r; + struct smq_policy *mq = to_smq_policy(p); + struct entry *e; + + if (!mutex_trylock(&mq->lock)) + return -EWOULDBLOCK; + + e = h_lookup(&mq->table, oblock); + if (e) { + *cblock = infer_cblock(mq, e); + r = 0; + } else + r = -ENOENT; + + mutex_unlock(&mq->lock); + + return r; +} + +static void __smq_set_clear_dirty(struct smq_policy *mq, dm_oblock_t oblock, bool set) +{ + struct entry *e; + + e = h_lookup(&mq->table, oblock); + BUG_ON(!e); + + del(mq, e); + e->dirty = set; + push(mq, e); +} + +static void smq_set_dirty(struct dm_cache_policy *p, dm_oblock_t oblock) +{ + struct smq_policy *mq = to_smq_policy(p); + + mutex_lock(&mq->lock); + __smq_set_clear_dirty(mq, oblock, true); + mutex_unlock(&mq->lock); +} + +static void smq_clear_dirty(struct dm_cache_policy *p, dm_oblock_t oblock) +{ + struct smq_policy *mq = to_smq_policy(p); + + mutex_lock(&mq->lock); + __smq_set_clear_dirty(mq, oblock, false); + mutex_unlock(&mq->lock); +} + +static int smq_load_mapping(struct dm_cache_policy *p, + dm_oblock_t oblock, dm_cblock_t cblock, + uint32_t hint, bool hint_valid) +{ + struct smq_policy *mq = to_smq_policy(p); + struct entry *e; + + e = alloc_particular_entry(&mq->cache_alloc, from_cblock(cblock)); + e->oblock = oblock; + e->dirty = false; /* this gets corrected in a minute */ + e->level = hint_valid ? min(hint, NR_CACHE_LEVELS - 1) : 1; + push(mq, e); + + return 0; +} + +static int smq_save_hints(struct smq_policy *mq, struct queue *q, + policy_walk_fn fn, void *context) +{ + int r; + unsigned level; + struct entry *e; + + for (level = 0; level < q->nr_levels; level++) + for (e = l_head(q->es, q->qs + level); e; e = l_next(q->es, e)) { + if (!e->sentinel) { + r = fn(context, infer_cblock(mq, e), + e->oblock, e->level); + if (r) + return r; + } + } + + return 0; +} + +static int smq_walk_mappings(struct dm_cache_policy *p, policy_walk_fn fn, + void *context) +{ + struct smq_policy *mq = to_smq_policy(p); + int r = 0; + + mutex_lock(&mq->lock); + + r = smq_save_hints(mq, &mq->clean, fn, context); + if (!r) + r = smq_save_hints(mq, &mq->dirty, fn, context); + + mutex_unlock(&mq->lock); + + return r; +} + +static void __remove_mapping(struct smq_policy *mq, dm_oblock_t oblock) +{ + struct entry *e; + + e = h_lookup(&mq->table, oblock); + BUG_ON(!e); + + del(mq, e); + free_entry(&mq->cache_alloc, e); +} + +static void smq_remove_mapping(struct dm_cache_policy *p, dm_oblock_t oblock) +{ + struct smq_policy *mq = to_smq_policy(p); + + mutex_lock(&mq->lock); + __remove_mapping(mq, oblock); + mutex_unlock(&mq->lock); +} + +static int __remove_cblock(struct smq_policy *mq, dm_cblock_t cblock) +{ + struct entry *e = get_entry(&mq->cache_alloc, from_cblock(cblock)); + + if (!e || !e->allocated) + return -ENODATA; + + del(mq, e); + free_entry(&mq->cache_alloc, e); + + return 0; +} + +static int smq_remove_cblock(struct dm_cache_policy *p, dm_cblock_t cblock) +{ + int r; + struct smq_policy *mq = to_smq_policy(p); + + mutex_lock(&mq->lock); + r = __remove_cblock(mq, cblock); + mutex_unlock(&mq->lock); + + return r; +} + + +#define CLEAN_TARGET_CRITICAL 5u /* percent */ + +static bool clean_target_met(struct smq_policy *mq, bool critical) +{ + if (critical) { + /* + * Cache entries may not be populated. So we're cannot rely on the + * size of the clean queue. + */ + unsigned nr_clean = from_cblock(mq->cache_size) - q_size(&mq->dirty); + unsigned target = from_cblock(mq->cache_size) * CLEAN_TARGET_CRITICAL / 100u; + + return nr_clean >= target; + } else + return !q_size(&mq->dirty); +} + +static int __smq_writeback_work(struct smq_policy *mq, dm_oblock_t *oblock, + dm_cblock_t *cblock, bool critical_only) +{ + struct entry *e = NULL; + bool target_met = clean_target_met(mq, critical_only); + + if (critical_only) + /* + * Always try and keep the bottom level clean. + */ + e = pop_old(mq, &mq->dirty, target_met ? 