Re: [PATCH v3 06/11] xfs: use and update the finobt on inode allocation

[Dave Chinner <david@fromorbit.com>]

On Tue, Feb 04, 2014 at 12:49:37PM -0500, Brian Foster wrote:
> Replace xfs_dialloc_ag() with an implementation that looks for a
> record in the finobt. The finobt only tracks records with at least
> one free inode. This eliminates the need for the intra-ag scan in
> the original algorithm. Once the inode is allocated, update the
> finobt appropriately (possibly removing the record) as well as the
> inobt.
> 
> Move the original xfs_dialloc_ag() algorithm to
> xfs_dialloc_ag_slow() and fall back as such if finobt support is
> not enabled.
> 
> Signed-off-by: Brian Foster <bfoster@redhat.com>
> ---
>  fs/xfs/xfs_ialloc.c | 211 +++++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 210 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_ialloc.c b/fs/xfs/xfs_ialloc.c
> index bdaab76..afc9840 100644
> --- a/fs/xfs/xfs_ialloc.c
> +++ b/fs/xfs/xfs_ialloc.c
> @@ -723,7 +723,7 @@ xfs_ialloc_get_rec(
>   * available.
>   */
>  STATIC int
> -xfs_dialloc_ag(
> +xfs_dialloc_ag_slow(
>  	struct xfs_trans	*tp,
>  	struct xfs_buf		*agbp,
>  	xfs_ino_t		parent,

OK, though I would have called it xfs_dialloc_ag_from_inobt() or
something similar to indicate what tree it is walking....

> +STATIC int
> +xfs_dialloc_ag(
> +	struct xfs_trans	*tp,
> +	struct xfs_buf		*agbp,
> +	xfs_ino_t		parent,
> +	xfs_ino_t		*inop)
> +{

Initial thought: Wow, long, long function. How can we split this up?

> +	struct xfs_mount		*mp = tp->t_mountp;
> +	struct xfs_agi			*agi = XFS_BUF_TO_AGI(agbp);
> +	xfs_agnumber_t			agno = be32_to_cpu(agi->agi_seqno);
> +	xfs_agnumber_t			pagno = XFS_INO_TO_AGNO(mp, parent);
> +	xfs_agino_t			pagino = XFS_INO_TO_AGINO(mp, parent);
> +	struct xfs_perag		*pag;
> +	struct xfs_btree_cur		*cur;
> +	struct xfs_btree_cur		*tcur;
> +	struct xfs_inobt_rec_incore	rec;
> +	struct xfs_inobt_rec_incore	trec;
> +	xfs_ino_t			ino;
> +	int				error;
> +	int				offset;
> +	int				i, j;
> +
> +	if (!xfs_sb_version_hasfinobt(&mp->m_sb))
> +		return xfs_dialloc_ag_slow(tp, agbp, parent, inop);
> +
> +	pag = xfs_perag_get(mp, agno);
> +
> +	/*
> +	 * If pagino is 0 (this is the root inode allocation) use newino.
> +	 * This must work because we've just allocated some.
> +	 */
> +	if (!pagino)
> +		pagino = be32_to_cpu(agi->agi_newino);
> +
> +	cur = xfs_inobt_init_cursor(mp, tp, agbp, agno, XFS_BTNUM_FINO);
> +
> +	error = xfs_check_agi_freecount(cur, agi);
> +	if (error)
> +		goto error_cur;
> +
> +	if (agno == pagno) {
> +		/*
> +		 * We're in the same AG as the parent inode so allocate the
> +		 * closest inode to the parent.
> +		 */
> +		error = xfs_inobt_lookup(cur, pagino, XFS_LOOKUP_LE, &i);
> +		if (error)
> +			goto error_cur;
> +		if (i == 1) {
> +			error = xfs_inobt_get_rec(cur, &rec, &i);
> +			if (error)
> +				goto error_cur;
> +			XFS_WANT_CORRUPTED_GOTO(i == 1, error_cur);
> +
> +			/*
> +			 * See if we've landed in the parent inode record. The
> +			 * finobt only tracks chunks with at least one free
> +			 * inode, so record existence is enough.
> +			 */
> +			if (pagino >= rec.ir_startino &&
> +			    pagino < (rec.ir_startino + XFS_INODES_PER_CHUNK))
> +				goto alloc_inode;
> +		}
> +
> +		error = xfs_btree_dup_cursor(cur, &tcur);
> +		if (error) 
> +			goto error_cur;
> +
> +		error = xfs_inobt_lookup(tcur, pagino, XFS_LOOKUP_GE, &j);
> +		if (error)
> +			goto error_tcur;
> +		if (j == 1) {
> +			error = xfs_inobt_get_rec(tcur, &trec, &j);
> +			if (error)
> +				goto error_tcur;
> +			XFS_WANT_CORRUPTED_GOTO(j == 1, error_tcur);
> +		}
> +
> +		if (i == 1 && j == 1) {
> +			if ((pagino - rec.ir_startino + XFS_INODES_PER_CHUNK - 1) >
> +			    (trec.ir_startino - pagino)) {
> +				rec = trec;
> +				xfs_btree_del_cursor(cur, XFS_BTREE_NOERROR);
> +				cur = tcur;
> +			} else {
> +				xfs_btree_del_cursor(tcur, XFS_BTREE_NOERROR);
> +			}
> +		} else if (j == 1) {
> +			rec = trec;
> +			xfs_btree_del_cursor(cur, XFS_BTREE_NOERROR);
> +			cur = tcur;
> +		} else {
> +			xfs_btree_del_cursor(tcur, XFS_BTREE_NOERROR);
> +		}

