dm space maps: don't reset space map allocation cursor when committing

Current commit code resets the place where the search for free blocks
will begin back to the start of the metadata device.  There are a couple
of repercussions to this:

- The first allocation after the commit is likely to take longer than
  normal as it searches for a free block in an area that is likely to
  have very few free blocks (if any).

- Any free blocks it finds will have been recently freed.  Reusing them
  means we have fewer old copies of the metadata to aid recovery from
  hardware error.

Fix these issues by leaving the cursor alone, only resetting when the
search hits the end of the metadata device.

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

diff --git a/drivers/md/persistent-data/dm-space-map-disk.c b/drivers/md/persistent-data/dm-space-map-disk.c
index 61f56909e00bebd7862976a07b71b268e17fc6b0..4f8069bb04816af475651c35bc470505dad3b3ff 100644 (file)
--- a/drivers/md/persistent-data/dm-space-map-disk.c
+++ b/drivers/md/persistent-data/dm-space-map-disk.c
@@ -171,6 +171,14 @@ static int sm_disk_new_block(struct dm_space_map *sm, dm_block_t *b)
         * Any block we allocate has to be free in both the old and current ll.
         */
        r = sm_ll_find_common_free_block(&smd->old_ll, &smd->ll, smd->begin, smd->ll.nr_blocks, b);
+       if (r == -ENOSPC) {
+               /*
+                * There's no free block between smd->begin and the end of the metadata device.
+                * We search before smd->begin in case something has been freed.
+                */
+               r = sm_ll_find_common_free_block(&smd->old_ll, &smd->ll, 0, smd->begin, b);
+       }
+
        if (r)
                return r;
 
@@ -194,7 +202,6 @@ static int sm_disk_commit(struct dm_space_map *sm)
                return r;
 
        memcpy(&smd->old_ll, &smd->ll, sizeof(smd->old_ll));
-       smd->begin = 0;
        smd->nr_allocated_this_transaction = 0;
 
        return 0;

diff --git a/drivers/md/persistent-data/dm-space-map-metadata.c b/drivers/md/persistent-data/dm-space-map-metadata.c
index 9e3c64ec2026fa66b3b1a02adcd5c3b0085f1318..da439ac85796374e1c4582c02b4a884df38564c4 100644 (file)
--- a/drivers/md/persistent-data/dm-space-map-metadata.c
+++ b/drivers/md/persistent-data/dm-space-map-metadata.c
@@ -452,6 +452,14 @@ static int sm_metadata_new_block_(struct dm_space_map *sm, dm_block_t *b)
         * Any block we allocate has to be free in both the old and current ll.
         */
        r = sm_ll_find_common_free_block(&smm->old_ll, &smm->ll, smm->begin, smm->ll.nr_blocks, b);
+       if (r == -ENOSPC) {
+               /*
+                * There's no free block between smm->begin and the end of the metadata device.
+                * We search before smm->begin in case something has been freed.
+                */
+               r = sm_ll_find_common_free_block(&smm->old_ll, &smm->ll, 0, smm->begin, b);
+       }
+
        if (r)
                return r;
 
@@ -503,7 +511,6 @@ static int sm_metadata_commit(struct dm_space_map *sm)
                return r;
 
        memcpy(&smm->old_ll, &smm->ll, sizeof(smm->old_ll));
-       smm->begin = 0;
        smm->allocated_this_transaction = 0;
 
        return 0;