Re: [PATCH v5 05/11] xfs: refactor cntbt lastblock scan best extent logic into helper

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

On Fri, Sep 27, 2019 at 01:17:56PM -0400, Brian Foster wrote:
> The cntbt lastblock scan checks the size, alignment, locality, etc.
> of each free extent in the block and compares it with the current
> best candidate. This logic will be reused by the upcoming optimized
> cntbt algorithm, so refactor it into a separate helper. Note that
> acur->diff is now initialized to -1 (unsigned) instead of 0 to
> support the more granular comparison logic in the new helper.
> 
> Signed-off-by: Brian Foster <bfoster@redhat.com>

Looks ok,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> ---
>  fs/xfs/libxfs/xfs_alloc.c | 115 ++++++++++++++++++++++++++++----------
>  fs/xfs/xfs_trace.h        |  26 +++++++++
>  2 files changed, 113 insertions(+), 28 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
> index 4514a059486e..38183953636a 100644
> --- a/fs/xfs/libxfs/xfs_alloc.c
> +++ b/fs/xfs/libxfs/xfs_alloc.c
> @@ -744,7 +744,7 @@ xfs_alloc_cur_setup(
>  	acur->rec_len = 0;
>  	acur->bno = 0;
>  	acur->len = 0;
> -	acur->diff = 0;
> +	acur->diff = -1;
>  	acur->busy = false;
>  	acur->busy_gen = 0;
>  
> @@ -791,6 +791,89 @@ xfs_alloc_cur_close(
>  	acur->cnt = acur->bnolt = acur->bnogt = NULL;
>  }
>  
> +/*
> + * Check an extent for allocation and track the best available candidate in the
> + * allocation structure. The cursor is deactivated if it has entered an out of
> + * range state based on allocation arguments. Optionally return the extent
> + * extent geometry and allocation status if requested by the caller.
> + */
> +static int
> +xfs_alloc_cur_check(
> +	struct xfs_alloc_arg	*args,
> +	struct xfs_alloc_cur	*acur,
> +	struct xfs_btree_cur	*cur,
> +	int			*new)
> +{
> +	int			error, i;
> +	xfs_agblock_t		bno, bnoa, bnew;
> +	xfs_extlen_t		len, lena, diff = -1;
> +	bool			busy;
> +	unsigned		busy_gen = 0;
> +	bool			deactivate = false;
> +
> +	*new = 0;
> +
> +	error = xfs_alloc_get_rec(cur, &bno, &len, &i);
> +	if (error)
> +		return error;
> +	XFS_WANT_CORRUPTED_RETURN(args->mp, i == 1);
> +
> +	/*
> +	 * Check minlen and deactivate a cntbt cursor if out of acceptable size
> +	 * range (i.e., walking backwards looking for a minlen extent).
> +	 */
> +	if (len < args->minlen) {
> +		deactivate = true;
> +		goto out;
> +	}
> +
> +	busy = xfs_alloc_compute_aligned(args, bno, len, &bnoa, &lena,
> +					 &busy_gen);
> +	acur->busy |= busy;
> +	if (busy)
> +		acur->busy_gen = busy_gen;
> +	/* deactivate a bnobt cursor outside of locality range */
> +	if (bnoa < args->min_agbno || bnoa > args->max_agbno)
> +		goto out;
> +	if (lena < args->minlen)
> +		goto out;
> +
> +	args->len = XFS_EXTLEN_MIN(lena, args->maxlen);
> +	xfs_alloc_fix_len(args);
> +	ASSERT(args->len >= args->minlen);
> +	if (args->len < acur->len)
> +		goto out;
> +
> +	/*
> +	 * We have an aligned record that satisfies minlen and beats or matches
> +	 * the candidate extent size. Compare locality for near allocation mode.
> +	 */
> +	ASSERT(args->type == XFS_ALLOCTYPE_NEAR_BNO);
> +	diff = xfs_alloc_compute_diff(args->agbno, args->len,
> +				      args->alignment, args->datatype,
> +				      bnoa, lena, &bnew);
> +	if (bnew == NULLAGBLOCK)
> +		goto out;
> +	if (diff > acur->diff)
> +		goto out;
> +
> +	ASSERT(args->len > acur->len ||
> +	       (args->len == acur->len && diff <= acur->diff));
> +	acur->rec_bno = bno;
> +	acur->rec_len = len;
