dm cache: speed up writing of the hint array

It's far quicker to always delete the hint array and recreate with
dm_array_new() because we avoid the copying caused by mutation.

Also simplifies the policy interface, replacing the walk_hints() with
the simpler get_hint().

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

1 files changed, 27 insertions, 53 deletions

diff --git a/drivers/md/dm-cache-metadata.c b/drivers/md/dm-cache-metadata.c
index 3970cda10080..a60f10a0ee0a 100644
--- a/drivers/md/dm-cache-metadata.c
+++ b/drivers/md/dm-cache-metadata.c
@@ -1368,10 +1368,24 @@ int dm_cache_get_metadata_dev_size(struct dm_cache_metadata *cmd,
 
 /*----------------------------------------------------------------*/
 
-static int begin_hints(struct dm_cache_metadata *cmd, struct dm_cache_policy *policy)
+static int get_hint(uint32_t index, void *value_le, void *context)
+{
+        uint32_t value;
+        struct dm_cache_policy *policy = context;
+
+        value = policy_get_hint(policy, to_cblock(index));
+        *((__le32 *) value_le) = cpu_to_le32(value);
+
+        return 0;
+}
+
+/*
+ * It's quicker to always delete the hint array, and recreate with
+ * dm_array_new().
+ */
+static int write_hints(struct dm_cache_metadata *cmd, struct dm_cache_policy *policy)
 {
         int r;
-        __le32 value;
         size_t hint_size;
         const char *policy_name = dm_cache_policy_get_name(policy);
         const unsigned *policy_version = dm_cache_policy_get_version(policy);
@@ -1380,63 +1394,23 @@ static int begin_hints(struct dm_cache_metadata *cmd, struct dm_cache_policy *po
             (strlen(policy_name) > sizeof(cmd->policy_name) - 1))
                 return -EINVAL;
 
-        if (!policy_unchanged(cmd, policy)) {
-                strncpy(cmd->policy_name, policy_name, sizeof(cmd->policy_name));
-                memcpy(cmd->policy_version, policy_version, sizeof(cmd->policy_version));
+        strncpy(cmd->policy_name, policy_name, sizeof(cmd->policy_name));
+        memcpy(cmd->policy_version, policy_version, sizeof(cmd->policy_version));
 
-                hint_size = dm_cache_policy_get_hint_size(policy);
-                if (!hint_size)
-                        return 0; /* short-circuit hints initialization */
-                cmd->policy_hint_size = hint_size;
+        hint_size = dm_cache_policy_get_hint_size(policy);
+        if (!hint_size)
+                return 0; /* short-circuit hints initialization */
+        cmd->policy_hint_size = hint_size;
 
-                if (cmd->hint_root) {
-                        r = dm_array_del(&cmd->hint_info, cmd->hint_root);
-                        if (r)
-                                return r;
-                }
-
-                r = dm_array_empty(&cmd->hint_info, &cmd->hint_root);
+        if (cmd->hint_root) {
+                r = dm_array_del(&cmd->hint_info, cmd->hint_root);
                 if (r)
                         return r;
-
-                value = cpu_to_le32(0);
-                __dm_bless_for_disk(&value);
-                r = dm_array_resize(&cmd->hint_info, cmd->hint_root, 0,
-                                    from_cblock(cmd->cache_blocks),
-                                    &value, &cmd->hint_root);
-                if (r)
-                        return r;
-        }
-
-        return 0;
-}
-
-static int save_hint(void *context, dm_cblock_t cblock, dm_oblock_t oblock, uint32_t hint)
-{
-        struct dm_cache_metadata *cmd = context;
-        __le32 value = cpu_to_le32(hint);
-        int r;
-
-        __dm_bless_for_disk(&value);
-
-        r = dm_array_set_value(&cmd->hint_info, cmd->hint_root,
-                               from_cblock(cblock), &value, &cmd->hint_root);
-        cmd->changed = true;
-
-        return r;
-}
-
-static int write_hints(struct dm_cache_metadata *cmd, struct dm_cache_policy *policy)
-{
-        int r;
-
-        r = begin_hints(cmd, policy);
-        if (r) {
-                DMERR("begin_hints failed");
-                return r;
         }
 
-        return policy_walk_mappings(policy, save_hint, cmd);
+        return dm_array_new(&cmd->hint_info, &cmd->hint_root,
+                            from_cblock(cmd->cache_blocks),
+                            get_hint, policy);
 }
 
 int dm_cache_write_hints(struct dm_cache_metadata *cmd, struct dm_cache_policy *policy)