dm cache: make the 'mq' policy an alias for 'smq'
authorJoe Thornber <ejt@redhat.com>
Wed, 10 Feb 2016 10:18:10 +0000 (10:18 +0000)
committerMike Snitzer <snitzer@redhat.com>
Thu, 10 Mar 2016 22:12:08 +0000 (17:12 -0500)
smq seems to be performing better than the old mq policy in all
situations, as well as using a quarter of the memory.

Make 'mq' an alias for 'smq' when choosing a cache policy.  The tunables
that were present for the old mq are faked, and have no effect.  mq
should be considered deprecated now.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Documentation/device-mapper/cache-policies.txt
drivers/md/Kconfig
drivers/md/Makefile
drivers/md/dm-cache-policy-mq.c [deleted file]
drivers/md/dm-cache-policy-smq.c

index d9246a32e673f273c03bdd2a0da9c44373c11891..e5062ad1871798339c70ab0b241218c0c4ee3070 100644 (file)
@@ -28,51 +28,16 @@ Overview of supplied cache replacement policies
 multiqueue (mq)
 ---------------
 
-This policy has been deprecated in favor of the smq policy (see below).
+This policy is now an alias for smq (see below).
 
-The multiqueue policy has three sets of 16 queues: one set for entries
-waiting for the cache and another two for those in the cache (a set for
-clean entries and a set for dirty entries).
+The following tunables are accepted, but have no effect:
 
-Cache entries in the queues are aged based on logical time. Entry into
-the cache is based on variable thresholds and queue selection is based
-on hit count on entry. The policy aims to take different cache miss
-costs into account and to adjust to varying load patterns automatically.
-
-Message and constructor argument pairs are:
        'sequential_threshold <#nr_sequential_ios>'
        'random_threshold <#nr_random_ios>'
        'read_promote_adjustment <value>'
        'write_promote_adjustment <value>'
        'discard_promote_adjustment <value>'
 
-The sequential threshold indicates the number of contiguous I/Os
-required before a stream is treated as sequential.  Once a stream is
-considered sequential it will bypass the cache.  The random threshold
-is the number of intervening non-contiguous I/Os that must be seen
-before the stream is treated as random again.
-
-The sequential and random thresholds default to 512 and 4 respectively.
-
-Large, sequential I/Os are probably better left on the origin device
-since spindles tend to have good sequential I/O bandwidth.  The
-io_tracker counts contiguous I/Os to try to spot when the I/O is in one
-of these sequential modes.  But there are use-cases for wanting to
-promote sequential blocks to the cache (e.g. fast application startup).
-If sequential threshold is set to 0 the sequential I/O detection is
-disabled and sequential I/O will no longer implicitly bypass the cache.
-Setting the random threshold to 0 does _not_ disable the random I/O
-stream detection.
-
-Internally the mq policy determines a promotion threshold.  If the hit
-count of a block not in the cache goes above this threshold it gets
-promoted to the cache.  The read, write and discard promote adjustment
-tunables allow you to tweak the promotion threshold by adding a small
-value based on the io type.  They default to 4, 8 and 1 respectively.
-If you're trying to quickly warm a new cache device you may wish to
-reduce these to encourage promotion.  Remember to switch them back to
-their defaults after the cache fills though.
-
 Stochastic multiqueue (smq)
 ---------------------------
 
index 0a2e7273db9e996ea67d9d461172342aaa65d4f1..2ae40913bbc6addf0325257e5fb0abf44b388c1f 100644 (file)
@@ -304,16 +304,6 @@ config DM_CACHE
          algorithms used to select which blocks are promoted, demoted,
          cleaned etc.  It supports writeback and writethrough modes.
 
