path: root/fs/btrfs/delalloc-space.c

// SPDX-License-Identifier: GPL-2.0

#include "ctree.h"
#include "delalloc-space.h"
#include "block-rsv.h"
#include "btrfs_inode.h"
#include "space-info.h"
#include "transaction.h"
#include "qgroup.h"
#include "block-group.h"

/*
 * HOW DOES THIS WORK
 *
 * There are two stages to data reservations, one for data and one for metadata
 * to handle the new extents and checksums generated by writing data.
 *
 *
 * DATA RESERVATION
 *   The general flow of the data reservation is as follows
 *
 *   -> Reserve
 *     We call into btrfs_reserve_data_bytes() for the user request bytes that
 *     they wish to write.  We make this reservation and add it to
 *     space_info->bytes_may_use.  We set EXTENT_DELALLOC on the inode io_tree
 *     for the range and carry on if this is buffered, or follow up trying to
 *     make a real allocation if we are pre-allocating or doing O_DIRECT.
 *
 *   -> Use
 *     At writepages()/prealloc/O_DIRECT time we will call into
 *     btrfs_reserve_extent() for some part or all of this range of bytes.  We
 *     will make the allocation and subtract space_info->bytes_may_use by the
 *     original requested length and increase the space_info->bytes_reserved by
 *     the allocated length.  This distinction is important because compression
 *     may allocate a smaller on disk extent than we previously reserved.
 *
 *   -> Allocation
 *     finish_ordered_io() will insert the new file extent item for this range,
 *     and then add a delayed ref update for the extent tree.  Once that delayed
 *     ref is written the extent size is subtracted from
 *     space_info->bytes_reserved and added to space_info->bytes_used.
 *
 *   Error handling
 *
 *   -> By the reservation maker
 *     This is the simplest case, we haven't completed our operation and we know
 *     how much we reserved, we can simply call
 *     btrfs_free_reserved_data_space*() and it will be removed from
 *     space_info->bytes_may_use.
 *
 *   -> After the reservation has been made, but before cow_file_range()
 *     This is specifically for the delalloc case.  You must clear
 *     EXTENT_DELALLOC with the EXTENT_CLEAR_DATA_RESV bit, and the range will
 *     be subtracted from space_info->bytes_may_use.
 *
 * METADATA RESERVATION
 *   The general metadata reservation lifetimes are discussed elsewhere, this
 *   will just focus on how it is used for delalloc space.
 *
 *   We keep track of two things on a per inode bases
 *
 *   ->outstanding_extents
 *     This is the number of file extent items we'll need to handle all of the
 *     outstanding DELALLOC space we have in this inode.  We limit the maximum
 *     size of an extent, so a large contiguous dirty area may require more than
 *     one outstanding_extent, which is why count_max_extents() is used to
 *     determine how many outstanding_extents get added.
 *
 *   ->csum_bytes
 *     This is essentially how many dirty bytes we have for this inode, so we
 *     can calculate the number of checksum items we would have to add in order
 *     to checksum our outstanding data.
 *
 *   We keep a per-inode block_rsv in order to make it easier to keep track of
 *   our reservation.  We use btrfs_calculate_inode_block_rsv_size() to
 *   calculate the current theoretical maximum reservation we would need for the
 *   metadata for this inode.  We call this and then adjust our reservation as
 *   necessary, either by attempting to reserve more space, or freeing up excess
 *   space.
 *
 * OUTSTANDING_EXTENTS HANDLING
 *
 *  ->outstanding_extents is used for keeping track of how many extents we will
 *  need to use for this inode, and it will fluctuate depending on where you are
 *  in the life cycle of the dirty data.  Consider the following normal case for
 *  a completely clean inode, with a num_bytes < our maximum allowed extent size
 *
 *  -> reserve
 *    ->outstanding_extents += 1 (current value is 1)
 *
 *  -> set_delalloc
 *    ->outstanding_extents += 1 (currrent value is 2)
 *
 *  -> btrfs_delalloc_release_extents()
 *    ->outstanding_extents -= 1 (current value is 1)
 *
 *    We must call this once we are done, as we hold our reservation for the
 *    duration of our operation, and then assume set_delalloc will update the
 *    counter appropriately.
 *
 *  -> add ordered extent
 *    ->outstanding_extents += 1 (current value is 2)
 *
 *  -> btrfs_clear_delalloc_extent
 *    ->outstanding_extents -= 1 (current value is 1)
 *
 *  -> finish_ordered_io/btrfs_remove_ordered_extent
 *    ->outstanding_extents -= 1 (current value is 0)
 *
 *  Each stage is responsible for their own accounting of the extent, thus
 *  making error handling and cleanup easier.
 */

int btrfs_alloc_data_chunk_ondemand(struct btrfs_inode *inode, u64 bytes)
{
	struct btrfs_root *root = inode->root;
	struct btrfs_fs_info *fs_info = root->fs_info;
	struct btrfs_space_info *data_sinfo = fs_info->data_sinfo;
	u64 used;
	int ret = 0;
	int need_commit = 2;
	int have_pinned_space;

	/* Make sure bytes are sectorsize aligned */
	bytes = ALIGN(bytes, fs_info->sectorsize);

	if (btrfs_is_free_space_inode(inode)) {
		need_commit = 0;
		ASSERT(current->journal_info);
	}

again:
	/* Make sure we have enough space to handle the data first */
	spin_lock(&data_sinfo->lock);
	used = btrfs_space_info_used(data_sinfo, true);

	if (used + bytes > data_sinfo->total_bytes) {
		struct btrfs_trans_handle *trans;

