Re: [PATCH 4/9] xfs_repair: rebuild free space btrees with bulk loader

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Thu, May 28, 2020 at 11:10:44AM -0400, Brian Foster wrote:
> On Tue, May 19, 2020 at 06:51:08PM -0700, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@oracle.com>
> > 
> > Use the btree bulk loading functions to rebuild the free space btrees
> > and drop the open-coded implementation.
> > 
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > ---
> >  libxfs/libxfs_api_defs.h |    3 
> >  repair/phase5.c          |  870 +++++++++++++---------------------------------
> >  2 files changed, 254 insertions(+), 619 deletions(-)
> > 
> > 
> ...
> > diff --git a/repair/phase5.c b/repair/phase5.c
> > index 8f5e5f59..e69b042c 100644
> > --- a/repair/phase5.c
> > +++ b/repair/phase5.c
> ...
> > @@ -837,268 +567,202 @@ btnum_to_ops(
> ...
> > +static void
> > +init_freespace_cursors(
> > +	struct repair_ctx	*sc,
> > +	xfs_agnumber_t		agno,
> > +	unsigned int		free_space,
> > +	unsigned int		*nr_extents,
> > +	int			*extra_blocks,
> > +	struct bt_rebuild	*btr_bno,
> > +	struct bt_rebuild	*btr_cnt)
> >  {
> > -	xfs_agnumber_t		i;
> > -	xfs_agblock_t		j;
> > -	struct xfs_btree_block	*bt_hdr;
> > -	xfs_alloc_rec_t		*bt_rec;
> > -	int			level;
> > -	xfs_agblock_t		agbno;
> > -	extent_tree_node_t	*ext_ptr;
> > -	bt_stat_level_t		*lptr;
> > -	xfs_extlen_t		freeblks;
> > -	const struct xfs_buf_ops *ops = btnum_to_ops(btnum);
> > +	unsigned int		bno_blocks;
> > +	unsigned int		cnt_blocks;
> >  	int			error;
> >  
> > -	ASSERT(btnum == XFS_BTNUM_BNO || btnum == XFS_BTNUM_CNT);
> > -
> > -#ifdef XR_BLD_FREE_TRACE
> > -	fprintf(stderr, "in build_freespace_tree, agno = %d\n", agno);
> > -#endif
> > -	level = btree_curs->num_levels;
> > -	freeblks = 0;
> > +	init_rebuild(sc, &XFS_RMAP_OINFO_AG, free_space, btr_bno);
> > +	init_rebuild(sc, &XFS_RMAP_OINFO_AG, free_space, btr_cnt);
> >  
> > -	ASSERT(level > 0);
> > +	btr_bno->cur = libxfs_allocbt_stage_cursor(sc->mp,
> > +			&btr_bno->newbt.afake, agno, XFS_BTNUM_BNO);
> > +	btr_cnt->cur = libxfs_allocbt_stage_cursor(sc->mp,
> > +			&btr_cnt->newbt.afake, agno, XFS_BTNUM_CNT);
> >  
> >  	/*
> > -	 * initialize the first block on each btree level
> > +	 * Now we need to allocate blocks for the free space btrees using the
> > +	 * free space records we're about to put in them.  Every record we use
> > +	 * can change the shape of the free space trees, so we recompute the
> > +	 * btree shape until we stop needing /more/ blocks.  If we have any
> > +	 * left over we'll stash them in the AGFL when we're done.
> >  	 */
> > -	for (i = 0; i < level; i++)  {
> > -		lptr = &btree_curs->level[i];
> > +	do {
> > +		unsigned int	num_freeblocks;
> > +
> > +		bno_blocks = btr_bno->bload.nr_blocks;
> > +		cnt_blocks = btr_cnt->bload.nr_blocks;
> >  
> > -		agbno = get_next_blockaddr(agno, i, btree_curs);
> > -		error = -libxfs_buf_get(mp->m_dev,
> > -				XFS_AGB_TO_DADDR(mp, agno, agbno),
> > -				XFS_FSB_TO_BB(mp, 1), &lptr->buf_p);
> > +		/* Compute how many bnobt blocks we'll need. */
> > +		error = -libxfs_btree_bload_compute_geometry(btr_bno->cur,
> > +				&btr_bno->bload, *nr_extents);
> >  		if (error)
> >  			do_error(
> ...
> > +_("Unable to compute free space by block btree geometry, error %d.\n"), -error);
> > +
> > +		/* Compute how many cntbt blocks we'll need. */
> > +		error = -libxfs_btree_bload_compute_geometry(btr_bno->cur,
> 
> btr_cnt?							^

Ooops, yes.  Fixed.