-config DM_CACHE_MQ
-       tristate "MQ Cache Policy (EXPERIMENTAL)"
-       depends on DM_CACHE
-       default y
-       ---help---
-         A cache policy that uses a multiqueue ordered by recent hit
-         count to select which blocks should be promoted and demoted.
-         This is meant to be a general purpose policy.  It prioritises
-         reads over writes.
-
 config DM_CACHE_SMQ
        tristate "Stochastic MQ Cache Policy (EXPERIMENTAL)"
        depends on DM_CACHE
index 62a65764e8e0f093cede342f0eb4b7d0aec2eb4e..52ba8dd82821d6f0f3641646863e8234620920dd 100644 (file)
@@ -12,7 +12,6 @@ dm-log-userspace-y \
                += dm-log-userspace-base.o dm-log-userspace-transfer.o
 dm-thin-pool-y += dm-thin.o dm-thin-metadata.o
 dm-cache-y     += dm-cache-target.o dm-cache-metadata.o dm-cache-policy.o
-dm-cache-mq-y   += dm-cache-policy-mq.o
 dm-cache-smq-y   += dm-cache-policy-smq.o
 dm-cache-cleaner-y += dm-cache-policy-cleaner.o
 dm-era-y       += dm-era-target.o
@@ -55,7 +54,6 @@ obj-$(CONFIG_DM_RAID) += dm-raid.o
 obj-$(CONFIG_DM_THIN_PROVISIONING)     += dm-thin-pool.o
 obj-$(CONFIG_DM_VERITY)                += dm-verity.o
 obj-$(CONFIG_DM_CACHE)         += dm-cache.o
-obj-$(CONFIG_DM_CACHE_MQ)      += dm-cache-mq.o
 obj-$(CONFIG_DM_CACHE_SMQ)     += dm-cache-smq.o
 obj-$(CONFIG_DM_CACHE_CLEANER) += dm-cache-cleaner.o
 obj-$(CONFIG_DM_ERA)           += dm-era.o
diff --git a/drivers/md/dm-cache-policy-mq.c b/drivers/md/dm-cache-policy-mq.c
deleted file mode 100644 (file)
index ddb2698..0000000
+++ /dev/null
@@ -1,1473 +0,0 @@
-/*
- * 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/jiffies.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));
-}
-
-/*----------------------------------------------------------------*/
-
-/*
- * 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_iter.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_end_sector(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 void iot_examine_bio(struct io_tracker *t, struct bio *bio)
-{
-       iot_update_stats(t, bio);
-       iot_check_for_pattern_switch(t);
-}
-
-/*----------------------------------------------------------------*/
-
-
-/*
- * This queue is divided up into different levels.  Allowing us to push
- * entries to the back of any of the levels.  Think of it as a partially
- * sorted queue.
- */
-#define NR_QUEUE_LEVELS 16u
-#define NR_SENTINELS NR_QUEUE_LEVELS * 3
-
-#define WRITEBACK_PERIOD HZ
-
-struct queue {
-       unsigned nr_elts;
-       bool current_writeback_sentinels;
-       unsigned long next_writeback;
-       struct list_head qs[NR_QUEUE_LEVELS];
-       struct list_head sentinels[NR_SENTINELS];
-};
-
-static void queue_init(struct queue *q)
-{
-       unsigned i;
-
-       q->nr_elts = 0;
-       q->current_writeback_sentinels = false;
-       q->next_writeback = 0;
-       for (i = 0; i < NR_QUEUE_LEVELS; i++) {
-               INIT_LIST_HEAD(q->qs + i);
-               INIT_LIST_HEAD(q->sentinels + i);
-               INIT_LIST_HEAD(q->sentinels + NR_QUEUE_LEVELS + i);
-               INIT_LIST_HEAD(q->sentinels + (2 * NR_QUEUE_LEVELS) + i);
-       }
-}
-
-static unsigned queue_size(struct queue *q)
-{
-       return q->nr_elts;
-}
-
-static bool queue_empty(struct queue *q)
-{
-       return q->nr_elts == 0;
-}
-
-/*
- * Insert an entry to the back of the given level.
- */
-static void queue_push(struct queue *q, unsigned level, struct list_head *elt)
-{
-       q->nr_elts++;
-       list_add_tail(elt, q->qs + level);
-}
-
-static void queue_remove(struct queue *q, struct list_head *elt)
-{
-       q->nr_elts--;
-       list_del(elt);
-}
-
-static bool is_sentinel(struct queue *q, struct list_head *h)
-{
-       return (h >= q->sentinels) && (h < (q->sentinels + NR_SENTINELS));
-}
-
-/*
- * Gives us the oldest entry of the lowest popoulated level.  If the first
- * level is emptied then we shift down one level.
- */
-static struct list_head *queue_peek(struct queue *q)
-{
-       unsigned level;
-       struct list_head *h;
-
-       for (level = 0; level < NR_QUEUE_LEVELS; level++)
-               list_for_each(h, q->qs + level)
-                       if (!is_sentinel(q, h))
-                               return h;
-
-       return NULL;
-}
-
-static struct list_head *queue_pop(struct queue *q)
-{
-       struct list_head *r = queue_peek(q);
-
-       if (r) {
-               q->nr_elts--;
-               list_del(r);
-       }
-
-       return r;
-}
-
-/*
- * Pops an entry from a level that is not past a sentinel.
- */
-static struct list_head *queue_pop_old(struct queue *q)
-{
-       unsigned level;
-       struct list_head *h;
-
-       for (level = 0; level < NR_QUEUE_LEVELS; level++)
-               list_for_each(h, q->qs + level) {
-                       if (is_sentinel(q, h))
-                               break;
-
-                       q->nr_elts--;
-                       list_del(h);
-                       return h;
-               }
-
-       return NULL;
-}
-
-static struct list_head *list_pop(struct list_head *lh)
-{
-       struct list_head *r = lh->next;
-
-       BUG_ON(!r);
-       list_del_init(r);
-
-       return r;
-}
-
-static struct list_head *writeback_sentinel(struct queue *q, unsigned level)
-{
-       if (q->current_writeback_sentinels)
-               return q->sentinels + NR_QUEUE_LEVELS + level;
-       else
-               return q->sentinels + 2 * NR_QUEUE_LEVELS + level;
-}
-
-static void queue_update_writeback_sentinels(struct queue *q)
-{
-       unsigned i;
-       struct list_head *h;
-
-       if (time_after(jiffies, q->next_writeback)) {
-               for (i = 0; i < NR_QUEUE_LEVELS; i++) {
-                       h = writeback_sentinel(q, i);
-                       list_del(h);
-                       list_add_tail(h, q->qs + i);
-               }
-
-               q->next_writeback = jiffies + WRITEBACK_PERIOD;
-               q->current_writeback_sentinels = !q->current_writeback_sentinels;
-       }
-}
-
-/*
- * Sometimes we want to iterate through entries that have been pushed since
- * a certain event.  We use sentinel entries on the queues to delimit these
- * 'tick' events.
- */
-static void queue_tick(struct queue *q)
-{
-       unsigned i;
-
-       for (i = 0; i < NR_QUEUE_LEVELS; i++) {
-               list_del(q->sentinels + i);
-               list_add_tail(q->sentinels + i, q->qs + i);
-       }
-}
-
-typedef void (*iter_fn)(struct list_head *, void *);
-static void queue_iterate_tick(struct queue *q, iter_fn fn, void *context)
-{
-       unsigned i;
-       struct list_head *h;
-
-       for (i = 0; i < NR_QUEUE_LEVELS; i++) {
-               list_for_each_prev(h, q->qs + i) {
-                       if (is_sentinel(q, h))
-                               break;
-
-                       fn(h, context);
-               }
-       }
-}
-
-/*----------------------------------------------------------------*/
-
-/*
- * Describes a cache entry.  Used in both the cache and the pre_cache.
- */
-struct entry {
-       struct hlist_node hlist;
-       struct list_head list;
-       dm_oblock_t oblock;
-
-       /*
-        * FIXME: pack these better
-        */
-       bool dirty:1;
-       unsigned hit_count;
-};
-
-/*
- * Rather than storing the cblock in an entry, we allocate all entries in
- * an array, and infer the cblock from the entry position.
- *
- * Free entries are linked together into a list.
- */
-struct entry_pool {
-       struct entry *entries, *entries_end;
-       struct list_head free;
-       unsigned nr_allocated;
-};
-
-static int epool_init(struct entry_pool *ep, unsigned nr_entries)
-{
-       unsigned i;
-
-       ep->entries = vzalloc(sizeof(struct entry) * nr_entries);
-       if (!ep->entries)
-               return -ENOMEM;
-
-       ep->entries_end = ep->entries + nr_entries;
-
-       INIT_LIST_HEAD(&ep->free);
-       for (i = 0; i < nr_entries; i++)
-               list_add(&ep->entries[i].list, &ep->free);
-
-       ep->nr_allocated = 0;
-
-       return 0;
-}
-
-static void epool_exit(struct entry_pool *ep)
-{
-       vfree(ep->entries);
-}
-
-static struct entry *alloc_entry(struct entry_pool *ep)
-{
