[PATCH 3.16 115/328] dm cache metadata: save in-core policy_hint_size to on-disk superblock

From: Ben Hutchings
Date: Sun Dec 09 2018 - 17:11:49 EST

3.16.62-rc1 review patch. If anyone has any objections, please let me know.


From: Mike Snitzer <snitzer@xxxxxxxxxx>

commit fd2fa95416188a767a63979296fa3e169a9ef5ec upstream.

policy_hint_size starts as 0 during __write_initial_superblock(). It
isn't until the policy is loaded that policy_hint_size is set in-core
(cmd->policy_hint_size). But it never got recorded in the on-disk
superblock because __commit_transaction() didn't deal with transfering
the in-core cmd->policy_hint_size to the on-disk superblock.

The in-core cmd->policy_hint_size gets initialized by metadata_open()'s
__begin_transaction_flags() which re-reads all superblock fields.
Because the superblock's policy_hint_size was never properly stored, when
the cache was created, hints_array_available() would always return false
when re-activating a previously created cache. This means
__load_mappings() always considered the hints invalid and never made use
of the hints (these hints served to optimize).

Another detremental side-effect of this oversight is the cache_check
utility would fail with: "invalid hint width: 0"

Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
drivers/md/dm-cache-metadata.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/md/dm-cache-metadata.c
+++ b/drivers/md/dm-cache-metadata.c
@@ -324,7 +324,7 @@ static int __write_initial_superblock(st
disk_super->version = cpu_to_le32(MAX_CACHE_VERSION);
memset(disk_super->policy_name, 0, sizeof(disk_super->policy_name));
memset(disk_super->policy_version, 0, sizeof(disk_super->policy_version));
- disk_super->policy_hint_size = 0;
+ disk_super->policy_hint_size = cpu_to_le32(0);

__copy_sm_root(cmd, disk_super);

@@ -635,6 +635,7 @@ static int __commit_transaction(struct d
disk_super->policy_version[0] = cpu_to_le32(cmd->policy_version[0]);
disk_super->policy_version[1] = cpu_to_le32(cmd->policy_version[1]);
disk_super->policy_version[2] = cpu_to_le32(cmd->policy_version[2]);
+ disk_super->policy_hint_size = cpu_to_le32(cmd->policy_hint_size);

disk_super->read_hits = cpu_to_le32(cmd->stats.read_hits);
disk_super->read_misses = cpu_to_le32(cmd->stats.read_misses);