That entire branch can be easily factored into:

		error = xfs_dialloc_ag_finobt_near(cur, pagino, &rec);

/*
 * Allocate as close to the target agino as possible
 */
static int
xfs_dialloc_ag_finobt_near(
	struct xfs_btree_cur	*cur,
	xfs_agino_t		agino,
	struct xfs_inobt_rec_incore *rec)
{
	struct xfs_btree_cur	*rcur;	/* cursor for right search */
	struct xfs_inobt_rec_incore rrec; /* and the record used */
	int		error;
	int		i;
	int		l;

	error = xfs_inobt_lookup(cur, agino, XFS_LOOKUP_LE, &i);
	if (error)
		return error;

	if (i == 1) {
		error = xfs_inobt_get_rec(cur, rec, &i);
		if (error)
			return error;
		XFS_WANT_CORRUPTED_RETURN(i == 1);

		/*
		 * See if we've landed in the target inode record. The
		 * finobt only tracks chunks with at least one free
		 * inode, so record existence is enough.
		 */
		if (agino >= rec->ir_startino &&
		    agino < (rec->ir_startino + XFS_INODES_PER_CHUNK))
			return 0;
	}

	error = xfs_btree_dup_cursor(cur, &rcur);
	if (error)
		return error;

	error = xfs_inobt_lookup(rcur, agino, XFS_LOOKUP_GE, &j);
	if (error)
		goto error_rcur;
	if (j == 1) {
		error = xfs_inobt_get_rec(rcur, &rrec, &j);
		if (error)
			goto error_rcur;
		XFS_WANT_CORRUPTED_GOTO(j == 1, error_rcur);
	}

	if (i == 1 && j == 1) {
		/*
		 * both left and right records are valid, so choose
		 * the closer inode chunk to the target.
		 */
		if ((agino - rec.ir_startino + XFS_INODES_PER_CHUNK - 1) >
					(rrec.ir_startino - agino)) {
			*rec = rrec;
			xfs_btree_del_cursor(cur, XFS_BTREE_NOERROR);
			cur = rcur;
		} else {
			xfs_btree_del_cursor(rcur, XFS_BTREE_NOERROR);
		}
	} else if (j == 1) {
		/* only right record is valid */
		*rec = rrec;
		xfs_btree_del_cursor(cur, XFS_BTREE_NOERROR);
		cur = rcur;
	} else {
		/* Found neither left nor right.
		xfs_btree_del_cursor(rcur, XFS_BTREE_NOERROR);
	}
	return 0;