-       struct entry *e;
-
-       if (list_empty(&ep->free))
-               return NULL;
-
-       e = list_entry(list_pop(&ep->free), struct entry, list);
-       INIT_LIST_HEAD(&e->list);
-       INIT_HLIST_NODE(&e->hlist);
-       ep->nr_allocated++;
-
-       return e;
-}
-
-/*
- * This assumes the cblock hasn't already been allocated.
- */
-static struct entry *alloc_particular_entry(struct entry_pool *ep, dm_cblock_t cblock)
-{
-       struct entry *e = ep->entries + from_cblock(cblock);
-
-       list_del_init(&e->list);
-       INIT_HLIST_NODE(&e->hlist);
-       ep->nr_allocated++;
-
-       return e;
-}
-
-static void free_entry(struct entry_pool *ep, struct entry *e)
-{
-       BUG_ON(!ep->nr_allocated);
-       ep->nr_allocated--;
-       INIT_HLIST_NODE(&e->hlist);
-       list_add(&e->list, &ep->free);
-}
-
-/*
- * Returns NULL if the entry is free.
- */
-static struct entry *epool_find(struct entry_pool *ep, dm_cblock_t cblock)
-{
-       struct entry *e = ep->entries + from_cblock(cblock);
-       return !hlist_unhashed(&e->hlist) ? e : NULL;
-}
-
-static bool epool_empty(struct entry_pool *ep)
-{
-       return list_empty(&ep->free);
-}
-
-static bool in_pool(struct entry_pool *ep, struct entry *e)
-{
-       return e >= ep->entries && e < ep->entries_end;
-}
-
-static dm_cblock_t infer_cblock(struct entry_pool *ep, struct entry *e)
-{
-       return to_cblock(e - ep->entries);
-}
-
-/*----------------------------------------------------------------*/
-
-struct mq_policy {
-       struct dm_cache_policy policy;
-
-       /* protects everything */
-       struct mutex lock;
-       dm_cblock_t cache_size;
-       struct io_tracker tracker;
-
-       /*
-        * Entries come from two pools, one of pre-cache entries, and one
-        * for the cache proper.
-        */
-       struct entry_pool pre_cache_pool;
-       struct entry_pool cache_pool;
-
-       /*
-        * We maintain three queues of entries.  The cache proper,
-        * consisting of a clean and dirty queue, contains the currently
-        * active mappings.  Whereas the pre_cache tracks blocks that
-        * are being hit frequently and potential candidates for promotion
-        * to the cache.
-        */
-       struct queue pre_cache;
-       struct queue cache_clean;
-       struct queue cache_dirty;
-
-       /*
-        * 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;
-
-       /*
-        * A count of the number of times the map function has been called
-        * and found an entry in the pre_cache or cache.  Currently used to
-        * calculate the generation.
-        */
-       unsigned hit_count;
-
-       /*
-        * A generation is a longish period that is used to trigger some
-        * book keeping effects.  eg, decrementing hit counts on entries.
-        * This is needed to allow the cache to evolve as io patterns
-        * change.
-        */
-       unsigned generation;
-       unsigned generation_period; /* in lookups (will probably change) */
-
-       unsigned discard_promote_adjustment;
-       unsigned read_promote_adjustment;
-       unsigned write_promote_adjustment;
-
-       /*
-        * The hash table allows us to quickly find an entry by origin
-        * block.  Both pre_cache and cache entries are in here.
-        */
-       unsigned nr_buckets;
-       dm_block_t hash_bits;
-       struct hlist_head *table;
-};
-
-#define DEFAULT_DISCARD_PROMOTE_ADJUSTMENT 1
-#define DEFAULT_READ_PROMOTE_ADJUSTMENT 4
-#define DEFAULT_WRITE_PROMOTE_ADJUSTMENT 8
-#define DISCOURAGE_DEMOTING_DIRTY_THRESHOLD 128
-
-/*----------------------------------------------------------------*/
-
-/*
- * Simple hash table implementation.  Should replace with the standard hash
- * table that's making its way upstream.
- */
-static void hash_insert(struct mq_policy *mq, struct entry *e)
-{
-       unsigned h = hash_64(from_oblock(e->oblock), mq->hash_bits);
-
-       hlist_add_head(&e->hlist, mq->table + h);
-}
-
-static struct entry *hash_lookup(struct mq_policy *mq, dm_oblock_t oblock)
-{
-       unsigned h = hash_64(from_oblock(oblock), mq->hash_bits);
-       struct hlist_head *bucket = mq->table + h;
-       struct entry *e;
-
-       hlist_for_each_entry(e, bucket, hlist)
-               if (e->oblock == oblock) {
-                       hlist_del(&e->hlist);
-                       hlist_add_head(&e->hlist, bucket);
-                       return e;
-               }
-
-       return NULL;
-}
-
-static void hash_remove(struct entry *e)
-{
-       hlist_del(&e->hlist);
-}
-
-/*----------------------------------------------------------------*/
-
-static bool any_free_cblocks(struct mq_policy *mq)
-{
-       return !epool_empty(&mq->cache_pool);
-}
-
-static bool any_clean_cblocks(struct mq_policy *mq)
-{
-       return !queue_empty(&mq->cache_clean);
-}
-
-/*----------------------------------------------------------------*/
-
-/*
- * Now we get to the meat of the policy.  This section deals with deciding
- * when to to add entries to the pre_cache and cache, and move between
- * them.
- */
-
-/*
- * The queue level is based on the log2 of the hit count.
- */
-static unsigned queue_level(struct entry *e)
-{
-       return min((unsigned) ilog2(e->hit_count), NR_QUEUE_LEVELS - 1u);
-}
-
-static bool in_cache(struct mq_policy *mq, struct entry *e)
-{
-       return in_pool(&mq->cache_pool, e);
-}
-
-/*
- * Inserts the entry into the pre_cache or the cache.  Ensures the cache
- * block is marked as allocated if necc.  Inserts into the hash table.
- * Sets the tick which records when the entry was last moved about.
- */
-static void push(struct mq_policy *mq, struct entry *e)
-{
-       hash_insert(mq, e);
-
-       if (in_cache(mq, e))
-               queue_push(e->dirty ? &mq->cache_dirty : &mq->cache_clean,
-                          queue_level(e), &e->list);
-       else
-               queue_push(&mq->pre_cache, queue_level(e), &e->list);
-}
-
-/*
- * Removes an entry from pre_cache or cache.  Removes from the hash table.
- */
-static void del(struct mq_policy *mq, struct entry *e)
-{
-       if (in_cache(mq, e))
-               queue_remove(e->dirty ? &mq->cache_dirty : &mq->cache_clean, &e->list);
-       else
-               queue_remove(&mq->pre_cache, &e->list);
-
-       hash_remove(e);
-}
-
-/*
- * Like del, except it removes the first entry in the queue (ie. the least
- * recently used).
- */
-static struct entry *pop(struct mq_policy *mq, struct queue *q)
-{
-       struct entry *e;
-       struct list_head *h = queue_pop(q);
-
-       if (!h)
-               return NULL;
-
-       e = container_of(h, struct entry, list);
-       hash_remove(e);
-
-       return e;
-}
-
-static struct entry *pop_old(struct mq_policy *mq, struct queue *q)
-{
-       struct entry *e;
-       struct list_head *h = queue_pop_old(q);
-
-       if (!h)
-               return NULL;
-
-       e = container_of(h, struct entry, list);
-       hash_remove(e);
-
-       return e;
-}
-
-static struct entry *peek(struct queue *q)
-{
-       struct list_head *h = queue_peek(q);
-       return h ? container_of(h, struct entry, list) : NULL;
-}
-
-/*
- * The promotion threshold is adjusted every generation.  As are the counts
- * of the entries.
- *
- * At the moment the threshold is taken by averaging the hit counts of some
- * of the entries in the cache (the first 20 entries across all levels in
- * ascending order, giving preference to the clean entries at each level).
- *
- * We can be much cleverer than this though.  For example, each promotion
- * could bump up the threshold helping to prevent churn.  Much more to do
- * here.
- */
-
-#define MAX_TO_AVERAGE 20
-
-static void check_generation(struct mq_policy *mq)
-{
-       unsigned total = 0, nr = 0, count = 0, level;
-       struct list_head *head;
-       struct entry *e;
-
-       if ((mq->hit_count >= mq->generation_period) && (epool_empty(&mq->cache_pool))) {
-               mq->hit_count = 0;
-               mq->generation++;
-
-               for (level = 0; level < NR_QUEUE_LEVELS && count < MAX_TO_AVERAGE; level++) {
-                       head = mq->cache_clean.qs + level;