> > +				&btr_cnt->bload, *nr_extents);
> > +		if (error)
> > +			do_error(
> > +_("Unable to compute free space by length btree geometry, error %d.\n"), -error);
> > +
> > +		/* We don't need any more blocks, so we're done. */
> > +		if (bno_blocks >= btr_bno->bload.nr_blocks &&
> > +		    cnt_blocks >= btr_cnt->bload.nr_blocks)
> > +			break;
> > +
> > +		/* Allocate however many more blocks we need this time. */
> > +		if (bno_blocks < btr_bno->bload.nr_blocks)
> > +			setup_rebuild(sc->mp, agno, btr_bno,
> > +					btr_bno->bload.nr_blocks - bno_blocks);
> > +		if (cnt_blocks < btr_cnt->bload.nr_blocks)
> > +			setup_rebuild(sc->mp, agno, btr_cnt,
> > +					btr_cnt->bload.nr_blocks - cnt_blocks);
> 
> Hmm, I find the setup_rebuild() name a little confusing when seeing an
> init_rebuild() used in the same function. The difference is not apparent
> at a glance. Could we rename setup_rebuild() to something more specific?
> reserve_blocks() perhaps?

Ok, renamed.

> > +
> > +		/* Ok, now how many free space records do we have? */
> > +		*nr_extents = count_bno_extents_blocks(agno, &num_freeblocks);
> > +	} while (1);
> > +
> > +	*extra_blocks = (bno_blocks - btr_bno->bload.nr_blocks) +
> > +			(cnt_blocks - btr_cnt->bload.nr_blocks);
> > +}
> > +
> > +static void
> > +get_freesp_data(
> > +	struct xfs_btree_cur		*cur,
> > +	struct extent_tree_node		*bno_rec,
> > +	xfs_agblock_t			*freeblks)
> > +{
> > +	struct xfs_alloc_rec_incore	*arec = &cur->bc_rec.a;
> > +
> > +	arec->ar_startblock = bno_rec->ex_startblock;
> > +	arec->ar_blockcount = bno_rec->ex_blockcount;
> > +	if (freeblks)
> > +		*freeblks += bno_rec->ex_blockcount;
> > +}
> > +
> > +/* Grab one bnobt record. */
> > +static int
> > +get_bnobt_record(
> > +	struct xfs_btree_cur		*cur,
> > +	void				*priv)
> > +{
> > +	struct bt_rebuild		*btr = priv;
> > +
> > +	get_freesp_data(cur, btr->bno_rec, btr->freeblks);
> > +	btr->bno_rec = findnext_bno_extent(btr->bno_rec);
> 
> We should probably check for NULL here even if we don't expect it to
> happen.
> 
> Also, this logic where we load the current pointer and get the next had
> my eyes crossed for a bit. Can we just check the pointer state here to
> determine whether to find the first record or the next?

Hm, I did that, and the logic ends up more cluttered looking:

	if (cur->bc_btnum == XFS_BTNUM_BNO) {
		if (btr->bno_rec == NULL)
			btr->bno_rec = findfirst_bno_extent(agno);
		else
			btr->bno_rec = findnext_bno_extent(btr->bno_rec);
	} else {
		if (btr->bno_rec == NULL)
			btr->bno_rec = findfirst_bcnt_extent(agno);
		else
			btr->bno_rec = findnext_bcnt_extent(cur->bc_ag.agno,
							    btr->bno_rec);
	}

OTOH I think you do have a good point that splitting the code that sets
bno_rec across three functions is not easy to understand.

> Finally, I notice we duplicate the build_[bno|cnt]bt() functions for
> what amounts to a different get_record() callback specific to the tree
> type. If we also generalize get_record() to use the tree type (it
> already has the cursor), it seems that much of the duplication can be
> reduced and the logic simplified.

Ok, done.

> > +	return 0;
> > +}
> > +
> > +/* Rebuild a free space by block number btree. */
> > +static void
> > +build_bnobt(
> > +	struct repair_ctx	*sc,
> > +	xfs_agnumber_t		agno,
> > +	struct bt_rebuild	*btr_bno,
> > +	xfs_agblock_t		*freeblks)
> > +{
> > +	int			error;
> > +
> > +	*freeblks = 0;
> > +	btr_bno->bload.get_record = get_bnobt_record;
> > +	btr_bno->bload.claim_block = rebuild_claim_block;
> 
> Note that one of these callbacks is introduced in this patch and the
> other in the previous. I've no issue with splitting the patches as noted
> in the previous patch, but these should probably be consistent one way
> or the other.

All the btree types set ->claim_block to rebuild_claim_block, whereas
->get_record is specific to the particular type of btree.

