Patch "dm space maps: don't reset space map allocation cursor when committing" has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

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

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     dm-space-maps-don-t-reset-space-map-allocation-curso.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 900be0b8c7416fdd0739ec4a57422d99f6976ce0
Author: Joe Thornber <ejt@xxxxxxxxxx>
Date:   Tue Apr 13 09:03:49 2021 +0100

    dm space maps: don't reset space map allocation cursor when committing
    
    [ Upstream commit 5faafc77f7de69147d1e818026b9a0cbf036a7b2 ]
    
    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@xxxxxxxxxx>
    Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/md/persistent-data/dm-space-map-disk.c b/drivers/md/persistent-data/dm-space-map-disk.c
index bf4c5e2ccb6f..e0acae7a3815 100644
--- 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;
 
@@ -199,7 +207,6 @@ 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;
 
 	r = sm_disk_get_nr_free(sm, &nr_free);
diff --git a/drivers/md/persistent-data/dm-space-map-metadata.c b/drivers/md/persistent-data/dm-space-map-metadata.c
index 9e3c64ec2026..da439ac85796 100644
--- 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;