-                       list_for_each_entry(e, head, list) {
-                               nr++;
-                               total += e->hit_count;
-
-                               if (++count >= MAX_TO_AVERAGE)
-                                       break;
-                       }
-
-                       head = mq->cache_dirty.qs + level;
-                       list_for_each_entry(e, head, list) {
-                               nr++;
-                               total += e->hit_count;
-
-                               if (++count >= MAX_TO_AVERAGE)
-                                       break;
-                       }
-               }
-       }
-}
-
-/*
- * Whenever we use an entry we bump up it's hit counter, and push it to the
- * back to it's current level.
- */
-static void requeue(struct mq_policy *mq, struct entry *e)
-{
-       check_generation(mq);
-       del(mq, e);
-       push(mq, e);
-}
-
-/*
- * Demote the least recently used entry from the cache to the pre_cache.
- * Returns the new cache entry to use, and the old origin block it was
- * mapped to.
- *
- * We drop the hit count on the demoted entry back to 1 to stop it bouncing
- * straight back into the cache if it's subsequently hit.  There are
- * various options here, and more experimentation would be good:
- *
- * - just forget about the demoted entry completely (ie. don't insert it
-     into the pre_cache).
- * - divide the hit count rather that setting to some hard coded value.
- * - set the hit count to a hard coded value other than 1, eg, is it better
- *   if it goes in at level 2?
- */
-static int demote_cblock(struct mq_policy *mq,
-                        struct policy_locker *locker, dm_oblock_t *oblock)
-{
-       struct entry *demoted = peek(&mq->cache_clean);
-
-       if (!demoted)
-               /*
-                * We could get a block from mq->cache_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 the demoted block.
-                */
-               return -EBUSY;
-
-       del(mq, demoted);
-       *oblock = demoted->oblock;
-       free_entry(&mq->cache_pool, demoted);
-
-       /*
-        * We used to put the demoted block into the pre-cache, but I think
-        * it's simpler to just let it work it's way up from zero again.
-        * Stops blocks flickering in and out of the cache.
-        */
-
-       return 0;
-}
-
-/*
- * Entries in the pre_cache whose hit count passes the promotion
- * threshold move to the cache proper.  Working out the correct
- * value for the promotion_threshold is crucial to this policy.
- */
-static unsigned promote_threshold(struct mq_policy *mq)
-{
-       struct entry *e;
-
-       if (any_free_cblocks(mq))
-               return 0;
-
-       e = peek(&mq->cache_clean);
-       if (e)
-               return e->hit_count;
-
-       e = peek(&mq->cache_dirty);
-       if (e)
-               return e->hit_count + DISCOURAGE_DEMOTING_DIRTY_THRESHOLD;
-
-       /* This should never happen */
-       return 0;
-}
-
-/*
- * We modify the basic promotion_threshold depending on the specific io.
- *
- * If the origin block has been discarded then there's no cost to copy it
- * to the cache.
- *
- * We bias towards reads, since they can be demoted at no cost if they
- * haven't been dirtied.
- */
-static unsigned adjusted_promote_threshold(struct mq_policy *mq,
-                                          bool discarded_oblock, int data_dir)
-{
-       if (data_dir == READ)
-               return promote_threshold(mq) + mq->read_promote_adjustment;
-
-       if (discarded_oblock && (any_free_cblocks(mq) || any_clean_cblocks(mq))) {
-               /*
-                * We don't need to do any copying at all, so give this a
-                * very low threshold.
-                */
-               return mq->discard_promote_adjustment;
-       }
-
-       return promote_threshold(mq) + mq->write_promote_adjustment;
-}
-
-static bool should_promote(struct mq_policy *mq, struct entry *e,
-                          bool discarded_oblock, int data_dir)
-{
-       return e->hit_count >=
-               adjusted_promote_threshold(mq, discarded_oblock, data_dir);
-}
-
-static int cache_entry_found(struct mq_policy *mq,
-                            struct entry *e,
-                            struct policy_result *result)
-{
-       requeue(mq, e);
-
-       if (in_cache(mq, e)) {
-               result->op = POLICY_HIT;
-               result->cblock = infer_cblock(&mq->cache_pool, e);
-       }
-
-       return 0;
-}
-
-/*
- * Moves an entry from the pre_cache to the cache.  The main work is
- * finding which cache block to use.
- */
-static int pre_cache_to_cache(struct mq_policy *mq, struct entry *e,
-                             struct policy_locker *locker,
-                             struct policy_result *result)
-{
-       int r;
-       struct entry *new_e;
-
-       /* Ensure there's a free cblock in the cache */
-       if (epool_empty(&mq->cache_pool)) {
-               result->op = POLICY_REPLACE;
-               r = demote_cblock(mq, locker, &result->old_oblock);
-               if (r) {
-                       result->op = POLICY_MISS;
-                       return 0;
-               }
-
-       } else
-               result->op = POLICY_NEW;
-
-       new_e = alloc_entry(&mq->cache_pool);
-       BUG_ON(!new_e);
-
-       new_e->oblock = e->oblock;
-       new_e->dirty = false;
-       new_e->hit_count = e->hit_count;
-
-       del(mq, e);
-       free_entry(&mq->pre_cache_pool, e);
-       push(mq, new_e);
-
-       result->cblock = infer_cblock(&mq->cache_pool, new_e);
-
-       return 0;
-}
-
-static int pre_cache_entry_found(struct mq_policy *mq, struct entry *e,
-                                bool can_migrate, bool discarded_oblock,
-                                int data_dir, struct policy_locker *locker,
-                                struct policy_result *result)
-{
-       int r = 0;
-
-       if (!should_promote(mq, e, discarded_oblock, data_dir)) {
-               requeue(mq, e);
-               result->op = POLICY_MISS;
-
-       } else if (!can_migrate)
-               r = -EWOULDBLOCK;
-
-       else {
-               requeue(mq, e);
-               r = pre_cache_to_cache(mq, e, locker, result);
-       }
-
-       return r;
-}
-
-static void insert_in_pre_cache(struct mq_policy *mq,
-                               dm_oblock_t oblock)
-{
-       struct entry *e = alloc_entry(&mq->pre_cache_pool);
-
-       if (!e)
-               /*
-                * There's no spare entry structure, so we grab the least
-                * used one from the pre_cache.
-                */
-               e = pop(mq, &mq->pre_cache);
-
-       if (unlikely(!e)) {
-               DMWARN("couldn't pop from pre cache");
-               return;
-       }
-
-       e->dirty = false;
-       e->oblock = oblock;
-       e->hit_count = 1;
-       push(mq, e);
-}
-
-static void insert_in_cache(struct mq_policy *mq, dm_oblock_t oblock,
-                           struct policy_locker *locker,
-                           struct policy_result *result)
-{
-       int r;
-       struct entry *e;
-
-       if (epool_empty(&mq->cache_pool)) {
-               result->op = POLICY_REPLACE;
-               r = demote_cblock(mq, locker, &result->old_oblock);
-               if (unlikely(r)) {
-                       result->op = POLICY_MISS;
-                       insert_in_pre_cache(mq, oblock);
-                       return;
-               }
-
-               /*
-                * This will always succeed, since we've just demoted.
-                */
-               e = alloc_entry(&mq->cache_pool);
-               BUG_ON(!e);
-
-       } else {
-               e = alloc_entry(&mq->cache_pool);
-               result->op = POLICY_NEW;
-       }
-
-       e->oblock = oblock;
-       e->dirty = false;
-       e->hit_count = 1;
-       push(mq, e);
-
-       result->cblock = infer_cblock(&mq->cache_pool, e);
-}
-
-static int no_entry_found(struct mq_policy *mq, dm_oblock_t oblock,
-                         bool can_migrate, bool discarded_oblock,
-                         int data_dir, struct policy_locker *locker,
