dm transaction manager: add support for prefetching blocks of metadata

Introduce the dm_tm_issue_prefetches interface.  If you're using a
non-blocking clone the tm will build up a list of requested blocks that
weren't in core.  dm_tm_issue_prefetches will request those blocks to be
prefetched.

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

2 files changed, 82 insertions, 2 deletions

diff --git a/drivers/md/persistent-data/dm-transaction-manager.c b/drivers/md/persistent-data/dm-transaction-manager.c
index 3bc30a0ae3d6..9cb797d800cf 100644
--- a/drivers/md/persistent-data/dm-transaction-manager.c
+++ b/drivers/md/persistent-data/dm-transaction-manager.c
@@ -10,6 +10,8 @@
 #include "dm-persistent-data-internal.h"
 
 #include <linux/export.h>
+#include <linux/mutex.h>
+#include <linux/hash.h>
 #include <linux/slab.h>
 #include <linux/device-mapper.h>
 
@@ -17,6 +19,61 @@
 
 /*----------------------------------------------------------------*/
 
+#define PREFETCH_SIZE 128
+#define PREFETCH_BITS 7
+#define PREFETCH_SENTINEL ((dm_block_t) -1ULL)
+
+struct prefetch_set {
+        struct mutex lock;
+        dm_block_t blocks[PREFETCH_SIZE];
+};
+
+static unsigned prefetch_hash(dm_block_t b)
+{
+        return hash_64(b, PREFETCH_BITS);
+}
+
+static void prefetch_wipe(struct prefetch_set *p)
+{
+        unsigned i;
+        for (i = 0; i < PREFETCH_SIZE; i++)
+                p->blocks[i] = PREFETCH_SENTINEL;
+}
+
+static void prefetch_init(struct prefetch_set *p)
+{
+        mutex_init(&p->lock);
+        prefetch_wipe(p);
+}
+
+static void prefetch_add(struct prefetch_set *p, dm_block_t b)
+{
+        unsigned h = prefetch_hash(b);
+
+        mutex_lock(&p->lock);
+        if (p->blocks[h] == PREFETCH_SENTINEL)
+                p->blocks[h] = b;
+
+        mutex_unlock(&p->lock);
+}
+
+static void prefetch_issue(struct prefetch_set *p, struct dm_block_manager *bm)
+{
+        unsigned i;
+
+        mutex_lock(&p->lock);
+
+        for (i = 0; i < PREFETCH_SIZE; i++)
+                if (p->blocks[i] != PREFETCH_SENTINEL) {
+                        dm_bm_prefetch(bm, p->blocks[i]);
+                        p->blocks[i] = PREFETCH_SENTINEL;
+                }
+
+        mutex_unlock(&p->lock);
+}
+
+/*----------------------------------------------------------------*/
+
 struct shadow_info {
         struct hlist_node hlist;
         dm_block_t where;
@@ -37,6 +94,8 @@ struct dm_transaction_manager {
 
         spinlock_t lock;
         struct hlist_head buckets[DM_HASH_SIZE];
+
+        struct prefetch_set prefetches;
 };
 
 /*----------------------------------------------------------------*/
@@ -117,6 +176,8 @@ static struct dm_transaction_manager *dm_tm_create(struct dm_block_manager *bm,
         for (i = 0; i < DM_HASH_SIZE; i++)
                 INIT_HLIST_HEAD(tm->buckets + i);
 
+        prefetch_init(&tm->prefetches);
+
         return tm;
 }
 
@@ -268,8 +329,14 @@ int dm_tm_read_lock(struct dm_transaction_manager *tm, dm_block_t b,
                     struct dm_block_validator *v,
                     struct dm_block **blk)
 {
-        if (tm->is_clone)
-                return dm_bm_read_try_lock(tm->real->bm, b, v, blk);
+        if (tm->is_clone) {
+                int r = dm_bm_read_try_lock(tm->real->bm, b, v, blk);
+
+                if (r == -EWOULDBLOCK)
+                        prefetch_add(&tm->real->prefetches, b);
+
+                return r;
+        }
 
         return dm_bm_read_lock(tm->bm, b, v, blk);
 }
@@ -317,6 +384,12 @@ struct dm_block_manager *dm_tm_get_bm(struct dm_transaction_manager *tm)
         return tm->bm;
 }
 
+void dm_tm_issue_prefetches(struct dm_transaction_manager *tm)
+{
+        prefetch_issue(&tm->prefetches, tm->bm);
+}
+EXPORT_SYMBOL_GPL(dm_tm_issue_prefetches);
+
 /*----------------------------------------------------------------*/
 
 static int dm_tm_create_internal(struct dm_block_manager *bm,
diff --git a/drivers/md/persistent-data/dm-transaction-manager.h b/drivers/md/persistent-data/dm-transaction-manager.h
index 2772ed2a781a..2e0d4d66fb1b 100644
--- a/drivers/md/persistent-data/dm-transaction-manager.h
+++ b/drivers/md/persistent-data/dm-transaction-manager.h
@@ -109,6 +109,13 @@ int dm_tm_ref(struct dm_transaction_manager *tm, dm_block_t b,
 struct dm_block_manager *dm_tm_get_bm(struct dm_transaction_manager *tm);
 
 /*
+ * If you're using a non-blocking clone the tm will build up a list of
+ * requested blocks that weren't in core.  This call will request those
+ * blocks to be prefetched.
+ */
+void dm_tm_issue_prefetches(struct dm_transaction_manager *tm);
+
+/*
  * A little utility that ties the knot by producing a transaction manager
  * that has a space map managed by the transaction manager...
  *