[PATCH 05/15] btrfs: Handle pending/pinned chunks before blockgroup relocation during device shrink

Nikolay Borisov
2019-01-30T14:51:15Z

During device shrink pinned/pending chunks (i.e those which have been
deleted/created respectively, in the current transaction and haven't
touched disk) need to be accounted when doing device shrink. Presently
this happens after the main relocation loop in btrfs_shrink_device,
which could lead to making another go in the body of the function.

Since there is no hard requirement to perform pinned/pending chunks
handling after the relocation loop, move the code before it. This leads
to simplifying the code flow around - i.e no need to use 'goto again'.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
---
fs/btrfs/volumes.c | 54 ++++++++++++++++++----------------------------
1 file changed, 21 insertions(+), 33 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 4f645e1b5539..be91432697ab 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4712,15 +4712,15 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
int slot;
int failed = 0;
bool retried = false;
- bool checked_pending_chunks = false;
struct extent_buffer *l;
struct btrfs_key key;
struct btrfs_super_block *super_copy = fs_info->super_copy;
u64 old_total = btrfs_super_total_bytes(super_copy);
u64 old_size = btrfs_device_get_total_bytes(device);
u64 diff;
+ u64 start;

- new_size = round_down(new_size, fs_info->sectorsize);
+ start = new_size = round_down(new_size, fs_info->sectorsize);
diff = round_down(old_size - new_size, fs_info->sectorsize);

if (test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state))
@@ -4732,6 +4732,10 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)

path->reada = READA_BACK;

+ trans = btrfs_start_transaction(root, 0);
+ if (IS_ERR(trans))
+ return PTR_ERR(trans);
+
mutex_lock(&fs_info->chunk_mutex);

btrfs_device_set_total_bytes(device, new_size);
@@ -4739,7 +4743,21 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
device->fs_devices->total_rw_bytes -= diff;
atomic64_sub(diff, &fs_info->free_chunk_space);
}
- mutex_unlock(&fs_info->chunk_mutex);
+
+ /*
+ * Once the device's size has been set to the new size, ensure all
+ * in-memory chunks are synced to disk so that the loop below sees them
+ * and relocates them accordingly.
+ */
+ if (contains_pending_extent(trans->transaction, device, &start, diff)) {
+ mutex_unlock(&fs_info->chunk_mutex);
+ ret = btrfs_commit_transaction(trans);
+ if (ret)
+ goto done;
+ } else {
+ mutex_unlock(&fs_info->chunk_mutex);
+ btrfs_end_transaction(trans);
+ }

again:
key.objectid = device->devid;
@@ -4830,36 +4848,6 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
}

mutex_lock(&fs_info->chunk_mutex);
-
- /*
- * We checked in the above loop all device extents that were already in
- * the device tree. However before we have updated the device's
- * total_bytes to the new size, we might have had chunk allocations that
- * have not complete yet (new block groups attached to transaction
- * handles), and therefore their device extents were not yet in the
- * device tree and we missed them in the loop above. So if we have any
- * pending chunk using a device extent that overlaps the device range
- * that we can not use anymore, commit the current transaction and
- * repeat the search on the device tree - this way we guarantee we will
- * not have chunks using device extents that end beyond 'new_size'.
- */
- if (!checked_pending_chunks) {
- u64 start = new_size;
- u64 len = old_size - new_size;
-
- if (contains_pending_extent(trans->transaction, device,
- &start, len)) {
- mutex_unlock(&fs_info->chunk_mutex);
- checked_pending_chunks = true;
- failed = 0;
- retried = false;
- ret = btrfs_commit_transaction(trans);
- if (ret)
- goto done;
- goto again;
- }
- }
-
btrfs_device_set_disk_total_bytes(device, new_size);
if (list_empty(&device->post_commit_list))
list_add_tail(&device->post_commit_list,
--
2.17.1