-                         struct policy_result *result)
-{
-       if (adjusted_promote_threshold(mq, discarded_oblock, data_dir) <= 1) {
-               if (can_migrate)
-                       insert_in_cache(mq, oblock, locker, result);
-               else
-                       return -EWOULDBLOCK;
-       } else {
-               insert_in_pre_cache(mq, oblock);
-               result->op = POLICY_MISS;
-       }
-
-       return 0;
-}
-
-/*
- * Looks the oblock up in the hash table, then decides whether to put in
- * pre_cache, or cache etc.
- */
-static int map(struct mq_policy *mq, dm_oblock_t oblock,
-              bool can_migrate, bool discarded_oblock,
-              int data_dir, struct policy_locker *locker,
-              struct policy_result *result)
-{
-       int r = 0;
-       struct entry *e = hash_lookup(mq, oblock);
-
-       if (e && in_cache(mq, e))
-               r = cache_entry_found(mq, e, result);
-
-       else if (mq->tracker.thresholds[PATTERN_SEQUENTIAL] &&
-                iot_pattern(&mq->tracker) == PATTERN_SEQUENTIAL)
-               result->op = POLICY_MISS;
-
-       else if (e)
-               r = pre_cache_entry_found(mq, e, can_migrate, discarded_oblock,
-                                         data_dir, locker, result);
-
-       else
-               r = no_entry_found(mq, oblock, can_migrate, discarded_oblock,
-                                  data_dir, locker, result);
-
-       if (r == -EWOULDBLOCK)
-               result->op = POLICY_MISS;
-
-       return r;
-}
-
-/*----------------------------------------------------------------*/
-
-/*
- * Public interface, via the policy struct.  See dm-cache-policy.h for a
- * description of these.
- */
-
-static struct mq_policy *to_mq_policy(struct dm_cache_policy *p)
-{
-       return container_of(p, struct mq_policy, policy);
-}
-
-static void mq_destroy(struct dm_cache_policy *p)
-{
-       struct mq_policy *mq = to_mq_policy(p);
-
-       vfree(mq->table);
-       epool_exit(&mq->cache_pool);
-       epool_exit(&mq->pre_cache_pool);
-       kfree(mq);
-}
-
-static void update_pre_cache_hits(struct list_head *h, void *context)
-{
-       struct entry *e = container_of(h, struct entry, list);
-       e->hit_count++;
-}
-
-static void update_cache_hits(struct list_head *h, void *context)
-{
-       struct mq_policy *mq = context;
-       struct entry *e = container_of(h, struct entry, list);
-       e->hit_count++;
-       mq->hit_count++;
-}
-
-static void copy_tick(struct mq_policy *mq)
-{
-       unsigned long flags, tick;
-
-       spin_lock_irqsave(&mq->tick_lock, flags);
-       tick = mq->tick_protected;
-       if (tick != mq->tick) {
-               queue_iterate_tick(&mq->pre_cache, update_pre_cache_hits, mq);
-               queue_iterate_tick(&mq->cache_dirty, update_cache_hits, mq);
-               queue_iterate_tick(&mq->cache_clean, update_cache_hits, mq);
-               mq->tick = tick;
-       }
-
-       queue_tick(&mq->pre_cache);
-       queue_tick(&mq->cache_dirty);
-       queue_tick(&mq->cache_clean);
-       queue_update_writeback_sentinels(&mq->cache_dirty);
-       spin_unlock_irqrestore(&mq->tick_lock, flags);
-}
-
-static int mq_map(struct dm_cache_policy *p, dm_oblock_t oblock,
-                 bool can_block, bool can_migrate, bool discarded_oblock,
-                 struct bio *bio, struct policy_locker *locker,
-                 struct policy_result *result)
-{
-       int r;
-       struct mq_policy *mq = to_mq_policy(p);
-
-       result->op = POLICY_MISS;
-
-       if (can_block)
-               mutex_lock(&mq->lock);
-       else if (!mutex_trylock(&mq->lock))
-               return -EWOULDBLOCK;
-
-       copy_tick(mq);
-
-       iot_examine_bio(&mq->tracker, bio);
-       r = map(mq, oblock, can_migrate, discarded_oblock,
-               bio_data_dir(bio), locker, result);
-
-       mutex_unlock(&mq->lock);
-
-       return r;
-}
-
-static int mq_lookup(struct dm_cache_policy *p, dm_oblock_t oblock, dm_cblock_t *cblock)
-{
-       int r;
-       struct mq_policy *mq = to_mq_policy(p);
-       struct entry *e;
-
-       if (!mutex_trylock(&mq->lock))
-               return -EWOULDBLOCK;
-
-       e = hash_lookup(mq, oblock);
-       if (e && in_cache(mq, e)) {
-               *cblock = infer_cblock(&mq->cache_pool, e);
-               r = 0;
-       } else
-               r = -ENOENT;
-
-       mutex_unlock(&mq->lock);
-
-       return r;
-}
-
-static void __mq_set_clear_dirty(struct mq_policy *mq, dm_oblock_t oblock, bool set)
-{
-       struct entry *e;
-
-       e = hash_lookup(mq, oblock);
-       BUG_ON(!e || !in_cache(mq, e));
-
-       del(mq, e);
-       e->dirty = set;
-       push(mq, e);
-}
-
-static void mq_set_dirty(struct dm_cache_policy *p, dm_oblock_t oblock)
-{
-       struct mq_policy *mq = to_mq_policy(p);
-
-       mutex_lock(&mq->lock);
-       __mq_set_clear_dirty(mq, oblock, true);
-       mutex_unlock(&mq->lock);
-}
-
-static void mq_clear_dirty(struct dm_cache_policy *p, dm_oblock_t oblock)
-{
-       struct mq_policy *mq = to_mq_policy(p);
-
-       mutex_lock(&mq->lock);
-       __mq_set_clear_dirty(mq, oblock, false);
-       mutex_unlock(&mq->lock);
-}
-
-static int mq_load_mapping(struct dm_cache_policy *p,
-                          dm_oblock_t oblock, dm_cblock_t cblock,
-                          uint32_t hint, bool hint_valid)
-{
-       struct mq_policy *mq = to_mq_policy(p);
-       struct entry *e;
-
-       e = alloc_particular_entry(&mq->cache_pool, cblock);
-       e->oblock = oblock;
-       e->dirty = false;       /* this gets corrected in a minute */
-       e->hit_count = hint_valid ? hint : 1;
-       push(mq, e);
-
-       return 0;
-}
-
-static int mq_save_hints(struct mq_policy *mq, struct queue *q,
-                        policy_walk_fn fn, void *context)
-{
-       int r;
-       unsigned level;
-       struct list_head *h;
-       struct entry *e;
-
-       for (level = 0; level < NR_QUEUE_LEVELS; level++)
-               list_for_each(h, q->qs + level) {
-                       if (is_sentinel(q, h))
-                               continue;
-
-                       e = container_of(h, struct entry, list);
-                       r = fn(context, infer_cblock(&mq->cache_pool, e),
-                              e->oblock, e->hit_count);
-                       if (r)
-                               return r;
-               }
-
-       return 0;
-}
-
-static int mq_walk_mappings(struct dm_cache_policy *p, policy_walk_fn fn,
-                           void *context)
-{
-       struct mq_policy *mq = to_mq_policy(p);
-       int r = 0;
-
-       mutex_lock(&mq->lock);
-
-       r = mq_save_hints(mq, &mq->cache_clean, fn, context);
-       if (!r)
-               r = mq_save_hints(mq, &mq->cache_dirty, fn, context);
-
-       mutex_unlock(&mq->lock);
-
-       return r;
-}
-
-static void __remove_mapping(struct mq_policy *mq, dm_oblock_t oblock)
-{
-       struct entry *e;
-
-       e = hash_lookup(mq, oblock);
-       BUG_ON(!e || !in_cache(mq, e));
-
-       del(mq, e);
-       free_entry(&mq->cache_pool, e);
-}
-
-static void mq_remove_mapping(struct dm_cache_policy *p, dm_oblock_t oblock)
-{
-       struct mq_policy *mq = to_mq_policy(p);
-
-       mutex_lock(&mq->lock);
-       __remove_mapping(mq, oblock);
-       mutex_unlock(&mq->lock);
-}
-
-static int __remove_cblock(struct mq_policy *mq, dm_cblock_t cblock)
-{
-       struct entry *e = epool_find(&mq->cache_pool, cblock);
-
-       if (!e)
-               return -ENODATA;
-
-       del(mq, e);
-       free_entry(&mq->cache_pool, e);
-
-       return 0;
-}
-
-static int mq_remove_cblock(struct dm_cache_policy *p, dm_cblock_t cblock)
-{
-       int r;
-       struct mq_policy *mq = to_mq_policy(p);
-
-       mutex_lock(&mq->lock);
-       r = __remove_cblock(mq, cblock);
-       mutex_unlock(&mq->lock);
-
-       return r;
-}
-
-#define CLEAN_TARGET_PERCENTAGE 25
-
-static bool clean_target_met(struct mq_policy *mq)
-{
-       /*
-        * 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) - queue_size(&mq->cache_dirty);
-       unsigned target = from_cblock(mq->cache_size) * CLEAN_TARGET_PERCENTAGE / 100;
