Commit b1e09178 authored by John Garry's avatar John Garry Committed by Darrick J. Wong
Browse files

xfs: commit CoW-based atomic writes atomically 



When completing a CoW-based write, each extent range mapping update is
covered by a separate transaction.

For a CoW-based atomic write, all mappings must be changed at once, so
change to use a single transaction.

Note that there is a limit on the amount of log intent items which can be
fit into a single transaction, but this is being ignored for now since
the count of items for a typical atomic write would be much less than is
typically supported. A typical atomic write would be expected to be 64KB
or less, which means only 16 possible extents unmaps, which is quite
small.

Reviewed-by: default avatarDarrick J. Wong <djwong@kernel.org>
[djwong: add tr_atomic_ioend]
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarDarrick J. Wong <djwong@kernel.org>
Signed-off-by: default avatarJohn Garry <john.g.garry@oracle.com>
parent 11ab3190

fs/xfs/libxfs/xfs_log_rlimit.c

+4 −0
Original line number Diff line number Diff line
@@ -91,6 +91,7 @@ xfs_log_calc_trans_resv_for_minlogblocks( 
	 */

	if (xfs_want_minlogsize_fixes(&mp->m_sb)) {

		xfs_trans_resv_calc(mp, resv);

		resv->tr_atomic_ioend = M_RES(mp)->tr_atomic_ioend;

		return;

	}
@@ -107,6 +108,9 @@ xfs_log_calc_trans_resv_for_minlogblocks( 


	xfs_trans_resv_calc(mp, resv);



	/* Copy the dynamic transaction reservation types from the running fs */

	resv->tr_atomic_ioend = M_RES(mp)->tr_atomic_ioend;



	if (xfs_has_reflink(mp)) {

		/*

		 * In the early days of reflink, typical log operation counts

fs/xfs/libxfs/xfs_trans_resv.c

+15 −0
Original line number Diff line number Diff line
@@ -1284,6 +1284,15 @@ xfs_calc_namespace_reservations( 
	resp->tr_mkdir.tr_logflags |= XFS_TRANS_PERM_LOG_RES;

}



STATIC void

xfs_calc_default_atomic_ioend_reservation(

	struct xfs_mount	*mp,

	struct xfs_trans_resv	*resp)

{

	/* Pick a default that will scale reasonably for the log size. */

	resp->tr_atomic_ioend = resp->tr_itruncate;

}



void

xfs_trans_resv_calc(

	struct xfs_mount	*mp,
@@ -1378,4 +1387,10 @@ xfs_trans_resv_calc( 
	resp->tr_itruncate.tr_logcount += logcount_adj;

	resp->tr_write.tr_logcount += logcount_adj;

	resp->tr_qm_dqalloc.tr_logcount += logcount_adj;



	/*

	 * Now that we've finished computing the static reservations, we can

	 * compute the dynamic reservation for atomic writes.

	 */

	xfs_calc_default_atomic_ioend_reservation(mp, resp);

}

fs/xfs/libxfs/xfs_trans_resv.h

+1 −0
Original line number Diff line number Diff line
@@ -48,6 +48,7 @@ struct xfs_trans_resv { 
	struct xfs_trans_res	tr_qm_dqalloc;	/* allocate quota on disk */

	struct xfs_trans_res	tr_sb;		/* modify superblock */

	struct xfs_trans_res	tr_fsyncts;	/* update timestamps on fsync */

	struct xfs_trans_res	tr_atomic_ioend; /* untorn write completion */

};



/* shorthand way of accessing reservation structure */

fs/xfs/xfs_file.c

+4 −1
Original line number Diff line number Diff line
@@ -576,6 +576,9 @@ xfs_dio_write_end_io( 
	nofs_flag = memalloc_nofs_save();



	if (flags & IOMAP_DIO_COW) {

		if (iocb->ki_flags & IOCB_ATOMIC)

			error = xfs_reflink_end_atomic_cow(ip, offset, size);

		else

			error = xfs_reflink_end_cow(ip, offset, size);

		if (error)

			goto out;

fs/xfs/xfs_reflink.c

+56 −0
Original line number Diff line number Diff line
@@ -984,6 +984,62 @@ xfs_reflink_end_cow( 
	return error;

}



/*

 * Fully remap all of the file's data fork at once, which is the critical part

 * in achieving atomic behaviour.

 * The regular CoW end path does not use function as to keep the block

 * reservation per transaction as low as possible.

 */

int

xfs_reflink_end_atomic_cow(

	struct xfs_inode		*ip,

	xfs_off_t			offset,

	xfs_off_t			count)

{

	xfs_fileoff_t			offset_fsb;

	xfs_fileoff_t			end_fsb;

	int				error = 0;

	struct xfs_mount		*mp = ip->i_mount;

	struct xfs_trans		*tp;

	unsigned int			resblks;



	trace_xfs_reflink_end_cow(ip, offset, count);



	offset_fsb = XFS_B_TO_FSBT(mp, offset);

	end_fsb = XFS_B_TO_FSB(mp, offset + count);



	/*

	 * Each remapping operation could cause a btree split, so in the worst

	 * case that's one for each block.

	 */

	resblks = (end_fsb - offset_fsb) *

			XFS_NEXTENTADD_SPACE_RES(mp, 1, XFS_DATA_FORK);



	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_atomic_ioend, resblks, 0,

			XFS_TRANS_RESERVE, &tp);

	if (error)

		return error;



	xfs_ilock(ip, XFS_ILOCK_EXCL);

	xfs_trans_ijoin(tp, ip, 0);



	while (end_fsb > offset_fsb && !error) {

		error = xfs_reflink_end_cow_extent_locked(tp, ip, &offset_fsb,

				end_fsb);

	}

	if (error) {

		trace_xfs_reflink_end_cow_error(ip, error, _RET_IP_);

		goto out_cancel;

	}

	error = xfs_trans_commit(tp);

	xfs_iunlock(ip, XFS_ILOCK_EXCL);

	return error;

out_cancel:

	xfs_trans_cancel(tp);

	xfs_iunlock(ip, XFS_ILOCK_EXCL);

	return error;

}



/*

 * Free all CoW staging blocks that are still referenced by the ondisk refcount

 * metadata.  The ondisk metadata does not track which inode created the