dm bio prison: implement per bucket locking in the dm_bio_prison hash table

Split the single per bio-prison lock by using per bucket locking.  Per
bucket locking benefits both dm-thin and dm-cache targets by reducing
bio-prison lock contention.

Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/drivers/md/dm-bio-prison.c b/drivers/md/dm-bio-prison.c
index 7143438..f752d12 100644 (file)
--- a/drivers/md/dm-bio-prison.c
+++ b/drivers/md/dm-bio-prison.c
@@ -14,13 +14,17 @@
 
 /*----------------------------------------------------------------*/
 
-struct dm_bio_prison {
+struct bucket {
        spinlock_t lock;
+       struct hlist_head cells;
+};
+
+struct dm_bio_prison {
        mempool_t *cell_pool;
 
        unsigned nr_buckets;
        unsigned hash_mask;
-       struct hlist_head *cells;
+       struct bucket *buckets;
 };
 
 /*----------------------------------------------------------------*/
@@ -40,6 +44,12 @@ static uint32_t calc_nr_buckets(unsigned nr_cells)
 
 static struct kmem_cache *_cell_cache;
 
+static void init_bucket(struct bucket *b)
+{
+       spin_lock_init(&b->lock);
+       INIT_HLIST_HEAD(&b->cells);
+}
+
 /*
  * @nr_cells should be the number of cells you want in use _concurrently_.
  * Don't confuse it with the number of distinct keys.
@@ -49,13 +59,12 @@ struct dm_bio_prison *dm_bio_prison_create(unsigned nr_cells)
        unsigned i;
        uint32_t nr_buckets = calc_nr_buckets(nr_cells);
        size_t len = sizeof(struct dm_bio_prison) +
-               (sizeof(struct hlist_head) * nr_buckets);
+               (sizeof(struct bucket) * nr_buckets);
        struct dm_bio_prison *prison = kmalloc(len, GFP_KERNEL);
 
        if (!prison)
                return NULL;
 
-       spin_lock_init(&prison->lock);
        prison->cell_pool = mempool_create_slab_pool(nr_cells, _cell_cache);
        if (!prison->cell_pool) {
                kfree(prison);
@@ -64,9 +73,9 @@ struct dm_bio_prison *dm_bio_prison_create(unsigned nr_cells)
 
        prison->nr_buckets = nr_buckets;
        prison->hash_mask = nr_buckets - 1;
-       prison->cells = (struct hlist_head *) (prison + 1);
+       prison->buckets = (struct bucket *) (prison + 1);
        for (i = 0; i < nr_buckets; i++)
-               INIT_HLIST_HEAD(prison->cells + i);
+               init_bucket(prison->buckets + i);
 
        return prison;
 }
@@ -107,40 +116,44 @@ static int keys_equal(struct dm_cell_key *lhs, struct dm_cell_key *rhs)
                       (lhs->block == rhs->block);
 }
 
-static struct dm_bio_prison_cell *__search_bucket(struct hlist_head *bucket,
+static struct bucket *get_bucket(struct dm_bio_prison *prison,
+                                struct dm_cell_key *key)
+{
+       return prison->buckets + hash_key(prison, key);
+}
+
+static struct dm_bio_prison_cell *__search_bucket(struct bucket *b,
                                                  struct dm_cell_key *key)
 {
        struct dm_bio_prison_cell *cell;
 
-       hlist_for_each_entry(cell, bucket, list)
+       hlist_for_each_entry(cell, &b->cells, list)
                if (keys_equal(&cell->key, key))
                        return cell;
 
        return NULL;
 }
 
-static void __setup_new_cell(struct dm_bio_prison *prison,
+static void __setup_new_cell(struct bucket *b,
                             struct dm_cell_key *key,
                             struct bio *holder,
-                            uint32_t hash,
                             struct dm_bio_prison_cell *cell)
 {
        memcpy(&cell->key, key, sizeof(cell->key));
        cell->holder = holder;
        bio_list_init(&cell->bios);
-       hlist_add_head(&cell->list, prison->cells + hash);
+       hlist_add_head(&cell->list, &b->cells);
 }
 
-static int __bio_detain(struct dm_bio_prison *prison,
+static int __bio_detain(struct bucket *b,
                        struct dm_cell_key *key,
                        struct bio *inmate,
                        struct dm_bio_prison_cell *cell_prealloc,
                        struct dm_bio_prison_cell **cell_result)
 {
-       uint32_t hash = hash_key(prison, key);
        struct dm_bio_prison_cell *cell;
 
-       cell = __search_bucket(prison->cells + hash, key);
+       cell = __search_bucket(b, key);
        if (cell) {
                if (inmate)
                        bio_list_add(&cell->bios, inmate);
@@ -148,7 +161,7 @@ static int __bio_detain(struct dm_bio_prison *prison,
                return 1;
        }
 
-       __setup_new_cell(prison, key, inmate, hash, cell_prealloc);
+       __setup_new_cell(b, key, inmate, cell_prealloc);
        *cell_result = cell_prealloc;
        return 0;
 }
@@ -161,10 +174,11 @@ static int bio_detain(struct dm_bio_prison *prison,
 {
        int r;
        unsigned long flags;
+       struct bucket *b = get_bucket(prison, key);
 
-       spin_lock_irqsave(&prison->lock, flags);
-       r = __bio_detain(prison, key, inmate, cell_prealloc, cell_result);
-       spin_unlock_irqrestore(&prison->lock, flags);
+       spin_lock_irqsave(&b->lock, flags);
+       r = __bio_detain(b, key, inmate, cell_prealloc, cell_result);
+       spin_unlock_irqrestore(&b->lock, flags);
 
        return r;
 }
@@ -208,10 +222,11 @@ void dm_cell_release(struct dm_bio_prison *prison,
                     struct bio_list *bios)
 {
        unsigned long flags;
+       struct bucket *b = get_bucket(prison, &cell->key);
 
-       spin_lock_irqsave(&prison->lock, flags);
+       spin_lock_irqsave(&b->lock, flags);
        __cell_release(cell, bios);
-       spin_unlock_irqrestore(&prison->lock, flags);
+       spin_unlock_irqrestore(&b->lock, flags);
 }
 EXPORT_SYMBOL_GPL(dm_cell_release);
 
@@ -230,10 +245,11 @@ void dm_cell_release_no_holder(struct dm_bio_prison *prison,
                               struct bio_list *inmates)
 {
        unsigned long flags;
+       struct bucket *b = get_bucket(prison, &cell->key);
 
-       spin_lock_irqsave(&prison->lock, flags);
+       spin_lock_irqsave(&b->lock, flags);
        __cell_release_no_holder(cell, inmates);
-       spin_unlock_irqrestore(&prison->lock, flags);
+       spin_unlock_irqrestore(&b->lock, flags);
 }
 EXPORT_SYMBOL_GPL(dm_cell_release_no_holder);
 
@@ -242,13 +258,9 @@ void dm_cell_error(struct dm_bio_prison *prison,
 {
        struct bio_list bios;
        struct bio *bio;
-       unsigned long flags;
 
        bio_list_init(&bios);
-
-       spin_lock_irqsave(&prison->lock, flags);
-       __cell_release(cell, &bios);
-       spin_unlock_irqrestore(&prison->lock, flags);
+       dm_cell_release(prison, cell, &bios);
 
        while ((bio = bio_list_pop(&bios)))
                bio_endio(bio, error);