-
-       return nr_clean >= target;
-}
-
-static int __mq_writeback_work(struct mq_policy *mq, dm_oblock_t *oblock,
-                             dm_cblock_t *cblock)
-{
-       struct entry *e = pop_old(mq, &mq->cache_dirty);
-
-       if (!e && !clean_target_met(mq))
-               e = pop(mq, &mq->cache_dirty);
-
-       if (!e)
-               return -ENODATA;
-
-       *oblock = e->oblock;
-       *cblock = infer_cblock(&mq->cache_pool, e);
-       e->dirty = false;
-       push(mq, e);
-
-       return 0;
-}
-
-static int mq_writeback_work(struct dm_cache_policy *p, dm_oblock_t *oblock,
-                            dm_cblock_t *cblock, bool critical_only)
-{
-       int r;
-       struct mq_policy *mq = to_mq_policy(p);
-
-       mutex_lock(&mq->lock);
-       r = __mq_writeback_work(mq, oblock, cblock);
-       mutex_unlock(&mq->lock);
-
-       return r;
-}
-
-static void __force_mapping(struct mq_policy *mq,
-                           dm_oblock_t current_oblock, dm_oblock_t new_oblock)
-{
-       struct entry *e = hash_lookup(mq, current_oblock);
-
-       if (e && in_cache(mq, e)) {
-               del(mq, e);
-               e->oblock = new_oblock;
-               e->dirty = true;
-               push(mq, e);
-       }
-}
-
-static void mq_force_mapping(struct dm_cache_policy *p,
-                            dm_oblock_t current_oblock, dm_oblock_t new_oblock)
-{
-       struct mq_policy *mq = to_mq_policy(p);
-
-       mutex_lock(&mq->lock);
-       __force_mapping(mq, current_oblock, new_oblock);
-       mutex_unlock(&mq->lock);
-}
-
-static dm_cblock_t mq_residency(struct dm_cache_policy *p)
-{
-       dm_cblock_t r;
-       struct mq_policy *mq = to_mq_policy(p);
-
-       mutex_lock(&mq->lock);
-       r = to_cblock(mq->cache_pool.nr_allocated);
-       mutex_unlock(&mq->lock);
-
-       return r;
-}
-
-static void mq_tick(struct dm_cache_policy *p, bool can_block)
-{
-       struct mq_policy *mq = to_mq_policy(p);
-       unsigned long flags;
-
-       spin_lock_irqsave(&mq->tick_lock, flags);
-       mq->tick_protected++;
-       spin_unlock_irqrestore(&mq->tick_lock, flags);
-
-       if (can_block) {
-               mutex_lock(&mq->lock);
-               copy_tick(mq);
-               mutex_unlock(&mq->lock);
-       }
-}
-
-static int mq_set_config_value(struct dm_cache_policy *p,
-                              const char *key, const char *value)
-{
-       struct mq_policy *mq = to_mq_policy(p);
-       unsigned long tmp;
-
-       if (kstrtoul(value, 10, &tmp))
-               return -EINVAL;
-
-       if (!strcasecmp(key, "random_threshold")) {
-               mq->tracker.thresholds[PATTERN_RANDOM] = tmp;
-
-       } else if (!strcasecmp(key, "sequential_threshold")) {
-               mq->tracker.thresholds[PATTERN_SEQUENTIAL] = tmp;
-
-       } else if (!strcasecmp(key, "discard_promote_adjustment"))
-               mq->discard_promote_adjustment = tmp;
-
-       else if (!strcasecmp(key, "read_promote_adjustment"))
-               mq->read_promote_adjustment = tmp;
-
-       else if (!strcasecmp(key, "write_promote_adjustment"))
-               mq->write_promote_adjustment = tmp;
-
-       else
-               return -EINVAL;
-
-       return 0;
-}
-
-static int mq_emit_config_values(struct dm_cache_policy *p, char *result,
-                                unsigned maxlen, ssize_t *sz_ptr)
-{
-       ssize_t sz = *sz_ptr;
-       struct mq_policy *mq = to_mq_policy(p);
-
-       DMEMIT("10 random_threshold %u "
-              "sequential_threshold %u "
-              "discard_promote_adjustment %u "
-              "read_promote_adjustment %u "
-              "write_promote_adjustment %u ",
-              mq->tracker.thresholds[PATTERN_RANDOM],
-              mq->tracker.thresholds[PATTERN_SEQUENTIAL],
-              mq->discard_promote_adjustment,
-              mq->read_promote_adjustment,
-              mq->write_promote_adjustment);
-
-       *sz_ptr = sz;
-       return 0;
-}
-
-/* Init the policy plugin interface function pointers. */
-static void init_policy_functions(struct mq_policy *mq)
-{
-       mq->policy.destroy = mq_destroy;
-       mq->policy.map = mq_map;
-       mq->policy.lookup = mq_lookup;
-       mq->policy.set_dirty = mq_set_dirty;
-       mq->policy.clear_dirty = mq_clear_dirty;
-       mq->policy.load_mapping = mq_load_mapping;
-       mq->policy.walk_mappings = mq_walk_mappings;
-       mq->policy.remove_mapping = mq_remove_mapping;
-       mq->policy.remove_cblock = mq_remove_cblock;
-       mq->policy.writeback_work = mq_writeback_work;
-       mq->policy.force_mapping = mq_force_mapping;
-       mq->policy.residency = mq_residency;
-       mq->policy.tick = mq_tick;
-       mq->policy.emit_config_values = mq_emit_config_values;
-       mq->policy.set_config_value = mq_set_config_value;
-}
-
-static struct dm_cache_policy *mq_create(dm_cblock_t cache_size,
-                                        sector_t origin_size,
-                                        sector_t cache_block_size)
-{
-       struct mq_policy *mq = kzalloc(sizeof(*mq), GFP_KERNEL);
-
-       if (!mq)
-               return NULL;
-
-       init_policy_functions(mq);
-       iot_init(&mq->tracker, SEQUENTIAL_THRESHOLD_DEFAULT, RANDOM_THRESHOLD_DEFAULT);
-       mq->cache_size = cache_size;
-
-       if (epool_init(&mq->pre_cache_pool, from_cblock(cache_size))) {
-               DMERR("couldn't initialize pool of pre-cache entries");
-               goto bad_pre_cache_init;
-       }
-
-       if (epool_init(&mq->cache_pool, from_cblock(cache_size))) {
-               DMERR("couldn't initialize pool of cache entries");
-               goto bad_cache_init;
-       }
-
-       mq->tick_protected = 0;
-       mq->tick = 0;
-       mq->hit_count = 0;
-       mq->generation = 0;
-       mq->discard_promote_adjustment = DEFAULT_DISCARD_PROMOTE_ADJUSTMENT;
-       mq->read_promote_adjustment = DEFAULT_READ_PROMOTE_ADJUSTMENT;
-       mq->write_promote_adjustment = DEFAULT_WRITE_PROMOTE_ADJUSTMENT;
-       mutex_init(&mq->lock);
-       spin_lock_init(&mq->tick_lock);
-
-       queue_init(&mq->pre_cache);
-       queue_init(&mq->cache_clean);
-       queue_init(&mq->cache_dirty);
-
-       mq->generation_period = max((unsigned) from_cblock(cache_size), 1024U);
-
-       mq->nr_buckets = next_power(from_cblock(cache_size) / 2, 16);
-       mq->hash_bits = __ffs(mq->nr_buckets);
-       mq->table = vzalloc(sizeof(*mq->table) * mq->nr_buckets);
-       if (!mq->table)
-               goto bad_alloc_table;
-
-       return &mq->policy;
-
-bad_alloc_table:
-       epool_exit(&mq->cache_pool);
-bad_cache_init:
-       epool_exit(&mq->pre_cache_pool);
-bad_pre_cache_init:
-       kfree(mq);
-
-       return NULL;
-}
-
-/*----------------------------------------------------------------*/
-
-static struct dm_cache_policy_type mq_policy_type = {
-       .name = "mq",
-       .version = {1, 4, 0},
-       .hint_size = 4,
-       .owner = THIS_MODULE,
-       .create = mq_create
-};
-
-static int __init mq_init(void)
-{
-       int r;
-
-       mq_entry_cache = kmem_cache_create("dm_mq_policy_cache_entry",
-                                          sizeof(struct entry),
-                                          __alignof__(struct entry),
-                                          0, NULL);
-       if (!mq_entry_cache)
-               return -ENOMEM;
-
-       r = dm_cache_policy_register(&mq_policy_type);
-       if (r) {
-               DMERR("register failed %d", r);
-               kmem_cache_destroy(mq_entry_cache);
-               return -ENOMEM;
-       }
-
-       return 0;
-}
-
-static void __exit mq_exit(void)
-{
-       dm_cache_policy_unregister(&mq_policy_type);
-
-       kmem_cache_destroy(mq_entry_cache);
-}
-
-module_init(mq_init);
-module_exit(mq_exit);
-
-MODULE_AUTHOR("Joe Thornber <dm-devel@redhat.com>");
-MODULE_LICENSE("GPL");
-MODULE_DESCRIPTION("mq cache policy");
index 28d4586748d0033e1a2940bd8688b72ba34e84e5..a3e8e747b94f57c02c123b2f0db02324bc2df7cb 100644 (file)
@@ -1567,8 +1567,48 @@ static void smq_tick(struct dm_cache_policy *p, bool can_block)
        spin_unlock_irqrestore(&mq->lock, flags);
 }
 
