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>

diff --git a/drivers/md/persistent-data/dm-transaction-manager.c b/drivers/md/persistent-data/dm-transaction-manager.c
index 3bc30a0ae3d6084a2e08b356ac40c9082c6d5c62..9cb797d800cf8de36479130708a4a58e12e64a23 100644 (file)
--- 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 2772ed2a781a5de107e13d275f21b2ad1d98c7ea..2e0d4d66fb1bafe15d3d70e8d41635320cc36308 100644 (file)
--- a/drivers/md/persistent-data/dm-transaction-manager.h
+++ b/drivers/md/persistent-data/dm-transaction-manager.h
@@ -108,6 +108,13 @@ 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...