error_rcur:
	xfs_btree_del_cursor(rcur, XFS_BTREE_ERROR);
	return error;
}

> +	} else {
> +		/*
> +		 * Different AG from the parent inode. Check the record for the
> +		 * most recently allocated inode.
> +		 */
> +		if (agi->agi_newino != cpu_to_be32(NULLAGINO)) {
> +			error = xfs_inobt_lookup(cur, agi->agi_newino,
> +						 XFS_LOOKUP_EQ, &i);
> +			if (error)
> +				goto error_cur;
> +			if (i == 1) {
> +				error = xfs_inobt_get_rec(cur, &rec, &i);
> +				if (error)
> +					goto error_cur;
> +				XFS_WANT_CORRUPTED_GOTO(i == 1, error_cur);
> +				goto alloc_inode;
> +			}
> +		}
> +
> +		/*
> +		 * Allocate the first inode available in the AG.
> +		 */
> +		error = xfs_inobt_lookup(cur, 0, XFS_LOOKUP_GE, &i);
> +		if (error)
> +			goto error_cur;
> +		XFS_WANT_CORRUPTED_GOTO(i == 1, error_cur);
> +
> +		error = xfs_inobt_get_rec(cur, &rec, &i);
> +		if (error)
> +			goto error_cur;
> +		XFS_WANT_CORRUPTED_GOTO(i == 1, error_cur);

And that can be factored in a similar manner in
xfs_dialloc_ag_newino()....

> +	}
> +
> +alloc_inode:
> +	offset = xfs_lowbit64(rec.ir_free);
> +	ASSERT(offset >= 0);
> +	ASSERT(offset < XFS_INODES_PER_CHUNK);
> +	ASSERT((XFS_AGINO_TO_OFFSET(mp, rec.ir_startino) %
> +				   XFS_INODES_PER_CHUNK) == 0);
> +	ino = XFS_AGINO_TO_INO(mp, agno, rec.ir_startino + offset);
> +
> +	/*
> +	 * Modify or remove the finobt record.
> +	 */
> +	rec.ir_free &= ~XFS_INOBT_MASK(offset);
> +	rec.ir_freecount--;
> +	if (rec.ir_freecount) 
> +		error = xfs_inobt_update(cur, &rec);
> +	else
> +		error = xfs_btree_delete(cur, &i);
> +	if (error)
> +		goto error_cur;
> +
> +	/*
> +	 * Lookup and modify the equivalent record in the inobt.
> +	 */
> +	tcur = xfs_inobt_init_cursor(mp, tp, agbp, agno, XFS_BTNUM_INO);

In case ou hadn't guessed, I don't like the "tcur/trec" variables
because they make me thing "temporary" which they aren't. In this
case it is the inobt cursor and record....

In fact, this whole segment could be factored into a function like
xfs_dialloc_ag_inobt_update(), hence removing the second cursor from
xfs_dialloc_ag() function altogether and that would clean a lot of
the logic up....

> +
> +	error = xfs_check_agi_freecount(tcur, agi);
> +	if (error)
> +		goto error_tcur;
> +
> +	error = xfs_inobt_lookup(tcur, rec.ir_startino, XFS_LOOKUP_EQ, &i);
> +	if (error)
> +		goto error_tcur;
> +	XFS_WANT_CORRUPTED_GOTO(i == 1, error_tcur);
> +
> +	error = xfs_inobt_get_rec(tcur, &trec, &i);
> +	if (error)
> +		goto error_tcur;
> +	XFS_WANT_CORRUPTED_GOTO(i == 1, error_tcur);
> +	ASSERT((XFS_AGINO_TO_OFFSET(mp, trec.ir_startino) %
> +				   XFS_INODES_PER_CHUNK) == 0);
> +
> +	trec.ir_free &= ~XFS_INOBT_MASK(offset);
> +	trec.ir_freecount--;
> +
> +	XFS_WANT_CORRUPTED_GOTO((rec.ir_free == trec.ir_free) &&
> +				(rec.ir_freecount == trec.ir_freecount),
> +				error_tcur);
> +
> +	error = xfs_inobt_update(tcur, &trec);
> +	if (error)
> +		goto error_tcur;
> +
> +	/*
> +	 * Update the perag and superblock.
> +	 */
> +	be32_add_cpu(&agi->agi_freecount, -1);
> +	xfs_ialloc_log_agi(tp, agbp, XFS_AGI_FREECOUNT);
> +	pag->pagi_freecount--;
> +
> +	xfs_trans_mod_sb(tp, XFS_TRANS_SB_IFREE, -1);

This will need to be done before you update the inobt, though, so
you can run the xfs_check_agi_freecount() count in it and it will
come out correct....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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