> +	acur->bno = bnew;
> +	acur->len = args->len;
> +	acur->diff = diff;
> +	*new = 1;
> +
> +out:
> +	if (deactivate)
> +		cur->bc_private.a.priv.abt.active = false;
> +	trace_xfs_alloc_cur_check(args->mp, cur->bc_btnum, bno, len, diff,
> +				  *new);
> +	return 0;
> +}
> +
>  /*
>   * Deal with the case where only small freespaces remain. Either return the
>   * contents of the last freespace record, or allocate space from the freelist if
> @@ -1257,8 +1340,6 @@ xfs_alloc_ag_vextent_near(
>  	 * but we never loop back to the top.
>  	 */
>  	while (xfs_btree_islastblock(acur.cnt, 0)) {
> -		xfs_extlen_t	diff;
> -
>  #ifdef DEBUG
>  		if (dofirst)
>  			break;
> @@ -1289,38 +1370,16 @@ xfs_alloc_ag_vextent_near(
>  		}
>  		i = acur.cnt->bc_ptrs[0];
>  		for (j = 1;
> -		     !error && j && (acur.len < args->maxlen || acur.diff > 0);
> +		     !error && j && xfs_alloc_cur_active(acur.cnt) &&
> +		     (acur.len < args->maxlen || acur.diff > 0);
>  		     error = xfs_btree_increment(acur.cnt, 0, &j)) {
>  			/*
>  			 * For each entry, decide if it's better than
>  			 * the previous best entry.
>  			 */
> -			error = xfs_alloc_get_rec(acur.cnt, &ltbno, &ltlen, &i);
> +			error = xfs_alloc_cur_check(args, &acur, acur.cnt, &i);
>  			if (error)
>  				goto out;
> -			XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, out);
> -			acur.busy = xfs_alloc_compute_aligned(args, ltbno, ltlen,
> -					&ltbnoa, &ltlena, &acur.busy_gen);
> -			if (ltlena < args->minlen)
> -				continue;
> -			if (ltbnoa < args->min_agbno || ltbnoa > args->max_agbno)
> -				continue;
> -			args->len = XFS_EXTLEN_MIN(ltlena, args->maxlen);
> -			xfs_alloc_fix_len(args);
> -			ASSERT(args->len >= args->minlen);
> -			if (args->len < acur.len)
> -				continue;
> -			diff = xfs_alloc_compute_diff(args->agbno, args->len,
> -				args->alignment, args->datatype, ltbnoa,
> -				ltlena, &ltnew);
> -			if (ltnew != NULLAGBLOCK &&
> -			    (args->len > acur.len || diff < acur.diff)) {
> -				acur.rec_bno = ltbno;
> -				acur.rec_len = ltlen;
> -				acur.diff = diff;
> -				acur.bno = ltnew;
> -				acur.len = args->len;
> -			}
>  		}
>  		/*
>  		 * It didn't work.  We COULD be in a case where
> diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
> index eaae275ed430..cf618919cacf 100644
> --- a/fs/xfs/xfs_trace.h
> +++ b/fs/xfs/xfs_trace.h
> @@ -1663,6 +1663,32 @@ DEFINE_ALLOC_EVENT(xfs_alloc_vextent_noagbp);
>  DEFINE_ALLOC_EVENT(xfs_alloc_vextent_loopfailed);
>  DEFINE_ALLOC_EVENT(xfs_alloc_vextent_allfailed);
>  
> +TRACE_EVENT(xfs_alloc_cur_check,
> +	TP_PROTO(struct xfs_mount *mp, xfs_btnum_t btnum, xfs_agblock_t bno,
> +		 xfs_extlen_t len, xfs_extlen_t diff, bool new),
> +	TP_ARGS(mp, btnum, bno, len, diff, new),
> +	TP_STRUCT__entry(
> +		__field(dev_t, dev)
> +		__field(xfs_btnum_t, btnum)
> +		__field(xfs_agblock_t, bno)
> +		__field(xfs_extlen_t, len)
> +		__field(xfs_extlen_t, diff)
> +		__field(bool, new)
> +	),
> +	TP_fast_assign(
> +		__entry->dev = mp->m_super->s_dev;
> +		__entry->btnum = btnum;
> +		__entry->bno = bno;
> +		__entry->len = len;
> +		__entry->diff = diff;
> +		__entry->new = new;
> +	),
> +	TP_printk("dev %d:%d btree %s bno 0x%x len 0x%x diff 0x%x new %d",
> +		  MAJOR(__entry->dev), MINOR(__entry->dev),
> +		  __print_symbolic(__entry->btnum, XFS_BTNUM_STRINGS),
> +		  __entry->bno, __entry->len, __entry->diff, __entry->new)
> +)
> +
>  DECLARE_EVENT_CLASS(xfs_da_class,
>  	TP_PROTO(struct xfs_da_args *args),
>  	TP_ARGS(args),
> -- 
> 2.20.1
>