Re: [PATCH RFC 02/10] xfs: Refactor xfs_reflink_end_cow_extent()

Darrick J. Wong
2025-02-05T19:50:51Z

On Tue, Feb 04, 2025 at 12:01:19PM +0000, John Garry wrote:
> Refactor xfs_reflink_end_cow_extent() into separate parts which process
> the CoW range and commit the transaction.
>
> This refactoring will be used in future for when it is required to commit
> a range of extents as a single transaction, similar to how it was done
> pre-commit d6f215f359637.
>
> Signed-off-by: John Garry <john.g.garry@oracle.com>
> ---
> fs/xfs/xfs_reflink.c | 79 +++++++++++++++++++++++++++-----------------
> 1 file changed, 48 insertions(+), 31 deletions(-)
>
> diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> index 59f7fc16eb80..580469668334 100644
> --- a/fs/xfs/xfs_reflink.c
> +++ b/fs/xfs/xfs_reflink.c
> @@ -786,35 +786,20 @@ xfs_reflink_update_quota(
> * requirements as low as possible.
> */
> STATIC int
> -xfs_reflink_end_cow_extent(
> +xfs_reflink_end_cow_extent_locked(
> struct xfs_inode *ip,
> xfs_fileoff_t *offset_fsb,
> - xfs_fileoff_t end_fsb)
> + xfs_fileoff_t end_fsb,
> + struct xfs_trans *tp,
> + bool *commit)

Transactions usually come before the inode in the parameter list.

You don't need to pass out a @commit flag -- if the function returns
nonzero then the caller has to cancel the transaction; otherwise it will
return zero and the caller should commit it. There's no penalty for
committing a non-dirty transaction.

--D

> {
> struct xfs_iext_cursor icur;
> struct xfs_bmbt_irec got, del, data;
> - struct xfs_mount *mp = ip->i_mount;
> - struct xfs_trans *tp;
> struct xfs_ifork *ifp = xfs_ifork_ptr(ip, XFS_COW_FORK);
> - unsigned int resblks;
> int nmaps;
> bool isrt = XFS_IS_REALTIME_INODE(ip);
> int error;
>
> - resblks = XFS_EXTENTADD_SPACE_RES(mp, XFS_DATA_FORK);
> - error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, resblks, 0,
> - XFS_TRANS_RESERVE, &tp);
> - if (error)
> - return error;
> -
> - /*
> - * Lock the inode. We have to ijoin without automatic unlock because
> - * the lead transaction is the refcountbt record deletion; the data
> - * fork update follows as a deferred log item.
> - */
> - xfs_ilock(ip, XFS_ILOCK_EXCL);
> - xfs_trans_ijoin(tp, ip, 0);
> -
> /*
> * In case of racing, overlapping AIO writes no COW extents might be
> * left by the time I/O completes for the loser of the race. In that
> @@ -823,7 +808,7 @@ xfs_reflink_end_cow_extent(
> if (!xfs_iext_lookup_extent(ip, ifp, *offset_fsb, &icur, &got) ||
> got.br_startoff >= end_fsb) {
> *offset_fsb = end_fsb;
> - goto out_cancel;
> + return 0;
> }
>
> /*
> @@ -837,7 +822,7 @@ xfs_reflink_end_cow_extent(
> if (!xfs_iext_next_extent(ifp, &icur, &got) ||
> got.br_startoff >= end_fsb) {
> *offset_fsb = end_fsb;
> - goto out_cancel;
> + return 0;
> }
> }
> del = got;
> @@ -846,14 +831,14 @@ xfs_reflink_end_cow_extent(
> error = xfs_iext_count_extend(tp, ip, XFS_DATA_FORK,
> XFS_IEXT_REFLINK_END_COW_CNT);
> if (error)
> - goto out_cancel;
> + return error;
>
> /* Grab the corresponding mapping in the data fork. */
> nmaps = 1;
> error = xfs_bmapi_read(ip, del.br_startoff, del.br_blockcount, &data,
> &nmaps, 0);
> if (error)
> - goto out_cancel;
> + return error;
>
> /* We can only remap the smaller of the two extent sizes. */
> data.br_blockcount = min(data.br_blockcount, del.br_blockcount);
> @@ -882,7 +867,7 @@ xfs_reflink_end_cow_extent(
> error = xfs_bunmapi(NULL, ip, data.br_startoff,
> data.br_blockcount, 0, 1, &done);
> if (error)
> - goto out_cancel;
> + return error;
> ASSERT(done);
> }
>
> @@ -899,17 +884,49 @@ xfs_reflink_end_cow_extent(
> /* Remove the mapping from the CoW fork. */
> xfs_bmap_del_extent_cow(ip, &icur, &got, &del);
>
> - error = xfs_trans_commit(tp);
> - xfs_iunlock(ip, XFS_ILOCK_EXCL);
> - if (error)
> - return error;
> -
> /* Update the caller about how much progress we made. */
> *offset_fsb = del.br_startoff + del.br_blockcount;
> + *commit = true;
> return 0;
> +}
>
> -out_cancel:
> - xfs_trans_cancel(tp);
> +
> +/*
> + * Remap part of the CoW fork into the data fork.
> + *
> + * We aim to remap the range starting at @offset_fsb and ending at @end_fsb
> + * into the data fork; this function will remap what it can (at the end of the
> + * range) and update @end_fsb appropriately. Each remap gets its own
> + * transaction because we can end up merging and splitting bmbt blocks for
> + * every remap operation and we'd like to keep the block reservation
> + * requirements as low as possible.
> + */
> +STATIC int
> +xfs_reflink_end_cow_extent(
> + struct xfs_inode *ip,
> + xfs_fileoff_t *offset_fsb,
> + xfs_fileoff_t end_fsb)
> +{
> + struct xfs_mount *mp = ip->i_mount;
> + struct xfs_trans *tp;
> + unsigned int resblks;
> + int error;
> + bool commit = false;
> +
> + resblks = XFS_EXTENTADD_SPACE_RES(mp, XFS_DATA_FORK);
> + error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, resblks, 0,
> + XFS_TRANS_RESERVE, &tp);
> + if (error)
> + return error;
> + xfs_ilock(ip, XFS_ILOCK_EXCL);
> + xfs_trans_ijoin(tp, ip, 0);
> +
> + error = xfs_reflink_end_cow_extent_locked(ip, offset_fsb,
> + end_fsb, tp, &commit);
> + if (commit)
> + error = xfs_trans_commit(tp);
> + else
> + xfs_trans_cancel(tp);
> xfs_iunlock(ip, XFS_ILOCK_EXCL);
> return error;
> }
> --
> 2.31.1
>
>