On Mon, Dec 05, 2016 at 10:05:23PM +0100, Christoph Hellwig wrote:
> When we allocate COW fork blocks for direct I/O writes we currently first
> create a delayed allocation, and then convert it to a real allocation
> once we've got the delayed one.
>
> As there is no good reason for that this patch instead makes use call
> xfs_bmapi_write from the COW allocation path. The only interesting bits
> are a few tweaks the low-level allocator to allow for this, most notably
> the need to remove the call to xfs_bmap_extsize_align for the cowextsize
> in xfs_bmap_btalloc - for the existing convert case it's a no-op, but
> for the direct allocation case it would blow up our block reservation
> way beyond what we reserved for the transaction.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> fs/xfs/libxfs/xfs_bmap.c | 9 ++---
> fs/xfs/xfs_reflink.c | 101 ++++++++++++++++++++++++++++++++++-------------
> 2 files changed, 76 insertions(+), 34 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index 6f28814..a4a4327 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -2893,13 +2893,14 @@ xfs_bmap_add_extent_hole_real(
> ASSERT(!isnullstartblock(new->br_startblock));
> ASSERT(!bma->cur ||
> !(bma->cur->bc_private.b.flags & XFS_BTCUR_BPRV_WASDEL));
> - ASSERT(whichfork != XFS_COW_FORK);
>
> XFS_STATS_INC(mp, xs_add_exlist);
>
> state = 0;
> if (whichfork == XFS_ATTR_FORK)
> state |= BMAP_ATTRFORK;
> + if (whichfork == XFS_COW_FORK)
> + state |= BMAP_COWFORK;
>
> /*
> * Check and set flags if this segment has a left neighbor.
> @@ -3619,9 +3620,7 @@ xfs_bmap_btalloc(
> else if (mp->m_dalign)
> stripe_align = mp->m_dalign;
>
> - if (ap->flags & XFS_BMAPI_COWFORK)
> - align = xfs_get_cowextsz_hint(ap->ip);
> - else if (xfs_alloc_is_userdata(ap->datatype))
> + if (xfs_alloc_is_userdata(ap->datatype))
Doesn't this defeat the purpose (i.e., fragmentation avoidance via wider
allocations) of the cowextszhint for direct I/O? I think it would be
better to be consistent with the approach for traditional I/O + extsz
and incorporate the alignment into the reservation. Perhaps the hunk of
code that already does just that in xfs_iomap_write_direct() could be
converted to a small helper and reused..?
> align = xfs_get_extsz_hint(ap->ip);
> if (unlikely(align)) {
> error = xfs_bmap_extsize_align(mp, &ap->got, &ap->prev,
> @@ -4608,8 +4607,6 @@ xfs_bmapi_write(
> */
> if (flags & XFS_BMAPI_REMAP)
> ASSERT(inhole);
> - if (flags & XFS_BMAPI_COWFORK)
> - ASSERT(!inhole);
>
> /*
> * First, deal with the hole before the allocated space
> diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> index 88fd03c..0a077e80 100644
> --- a/fs/xfs/xfs_reflink.c
> +++ b/fs/xfs/xfs_reflink.c
> @@ -304,59 +304,104 @@ __xfs_reflink_allocate_cow(
> xfs_fileoff_t end_fsb)
> {
> struct xfs_mount *mp = ip->i_mount;
> - struct xfs_bmbt_irec imap;
> + struct xfs_bmbt_irec imap, got;
> struct xfs_defer_ops dfops;
> struct xfs_trans *tp;
> xfs_fsblock_t first_block;
> - int nimaps = 1, error;
> - bool shared;
> + int nimaps, error, lockmode;
> + bool shared, trimmed;
> + xfs_extlen_t resblks, align;
> + xfs_extnum_t idx;
>
> - xfs_defer_init(&dfops, &first_block);
> + align = xfs_eof_alignment(ip, xfs_get_cowextsz_hint(ip));
> + if (align)
> + end_fsb = roundup_64(end_fsb, align);
>
> - error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, 0, 0,
> - XFS_TRANS_RESERVE, &tp);
> + resblks = XFS_DIOSTRAT_SPACE_RES(mp, end_fsb - *offset_fsb);
> +
> + error = xfs_qm_dqattach(ip, 0);
This is already in the (only) caller.