> > +	btr_bno->bno_rec = findfirst_bno_extent(agno);
> > +	btr_bno->freeblks = freeblks;
> > +
> > +	error = -libxfs_trans_alloc_empty(sc->mp, &sc->tp);
> > +	if (error)
> > +		do_error(
> > +_("Insufficient memory to construct bnobt rebuild transaction.\n"));
> > +
> > +	/* Add all observed bnobt records. */
> > +	error = -libxfs_btree_bload(btr_bno->cur, &btr_bno->bload, btr_bno);
> > +	if (error)
> > +		do_error(
> > +_("Error %d while creating bnobt btree for AG %u.\n"), error, agno);
> > +
> > +	/* Since we're not writing the AGF yet, no need to commit the cursor */
> > +	libxfs_btree_del_cursor(btr_bno->cur, 0);
> > +	error = -libxfs_trans_commit(sc->tp);
> > +	if (error)
> > +		do_error(
> > +_("Error %d while writing bnobt btree for AG %u.\n"), error, agno);
> > +	sc->tp = NULL;
> > +}
> > +
> ...
> > @@ -2354,48 +2041,14 @@ build_agf_agfl(
> >  			freelist[i] = cpu_to_be32(NULLAGBLOCK);
> >  	}
> >  
> > -	/*
> > -	 * do we have left-over blocks in the btree cursors that should
> > -	 * be used to fill the AGFL?
> > -	 */
> > -	if (bno_bt->num_free_blocks > 0 || bcnt_bt->num_free_blocks > 0)  {
> > -		/*
> > -		 * yes, now grab as many blocks as we can
> > -		 */
> > -		i = 0;
> > -		while (bno_bt->num_free_blocks > 0 && i < libxfs_agfl_size(mp))
> > -		{
> > -			freelist[i] = cpu_to_be32(
> > -					get_next_blockaddr(agno, 0, bno_bt));
> > -			i++;
> > -		}
> > -
> > -		while (bcnt_bt->num_free_blocks > 0 && i < libxfs_agfl_size(mp))
> > -		{
> > -			freelist[i] = cpu_to_be32(
> > -					get_next_blockaddr(agno, 0, bcnt_bt));
> > -			i++;
> > -		}
> > -		/*
> > -		 * now throw the rest of the blocks away and complain
> > -		 */
> > -		while (bno_bt->num_free_blocks > 0) {
> > -			fsb = XFS_AGB_TO_FSB(mp, agno,
> > -					get_next_blockaddr(agno, 0, bno_bt));
> > -			error = slab_add(lost_fsb, &fsb);
> > -			if (error)
> > -				do_error(
> > -_("Insufficient memory saving lost blocks.\n"));
> > -		}
> > -		while (bcnt_bt->num_free_blocks > 0) {
> > -			fsb = XFS_AGB_TO_FSB(mp, agno,
> > -					get_next_blockaddr(agno, 0, bcnt_bt));
> > -			error = slab_add(lost_fsb, &fsb);
> > -			if (error)
> > -				do_error(
> > -_("Insufficient memory saving lost blocks.\n"));
> > -		}
> > +	/* Fill the AGFL with leftover blocks or save them for later. */
> > +	i = 0;
> 
> How about agfl_idx or something since this variable is passed down into
> a function?

The 'i' variable existed before this patch.  I can add a new cleanup to
fix the name...

> > +	freelist = xfs_buf_to_agfl_bno(agfl_buf);
> > +	fill_agfl(btr_bno, freelist, &i);
> > +	fill_agfl(btr_cnt, freelist, &i);
> >  
> > +	/* Set the AGF counters for the AGFL. */
> > +	if (i > 0) {
> >  		agf->agf_flfirst = 0;
> >  		agf->agf_fllast = cpu_to_be32(i - 1);
> >  		agf->agf_flcount = cpu_to_be32(i);
> ...
> > @@ -2650,9 +2283,9 @@ _("unable to rebuild AG %u.  Not enough free space in on-disk AG.\n"),
> >  	/*
> >  	 * set up agf and agfl
> >  	 */
> > -	build_agf_agfl(mp, agno, &bno_btree_curs,
> > -		&bcnt_btree_curs, freeblks1, extra_blocks,
> > -		&rmap_btree_curs, &refcnt_btree_curs, lost_fsb);
> > +	build_agf_agfl(mp, agno, &btr_bno, &btr_cnt, freeblks1, extra_blocks,
> > +			&rmap_btree_curs, &refcnt_btree_curs, lost_fsb);
> > +
> 
> I was trying to figure out what extra_blocks was used for and noticed
> that it's not even used by this function. Perhaps a preceding cleanup
> patch to drop it?

Ok.

> >  	/*
> >  	 * build inode allocation tree.
> >  	 */
> > @@ -2674,15 +2307,14 @@ _("unable to rebuild AG %u.  Not enough free space in on-disk AG.\n"),
> >  	/*
> >  	 * tear down cursors
> >  	 */
> > -	finish_cursor(&bno_btree_curs);
> > -	finish_cursor(&ino_btree_curs);
> 
> Looks like this one shouldn't be going away here.

Oops, good catch.

--D

> Brian
> 
> > +	finish_rebuild(mp, &btr_bno, lost_fsb);
> > +	finish_rebuild(mp, &btr_cnt, lost_fsb);
> >  	if (xfs_sb_version_hasrmapbt(&mp->m_sb))
> >  		finish_cursor(&rmap_btree_curs);
> >  	if (xfs_sb_version_hasreflink(&mp->m_sb))
> >  		finish_cursor(&refcnt_btree_curs);
> >  	if (xfs_sb_version_hasfinobt(&mp->m_sb))
> >  		finish_cursor(&fino_btree_curs);
> > -	finish_cursor(&bcnt_btree_curs);
> >  
> >  	/*
> >  	 * release the incore per-AG bno/bcnt trees so the extent nodes
> > 
>