+/*
+ * smq has no config values, but the old mq policy did.  To avoid breaking
+ * software we continue to accept these configurables for the mq policy,
+ * but they have no effect.
+ */
+static int mq_set_config_value(struct dm_cache_policy *p,
+                              const char *key, const char *value)
+{
+       unsigned long tmp;
+
+       if (kstrtoul(value, 10, &tmp))
+               return -EINVAL;
+
+       if (!strcasecmp(key, "random_threshold") ||
+           !strcasecmp(key, "sequential_threshold") ||
+           !strcasecmp(key, "discard_promote_adjustment") ||
+           !strcasecmp(key, "read_promote_adjustment") ||
+           !strcasecmp(key, "write_promote_adjustment")) {
+               DMWARN("tunable '%s' no longer has any effect, mq policy is now an alias for smq", key);
+               return 0;
+       }
+
+       return -EINVAL;
+}
+
+static int mq_emit_config_values(struct dm_cache_policy *p, char *result,
+                                unsigned maxlen, ssize_t *sz_ptr)
+{
+       ssize_t sz = *sz_ptr;
+
+       DMEMIT("10 random_threshold 0 "
+              "sequential_threshold 0 "
+              "discard_promote_adjustment 0 "
+              "read_promote_adjustment 0 "
+              "write_promote_adjustment 0 ");
+
+       *sz_ptr = sz;
+       return 0;
+}
+
 /* Init the policy plugin interface function pointers. */
-static void init_policy_functions(struct smq_policy *mq)
+static void init_policy_functions(struct smq_policy *mq, bool mimic_mq)
 {
        mq->policy.destroy = smq_destroy;
        mq->policy.map = smq_map;
@@ -1583,6 +1623,11 @@ static void init_policy_functions(struct smq_policy *mq)
        mq->policy.force_mapping = smq_force_mapping;
        mq->policy.residency = smq_residency;
        mq->policy.tick = smq_tick;
+
+       if (mimic_mq) {
+               mq->policy.set_config_value = mq_set_config_value;
+               mq->policy.emit_config_values = mq_emit_config_values;
+       }
 }
 