Brian
> if (error)
> return error;
>
> - xfs_ilock(ip, XFS_ILOCK_EXCL);
> -
> - /* Read extent from the source file. */
> - nimaps = 1;
> - error = xfs_bmapi_read(ip, *offset_fsb, end_fsb - *offset_fsb,
> - &imap, &nimaps, 0);
> + error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, resblks, 0, 0, &tp);
> if (error)
> - goto out_unlock;
> - ASSERT(nimaps == 1);
> + return error;
>
> - error = xfs_reflink_reserve_cow(ip, &imap, &shared);
> - if (error)
> - goto out_trans_cancel;
> + lockmode = XFS_ILOCK_EXCL;
> + xfs_ilock(ip, lockmode);
>
> - if (!shared) {
> - *offset_fsb = imap.br_startoff + imap.br_blockcount;
> - goto out_trans_cancel;
> + /*
> + * Even if the extent is not shared we might have a preallocation for
> + * it in the COW fork. If so use it.
> + */
> + if (xfs_iext_lookup_extent(ip, ip->i_cowfp, *offset_fsb, &idx, &got) &&
> + got.br_startoff <= *offset_fsb) {
> + /* If we have a real allocation in the COW fork we're done. */
> + if (!isnullstartblock(got.br_startblock)) {
> + xfs_trim_extent(&got, *offset_fsb,
> + end_fsb - *offset_fsb);
> + *offset_fsb = got.br_startoff + got.br_blockcount;
> + goto out_trans_cancel;
> + }
> + } else {
> + nimaps = 1;
> + error = xfs_bmapi_read(ip, *offset_fsb, end_fsb - *offset_fsb,
> + &imap, &nimaps, 0);
> + if (error)
> + goto out_trans_cancel;
> + ASSERT(nimaps == 1);
> +
> + /* Trim the mapping to the nearest shared extent boundary. */
> + error = xfs_reflink_trim_around_shared(ip, &imap, &shared,
> + &trimmed);
> + if (error)
> + goto out_trans_cancel;
> +
> + if (!shared) {
> + *offset_fsb = imap.br_startoff + imap.br_blockcount;
> + goto out_trans_cancel;
> + }
> +
> + *offset_fsb = imap.br_startoff;
> + end_fsb = imap.br_startoff + imap.br_blockcount;
> + if (align)
> + end_fsb = roundup_64(end_fsb, align);
> }
>
> - xfs_trans_ijoin(tp, ip, 0);
> - error = xfs_bmapi_write(tp, ip, imap.br_startoff, imap.br_blockcount,
> - XFS_BMAPI_COWFORK, &first_block,
> - XFS_EXTENTADD_SPACE_RES(mp, XFS_DATA_FORK),
> - &imap, &nimaps, &dfops);
> + error = xfs_trans_reserve_quota_nblks(tp, ip, resblks, 0,
> + XFS_QMOPT_RES_REGBLKS);
> if (error)
> goto out_trans_cancel;
>
> + xfs_trans_ijoin(tp, ip, 0);
> +
> + xfs_defer_init(&dfops, &first_block);
> + nimaps = 1;
> + error = xfs_bmapi_write(tp, ip, *offset_fsb, end_fsb - *offset_fsb,
> + XFS_BMAPI_COWFORK, &first_block, resblks, &imap,
> + &nimaps, &dfops);
> + if (error)
> + goto out_bmap_cancel;
> +
> error = xfs_defer_finish(&tp, &dfops, NULL);
> if (error)
> - goto out_trans_cancel;
> + goto out_bmap_cancel;
>
> error = xfs_trans_commit(tp);
> + if (error)
> + goto out_unlock;
>
> *offset_fsb = imap.br_startoff + imap.br_blockcount;
> +
> out_unlock:
> - xfs_iunlock(ip, XFS_ILOCK_EXCL);
> + xfs_iunlock(ip, lockmode);
> return error;
> -out_trans_cancel:
> +
> +out_bmap_cancel:
> xfs_defer_cancel(&dfops);
> + xfs_trans_unreserve_quota_nblks(tp, ip, (long)resblks, 0,
> + XFS_QMOPT_RES_REGBLKS);
> +out_trans_cancel:
> xfs_trans_cancel(tp);
> goto out_unlock;
> }
> --
> 2.1.4
>
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