		/*
		 * If we don't have enough free bytes in this space then we need
		 * to alloc a new chunk.
		 */
		if (!data_sinfo->full) {
			u64 alloc_target;

			data_sinfo->force_alloc = CHUNK_ALLOC_FORCE;
			spin_unlock(&data_sinfo->lock);

			alloc_target = btrfs_data_alloc_profile(fs_info);
			/*
			 * It is ugly that we don't call nolock join
			 * transaction for the free space inode case here.
			 * But it is safe because we only do the data space
			 * reservation for the free space cache in the
			 * transaction context, the common join transaction
			 * just increase the counter of the current transaction
			 * handler, doesn't try to acquire the trans_lock of
			 * the fs.
			 */
			trans = btrfs_join_transaction(root);
			if (IS_ERR(trans))
				return PTR_ERR(trans);

			ret = btrfs_chunk_alloc(trans, alloc_target,
						CHUNK_ALLOC_NO_FORCE);
			btrfs_end_transaction(trans);
			if (ret < 0) {
				if (ret != -ENOSPC)
					return ret;
				else {
					have_pinned_space = 1;
					goto commit_trans;
				}
			}

			goto again;
		}

		/*
		 * If we don't have enough pinned space to deal with this
		 * allocation, and no removed chunk in current transaction,
		 * don't bother committing the transaction.
		 */
		have_pinned_space = __percpu_counter_compare(
			&data_sinfo->total_bytes_pinned,
			used + bytes - data_sinfo->total_bytes,
			BTRFS_TOTAL_BYTES_PINNED_BATCH);
		spin_unlock(&data_sinfo->lock);

		/* Commit the current transaction and try again */
commit_trans:
		if (need_commit) {
			need_commit--;

			if (need_commit > 0) {
				btrfs_start_delalloc_roots(fs_info, -1);
				btrfs_wait_ordered_roots(fs_info, U64_MAX, 0,
							 (u64)-1);
			}

			trans = btrfs_join_transaction(root);
			if (IS_ERR(trans))
				return PTR_ERR(trans);
			if (have_pinned_space >= 0 ||
			    test_bit(BTRFS_TRANS_HAVE_FREE_BGS,
				     &trans->transaction->flags) ||
			    need_commit > 0) {
				ret = btrfs_commit_transaction(trans);
				if (ret)
					return ret;
				/*
				 * The cleaner kthread might still be doing iput
				 * operations. Wait for it to finish so that
				 * more space is released.  We don't need to
				 * explicitly run the delayed iputs here because
				 * the commit_transaction would have woken up
				 * the cleaner.
				 */
				ret = btrfs_wait_on_delayed_iputs(fs_info);
				if (ret)
					return ret;
				goto again;
			} else {
				btrfs_end_transaction(trans);
			}
		}

		trace_btrfs_space_reservation(fs_info,
					      "space_info:enospc",
					      data_sinfo->flags, bytes, 1);
		return -ENOSPC;
	}
	btrfs_space_info_update_bytes_may_use(fs_info, data_sinfo, bytes);
	spin_unlock(&data_sinfo->lock);

	return 0;
}

int btrfs_check_data_free_space(struct inode *inode,
			struct extent_changeset **reserved, u64 start, u64 len)
{
	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
	int ret;

	/* align the range */
	len = round_up(start + len, fs_info->sectorsize) -
	      round_down(start, fs_info->sectorsize);
	start = round_down(start, fs_info->sectorsize);

	ret = btrfs_alloc_data_chunk_ondemand(BTRFS_I(inode), len);
	if (ret < 0)
		return ret;

	/* Use new btrfs_qgroup_reserve_data to reserve precious data space. */
	ret = btrfs_qgroup_reserve_data(inode, reserved, start, len);
	if (ret < 0)
		btrfs_free_reserved_data_space_noquota(inode, len);
	else
		ret = 0;
	return ret;
}

/*
 * Called if we need to clear a data reservation for this inode
 * Normally in a error case.
 *
 * This one will *NOT* use accurate qgroup reserved space API, just for case
 * which we can't sleep and is sure it won't affect qgroup reserved space.
 * Like clear_bit_hook().
 */
void btrfs_free_reserved_data_space_noquota(struct inode *inode,
					    u64 len)
{
	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
	struct btrfs_space_info *data_sinfo;

	ASSERT(IS_ALIGNED(len, fs_info->sectorsize));

	data_sinfo = fs_info->data_sinfo;
	spin_lock(&data_sinfo->lock);
	btrfs_space_info_update_bytes_may_use(fs_info, data_sinfo, -len);
	spin_unlock(&data_sinfo->lock);
}

/*
 * Called if we need to clear a data reservation for this inode
 * Normally in a error case.
 *
 * This one will handle the per-inode data rsv map for accurate reserved
 * space framework.
 */
void btrfs_free_reserved_data_space(struct inode *inode,
			struct extent_changeset *reserved, u64 start, u64 len)
{
	struct btrfs_root *root = BTRFS_I(inode)->root;

	/* Make sure the range is aligned to sectorsize */
	len = round_up(start + len, root->fs_info->sectorsize) -
	      round_down(start, root->fs_info->sectorsize);
	start = round_down(start, root->fs_info->sectorsize);

	btrfs_free_reserved_data_space_noquota(inode, len);
	btrfs_qgroup_free_data(BTRFS_I(inode), reserved, start