btrfs: get rid of block group caching progress logic

struct btrfs_caching_ctl::progress and struct
btrfs_block_group::last_byte_to_unpin were previously needed to ensure
that unpin_extent_range() didn't return a range to the free space cache
before the caching thread had a chance to cache that range. However, the
commit "btrfs: fix space cache corruption and potential double
allocations" made it so that we always synchronously cache the block
group at the time that we pin the extent, so this machinery is no longer
necessary.

Reviewed-by: Filipe Manana <[e-mail]>
Signed-off-by: Omar Sandoval <[e-mail]>
Signed-off-by: David Sterba <[e-mail]>

fs/btrfs/block-group.c

···
 
 			if (need_resched() ||
 			    rwsem_is_contended(&fs_info->commit_root_sem)) {
-				if (wakeup)
-					caching_ctl->progress = last;
 				btrfs_release_path(path);
 				up_read(&fs_info->commit_root_sem);
 				mutex_unlock(&caching_ctl->mutex);
···
 			key.objectid = last;
 			key.offset = 0;
 			key.type = BTRFS_EXTENT_ITEM_KEY;
-
-			if (wakeup)
-				caching_ctl->progress = last;
 			btrfs_release_path(path);
 			goto next;
 		}
···
 
 	total_found += add_new_free_space(block_group, last,
 				block_group->start + block_group->length);
-	caching_ctl->progress = (u64)-1;
 
 out:
 	btrfs_free_path(path);
···
 	}
 #endif
 
-	caching_ctl->progress = (u64)-1;
-
 	up_read(&fs_info->commit_root_sem);
 	btrfs_free_excluded_extents(block_group);
 	mutex_unlock(&caching_ctl->mutex);
···
 	mutex_init(&caching_ctl->mutex);
 	init_waitqueue_head(&caching_ctl->wait);
 	caching_ctl->block_group = cache;
-	caching_ctl->progress = cache->start;
 	refcount_set(&caching_ctl->count, 2);
 	btrfs_init_work(&caching_ctl->work, caching_thread, NULL, NULL);
 
···
 		/* Should not have any excluded extents. Just in case, though. */
 		btrfs_free_excluded_extents(cache);
 	} else if (cache->length == cache->used) {
-		cache->last_byte_to_unpin = (u64)-1;
 		cache->cached = BTRFS_CACHE_FINISHED;
 		btrfs_free_excluded_extents(cache);
 	} else if (cache->used == 0) {
-		cache->last_byte_to_unpin = (u64)-1;
 		cache->cached = BTRFS_CACHE_FINISHED;
 		add_new_free_space(cache, cache->start,
 				   cache->start + cache->length);
···
 		/* Fill dummy cache as FULL */
 		bg->length = em->len;
 		bg->flags = map->type;
-		bg->last_byte_to_unpin = (u64)-1;
 		bg->cached = BTRFS_CACHE_FINISHED;
 		bg->used = em->len;
 		bg->flags = map->type;
···
 	set_free_space_tree_thresholds(cache);
 	cache->used = bytes_used;
 	cache->flags = type;
-	cache->last_byte_to_unpin = (u64)-1;
 	cache->cached = BTRFS_CACHE_FINISHED;
 	cache->global_root_id = calculate_global_root_id(fs_info, cache->start);
 

fs/btrfs/block-group.h

···
 	wait_queue_head_t wait;
 	struct btrfs_work work;
 	struct btrfs_block_group *block_group;
-	u64 progress;
 	refcount_t count;
 };
 
···
 	/* Cache tracking stuff */
 	int cached;
 	struct btrfs_caching_control *caching_ctl;
-	u64 last_byte_to_unpin;
 
 	struct btrfs_space_info *space_info;
 

fs/btrfs/extent-tree.c

···
 		len = cache->start + cache->length - start;
 		len = min(len, end + 1 - start);
 
