delalloc-space.c | Explore in Territory

// SPDX-License-Identifier: GPL-2.0

#include "messages.h"
#include "ctree.h"
#include "delalloc-space.h"
#include "block-rsv.h"
#include "btrfs_inode.h"
#include "space-info.h"
#include "qgroup.h"
#include "fs.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 (current 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(const struct btrfs_inode *inode, u64 bytes)
{ … }

int btrfs_check_data_free_space(struct btrfs_inode *inode,
				struct extent_changeset **reserved, u64 start,
				u64 len, bool noflush)
{ … }

/*
 * 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 btrfs_fs_info *fs_info,
					    u64 len)
{ … }

/*
 * 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 btrfs_inode *inode,
			struct extent_changeset *reserved, u64 start, u64 len)
{ … }

/*
 * Release any excessive reservations for an inode.
 *
 * @inode:       the inode we need to release from
 * @qgroup_free: free or convert qgroup meta. Unlike normal operation, qgroup
 *               meta reservation needs to know if we are freeing qgroup
 *               reservation or just converting it into per-trans.  Normally
 *               @qgroup_free is true for error handling, and false for normal
 *               release.
 *
 * This is the same as btrfs_block_rsv_release, except that it handles the
 * tracepoint for the reservation.
 */
static void btrfs_inode_rsv_release(struct btrfs_inode *inode, bool qgroup_free)
{ … }

static void btrfs_calculate_inode_block_rsv_size(struct btrfs_fs_info *fs_info,
						 struct btrfs_inode *inode)
{ … }

static void calc_inode_reservations(struct btrfs_inode *inode,
				    u64 num_bytes, u64 disk_num_bytes,
				    u64 *meta_reserve, u64 *qgroup_reserve)
{ … }

int btrfs_delalloc_reserve_metadata(struct btrfs_inode *inode, u64 num_bytes,
				    u64 disk_num_bytes, bool noflush)
{ … }

/*
 * Release a metadata reservation for an inode.
 *
 * @inode:        the inode to release the reservation for.
 * @num_bytes:    the number of bytes we are releasing.
 * @qgroup_free:  free qgroup reservation or convert it to per-trans reservation
 *
 * This will release the metadata reservation for an inode.  This can be called
 * once we complete IO for a given set of bytes to release their metadata
 * reservations, or on error for the same reason.
 */
void btrfs_delalloc_release_metadata(struct btrfs_inode *inode, u64 num_bytes,
				     bool qgroup_free)
{ … }

/*
 * Release our outstanding_extents for an inode.
 *
 * @inode:      the inode to balance the reservation for.
 * @num_bytes:  the number of bytes we originally reserved with
 *
 * When we reserve space we increase outstanding_extents for the extents we may
 * add.  Once we've set the range as delalloc or created our ordered extents we
 * have outstanding_extents to track the real usage, so we use this to free our
 * temporarily tracked outstanding_extents.  This _must_ be used in conjunction
 * with btrfs_delalloc_reserve_metadata.
 */
void btrfs_delalloc_release_extents(struct btrfs_inode *inode, u64 num_bytes)
{ … }

/*
 * Reserve data and metadata space for delalloc
 *
 * @inode:     inode we're writing to
 * @start:     start range we are writing to
 * @len:       how long the range we are writing to
 * @reserved:  mandatory parameter, record actually reserved qgroup ranges of
 * 	       current reservation.
 *
 * This will do the following things
 *
 * - reserve space in data space info for num bytes and reserve precious
 *   corresponding qgroup space
 *   (Done in check_data_free_space)
 *
 * - reserve space for metadata space, based on the number of outstanding
 *   extents and how much csums will be needed also reserve metadata space in a
 *   per root over-reserve method.
 * - add to the inodes->delalloc_bytes
 * - add it to the fs_info's delalloc inodes list.
 *   (Above 3 all done in delalloc_reserve_metadata)
 *
 * Return 0 for success
 * Return <0 for error(-ENOSPC or -EDQUOT)
 */
int btrfs_delalloc_reserve_space(struct btrfs_inode *inode,
			struct extent_changeset **reserved, u64 start, u64 len)
{ … }

/*
 * Release data and metadata space for delalloc
 *
 * @inode:       inode we're releasing space for
 * @reserved:    list of changed/reserved ranges
 * @start:       start position of the space already reserved
 * @len:         length of the space already reserved
 * @qgroup_free: should qgroup reserved-space also be freed
 *
 * Release the metadata space that was not used and will decrement
 * ->delalloc_bytes and remove it from the fs_info->delalloc_inodes list if
 * there are no delalloc bytes left.  Also it will handle the qgroup reserved
 * space.
 */
void btrfs_delalloc_release_space(struct btrfs_inode *inode,
				  struct extent_changeset *reserved,
				  u64 start, u64 len, bool qgroup_free)
{ … }
linux/fs/btrfs/delalloc-space.c