1u : mq->dirty.nr_levels); + + else + e = pop_old(mq, &mq->dirty, mq->dirty.nr_levels); + + if (!e) + return -ENODATA; + + *oblock = e->oblock; + *cblock = infer_cblock(mq, e); + e->dirty = false; + push_new(mq, e); + + return 0; +} + +static int smq_writeback_work(struct dm_cache_policy *p, dm_oblock_t *oblock, + dm_cblock_t *cblock, bool critical_only) +{ + int r; + struct smq_policy *mq = to_smq_policy(p); + + mutex_lock(&mq->lock); + r = __smq_writeback_work(mq, oblock, cblock, critical_only); + mutex_unlock(&mq->lock); + + return r; +} + +static void __force_mapping(struct smq_policy *mq, + dm_oblock_t current_oblock, dm_oblock_t new_oblock) +{ + struct entry *e = h_lookup(&mq->table, current_oblock); + + if (e) { + del(mq, e); + e->oblock = new_oblock; + e->dirty = true; + push(mq, e); + } +} + +static void smq_force_mapping(struct dm_cache_policy *p, + dm_oblock_t current_oblock, dm_oblock_t new_oblock) +{ + struct smq_policy *mq = to_smq_policy(p); + + mutex_lock(&mq->lock); + __force_mapping(mq, current_oblock, new_oblock); + mutex_unlock(&mq->lock); +} + +static dm_cblock_t smq_residency(struct dm_cache_policy *p) +{ + dm_cblock_t r; + struct smq_policy *mq = to_smq_policy(p); + + mutex_lock(&mq->lock); + r = to_cblock(mq->cache_alloc.nr_allocated); + mutex_unlock(&mq->lock); + + return r; +} + +static void smq_tick(struct dm_cache_policy *p) +{ + struct smq_policy *mq = to_smq_policy(p); + unsigned long flags; + + spin_lock_irqsave(&mq->tick_lock, flags); + mq->tick_protected++; + spin_unlock_irqrestore(&mq->tick_lock, flags); +} + +/* Init the policy plugin interface function pointers. */ +static void init_policy_functions(struct smq_policy *mq) +{ + mq->policy.destroy = smq_destroy; + mq->policy.map = smq_map; + mq->policy.lookup = smq_lookup; + mq->policy.set_dirty = smq_set_dirty; + mq->policy.clear_dirty = smq_clear_dirty; + mq->policy.load_mapping = smq_load_mapping; + mq->policy.walk_mappings = smq_walk_mappings; + mq->policy.remove_mapping = smq_remove_mapping; + mq->policy.remove_cblock = smq_remove_cblock; + mq->policy.writeback_work = smq_writeback_work; + mq->policy.force_mapping = smq_force_mapping; + mq->policy.residency = smq_residency; + mq->policy.tick = smq_tick; +} + +static bool too_many_hotspot_blocks(sector_t origin_size, + sector_t hotspot_block_size, + unsigned nr_hotspot_blocks) +{ + return (hotspot_block_size * nr_hotspot_blocks) > origin_size; +} + +static void calc_hotspot_params(sector_t origin_size, + sector_t cache_block_size, + unsigned nr_cache_blocks, + sector_t *hotspot_block_size, + unsigned *nr_hotspot_blocks) +{ + *hotspot_block_size = cache_block_size * 16u; + *nr_hotspot_blocks = max(nr_cache_blocks / 4u, 1024u); + + while ((*hotspot_block_size > cache_block_size) && + too_many_hotspot_blocks(origin_size, *hotspot_block_size, *nr_hotspot_blocks)) + *hotspot_block_size /= 2u; +} + +static struct dm_cache_policy *smq_create(dm_cblock_t cache_size, + sector_t origin_size, + sector_t cache_block_size) +{ + unsigned i; + unsigned nr_sentinels_per_queue = 2u * NR_CACHE_LEVELS; + unsigned total_sentinels = 2u * nr_sentinels_per_queue; + struct smq_policy *mq = kzalloc(sizeof(*mq), GFP_KERNEL); + + if (!mq) + return NULL; + + init_policy_functions(mq); + mq->cache_size = cache_size; + mq->cache_block_size = cache_block_size; + + calc_hotspot_params(origin_size, cache_block_size, from_cblock(cache_size), + &mq->hotspot_block_size, &mq->nr_hotspot_blocks); + + mq->cache_blocks_per_hotspot_block = div64_u64(mq->hotspot_block_size, mq->cache_block_size); + mq->hotspot_level_jump = 1u; + if (space_init(&mq->es, total_sentinels + mq->nr_hotspot_blocks + from_cblock(cache_size))) { + DMERR("couldn't initialize entry space"); + goto bad_pool_init; + } + + init_allocator(&mq->writeback_sentinel_alloc, &mq->es, 0, nr_sentinels_per_queue); + for (i = 0; i < nr_sentinels_per_queue; i++) + get_entry(&mq->writeback_sentinel_alloc, i)->sentinel = true; + + init_allocator(&mq->demote_sentinel_alloc, &mq->es, nr_sentinels_per_queue, total_sentinels); + for (i = 0; i < nr_sentinels_per_queue; i++) + get_entry(&mq->demote_sentinel_alloc, i)->sentinel = true; + + init_allocator(&mq->hotspot_alloc, &mq->es, total_sentinels, + total_sentinels + mq->nr_hotspot_blocks); + + init_allocator(&mq->cache_alloc, &mq->es, + total_sentinels + mq->nr_hotspot_blocks, + total_sentinels + mq->nr_hotspot_blocks + from_cblock(cache_size)); + + mq->hotspot_hit_bits = alloc_bitset(mq->nr_hotspot_blocks); + if (!mq->hotspot_hit_bits) { + DMERR("couldn't allocate hotspot hit bitset"); + goto bad_hotspot_hit_bits; + } + clear_bitset(mq->hotspot_hit_bits, mq->nr_hotspot_blocks); + + if (from_cblock(cache_size)) { + mq->cache_hit_bits = alloc_bitset(from_cblock(cache_size)); + if (!mq->cache_hit_bits && mq->cache_hit_bits) { + DMERR("couldn't allocate cache hit bitset"); + goto bad_cache_hit_bits; + } + clear_bitset(mq->cache_hit_bits, from_cblock(mq->cache_size)); + } else + mq->cache_hit_bits = NULL; + + mq->tick_protected = 0; + mq->tick = 0; + mutex_init(&mq->lock); + spin_lock_init(&mq->tick_lock); + + q_init(&mq->hotspot, &mq->es, NR_HOTSPOT_LEVELS); + mq->hotspot.nr_top_levels = 8; + mq->hotspot.nr_in_top_levels = min(mq->nr_hotspot_blocks / NR_HOTSPOT_LEVELS, + from_cblock(mq->cache_size) / mq->cache_blocks_per_hotspot_block); + + q_init(&mq->clean, &mq->es, NR_CACHE_LEVELS); + q_init(&mq->dirty, &mq->es, NR_CACHE_LEVELS); + + stats_init(&mq->hotspot_stats, NR_HOTSPOT_LEVELS); + stats_init(&mq->cache_stats, NR_CACHE_LEVELS); + + if (h_init(&mq->table, &mq->es, from_cblock(cache_size))) + goto bad_alloc_table; + + if (h_init(&mq->hotspot_table, &mq->es, mq->nr_hotspot_blocks)) + goto bad_alloc_hotspot_table; + + sentinels_init(mq); + mq->write_promote_level = mq->read_promote_level = NR_HOTSPOT_LEVELS; + + mq->next_hotspot_period = jiffies; + mq->next_cache_period = jiffies; + + return &mq->policy; + +bad_alloc_hotspot_table: + h_exit(&mq->table); +bad_alloc_table: + free_bitset(mq->cache_hit_bits); +bad_cache_hit_bits: + free_bitset(mq->hotspot_hit_bits); +bad_hotspot_hit_bits: + space_exit(&mq->es); +bad_pool_init: + kfree(mq); + + return NULL; +} + +/*----------------------------------------------------------------*/ + +static struct dm_cache_policy_type smq_policy_type = { + .name = "smq", + .version = {1, 0, 0}, + .hint_size = 4, + .owner = THIS_MODULE, + .create = smq_create +}; + +static int __init smq_init(void) +{ + int r; + + r = dm_cache_policy_register(&smq_policy_type); + if (r) { + DMERR("register failed %d", r); + return -ENOMEM; + } + + return 0; +} + +static void __exit smq_exit(void) +{ + dm_cache_policy_unregister(&smq_policy_type); +} + +module_init(smq_init); +module_exit(smq_exit); + +MODULE_AUTHOR("Joe Thornber <dm-devel@redhat.com>"); +MODULE_LICENSE("GPL"); +MODULE_DESCRIPTION("smq cache policy"); |