-		down_read(&fs_info->commit_root_sem);
-		if (start < cache->last_byte_to_unpin && return_free_space) {
-			u64 add_len = min(len, cache->last_byte_to_unpin - start);
-
-			btrfs_add_free_space(cache, start, add_len);
-		}
-		up_read(&fs_info->commit_root_sem);
+		if (return_free_space)
+			btrfs_add_free_space(cache, start, len);
 
 		start += len;
 		total_unpinned += len;

fs/btrfs/free-space-tree.c

···
 		ASSERT(key.type == BTRFS_FREE_SPACE_BITMAP_KEY);
 		ASSERT(key.objectid < end && key.objectid + key.offset <= end);
 
-		caching_ctl->progress = key.objectid;
-
 		offset = key.objectid;
 		while (offset < key.objectid + key.offset) {
 			bit = free_space_test_bit(block_group, path, offset);
···
 		ret = -EIO;
 		goto out;
 	}
-
-	caching_ctl->progress = (u64)-1;
 
 	ret = 0;
 out:
···
 		ASSERT(key.type == BTRFS_FREE_SPACE_EXTENT_KEY);
 		ASSERT(key.objectid < end && key.objectid + key.offset <= end);
 
-		caching_ctl->progress = key.objectid;
-
 		total_found += add_new_free_space(block_group, key.objectid,
 						  key.objectid + key.offset);
 		if (total_found > CACHING_CTL_WAKE_UP) {
···
 		ret = -EIO;
 		goto out;
 	}
-
-	caching_ctl->progress = (u64)-1;
 
 	ret = 0;
 out:

fs/btrfs/transaction.c

···
 	struct btrfs_transaction *cur_trans = trans->transaction;
 	struct btrfs_fs_info *fs_info = trans->fs_info;
 	struct btrfs_root *root, *tmp;
-	struct btrfs_caching_control *caching_ctl, *next;
 
 	/*
 	 * At this point no one can be using this transaction to modify any tree
···
 	}
 	spin_unlock(&cur_trans->dropped_roots_lock);
 
-	/*
-	 * We have to update the last_byte_to_unpin under the commit_root_sem,
-	 * at the same time we swap out the commit roots.
-	 *
-	 * This is because we must have a real view of the last spot the caching
-	 * kthreads were while caching.  Consider the following views of the
-	 * extent tree for a block group
-	 *
-	 * commit root
-	 * +----+----+----+----+----+----+----+
-	 * |\\\\|    |\\\\|\\\\|    |\\\\|\\\\|
-	 * +----+----+----+----+----+----+----+
-	 * 0    1    2    3    4    5    6    7
-	 *
-	 * new commit root
-	 * +----+----+----+----+----+----+----+
-	 * |    |    |    |\\\\|    |    |\\\\|
-	 * +----+----+----+----+----+----+----+
-	 * 0    1    2    3    4    5    6    7
-	 *
-	 * If the cache_ctl->progress was at 3, then we are only allowed to
-	 * unpin [0,1) and [2,3], because the caching thread has already
-	 * processed those extents.  We are not allowed to unpin [5,6), because
-	 * the caching thread will re-start it's search from 3, and thus find
-	 * the hole from [4,6) to add to the free space cache.
-	 */
-	write_lock(&fs_info->block_group_cache_lock);
-	list_for_each_entry_safe(caching_ctl, next,
-				 &fs_info->caching_block_groups, list) {
-		struct btrfs_block_group *cache = caching_ctl->block_group;
-
-		if (btrfs_block_group_done(cache)) {
-			cache->last_byte_to_unpin = (u64)-1;
-			list_del_init(&caching_ctl->list);
-			btrfs_put_caching_control(caching_ctl);
-		} else {
-			cache->last_byte_to_unpin = caching_ctl->progress;
-		}
-	}
-	write_unlock(&fs_info->block_group_cache_lock);
 	up_write(&fs_info->commit_root_sem);
 }
 

fs/btrfs/zoned.c

···
 	free = cache->zone_capacity - cache->alloc_offset;
 
 	/* We only need ->free_space in ALLOC_SEQ block groups */
-	cache->last_byte_to_unpin = (u64)-1;
 	cache->cached = BTRFS_CACHE_FINISHED;
 	cache->free_space_ctl->free_space = free;
 	cache->zone_unusable = unusable;