 static bool too_many_hotspot_blocks(sector_t origin_size,
@@ -1606,9 +1651,10 @@ static void calc_hotspot_params(sector_t origin_size,
                *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)
+static struct dm_cache_policy *__smq_create(dm_cblock_t cache_size,
+                                           sector_t origin_size,
+                                           sector_t cache_block_size,
+                                           bool mimic_mq)
 {
        unsigned i;
        unsigned nr_sentinels_per_queue = 2u * NR_CACHE_LEVELS;
@@ -1618,7 +1664,7 @@ static struct dm_cache_policy *smq_create(dm_cblock_t cache_size,
        if (!mq)
                return NULL;
 
-       init_policy_functions(mq);
+       init_policy_functions(mq, mimic_mq);
        mq->cache_size = cache_size;
        mq->cache_block_size = cache_block_size;
 
@@ -1706,19 +1752,41 @@ bad_pool_init:
        return NULL;
 }
 
+static struct dm_cache_policy *smq_create(dm_cblock_t cache_size,
+                                         sector_t origin_size,
+                                         sector_t cache_block_size)
+{
+       return __smq_create(cache_size, origin_size, cache_block_size, false);
+}
+
+static struct dm_cache_policy *mq_create(dm_cblock_t cache_size,
+                                        sector_t origin_size,
+                                        sector_t cache_block_size)
+{
+       return __smq_create(cache_size, origin_size, cache_block_size, true);
+}
+
 /*----------------------------------------------------------------*/
 
 static struct dm_cache_policy_type smq_policy_type = {
        .name = "smq",
-       .version = {1, 0, 0},
+       .version = {1, 5, 0},
        .hint_size = 4,
        .owner = THIS_MODULE,
        .create = smq_create
 };
 
+static struct dm_cache_policy_type mq_policy_type = {
+       .name = "mq",
+       .version = {1, 5, 0},
+       .hint_size = 4,
+       .owner = THIS_MODULE,
+       .create = mq_create,
+};
+
 static struct dm_cache_policy_type default_policy_type = {
        .name = "default",
-       .version = {1, 4, 0},
+       .version = {1, 5, 0},
        .hint_size = 4,
        .owner = THIS_MODULE,
        .create = smq_create,
@@ -1735,9 +1803,17 @@ static int __init smq_init(void)
                return -ENOMEM;
        }
 
+       r = dm_cache_policy_register(&mq_policy_type);
+       if (r) {
+               DMERR("register failed %d", r);
+               dm_cache_policy_unregister(&smq_policy_type);
+               return -ENOMEM;
+       }
+
        r = dm_cache_policy_register(&default_policy_type);
        if (r) {
                DMERR("register failed (as default) %d", r);
+               dm_cache_policy_unregister(&mq_policy_type);
                dm_cache_policy_unregister(&smq_policy_type);
                return -ENOMEM;
        }
@@ -1748,6 +1824,7 @@ static int __init smq_init(void)
 static void __exit smq_exit(void)
 {
        dm_cache_policy_unregister(&smq_policy_type);
+       dm_cache_policy_unregister(&mq_policy_type);
        dm_cache_policy_unregister(&default_policy_type);
 }
 
@@ -1759,3 +1836,4 @@ MODULE_LICENSE("GPL");
 MODULE_DESCRIPTION("smq cache policy");
 
 MODULE_ALIAS("dm-cache-default");
+MODULE_ALIAS("dm-cache-mq");