xfs: reuse best extent tracking logic for bnobt scan

The near mode bnobt scan searches left and right in the bnobt
looking for the closest free extent to the allocation hint that
satisfies minlen. Once such an extent is found, the left/right
search terminates, we search one more time in the opposite direction
and finish the allocation with the best overall extent.

The left/right and find best searches are currently controlled via a
combination of cursor state and local variables. Clean up this code
and prepare for further improvements to the near mode fallback
algorithm by reusing the allocation cursor best extent tracking
mechanism. Update the tracking logic to deactivate bnobt cursors
when out of allocation range and replace open-coded extent checks to
calls to the common helper. In doing so, rename some misnamed local
variables in the top-level near mode allocation function.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

2 files changed, 79 insertions, 201 deletions

diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
index 3481489622ed..2b40842ef5f6 100644
--- a/fs/xfs/libxfs/xfs_alloc.c
+++ b/fs/xfs/libxfs/xfs_alloc.c
@@ -810,6 +810,7 @@ xfs_alloc_cur_check(
 	bool			busy;
 	unsigned		busy_gen = 0;
 	bool			deactivate = false;
+	bool			isbnobt = cur->bc_btnum == XFS_BTNUM_BNO;
 
 	*new = 0;
 
@@ -823,7 +824,7 @@ xfs_alloc_cur_check(
 	 * range (i.e., walking backwards looking for a minlen extent).
 	 */
 	if (len < args->minlen) {
-		deactivate = true;
+		deactivate = !isbnobt;
 		goto out;
 	}
 
@@ -833,8 +834,10 @@ xfs_alloc_cur_check(
 	if (busy)
 		acur->busy_gen = busy_gen;
 	/* deactivate a bnobt cursor outside of locality range */
-	if (bnoa < args->min_agbno || bnoa > args->max_agbno)
+	if (bnoa < args->min_agbno || bnoa > args->max_agbno) {
+		deactivate = isbnobt;
 		goto out;
+	}
 	if (lena < args->minlen)
 		goto out;
 
@@ -854,8 +857,14 @@ xfs_alloc_cur_check(
 				      bnoa, lena, &bnew);
 	if (bnew == NULLAGBLOCK)
 		goto out;
-	if (diff > acur->diff)
+
+	/*
+	 * Deactivate a bnobt cursor with worse locality than the current best.
+	 */
+	if (diff > acur->diff) {
+		deactivate = isbnobt;
 		goto out;
+	}
 
 	ASSERT(args->len > acur->len ||
 	       (args->len == acur->len && diff <= acur->diff));
@@ -1163,96 +1172,44 @@ error0:
 }
 
 /*
- * Search the btree in a given direction via the search cursor and compare
- * the records found against the good extent we've already found.
+ * Search the btree in a given direction and check the records against the good
+ * extent we've already found.
  */
 STATIC int
 xfs_alloc_find_best_extent(
-	struct xfs_alloc_arg	*args,	/* allocation argument structure */
-	struct xfs_btree_cur	*gcur,	/* good cursor */
-	struct xfs_btree_cur	*scur,	/* searching cursor */
-	xfs_agblock_t		gdiff,	/* difference for search comparison */
-	xfs_agblock_t		*sbno,	/* extent found by search */
-	xfs_extlen_t		*slen,	/* extent length */
-	xfs_agblock_t		*sbnoa,	/* aligned extent found by search */
-	xfs_extlen_t		*slena,	/* aligned extent length */
-	int			dir)	/* 0 = search right, 1 = search left */
+	struct xfs_alloc_arg	*args,
+	struct xfs_alloc_cur	*acur,
+	struct xfs_btree_cur	*cur,
+	bool			increment)
 {
-	xfs_agblock_t		new;
-	xfs_agblock_t		sdiff;
 	int			error;
 	int			i;
-	unsigned		busy_gen;
-
-	/* The good extent is perfect, no need to  search. */
-	if (!gdiff)
-		goto out_use_good;
 
 	/*
-	 * Look until we find a better one, run out of space or run off the end.
+	 * Search so long as the cursor is active or we find a better extent.
+	 * The cursor is deactivated if it extends beyond the range of the
+	 * current allocation candidate.
 	 */
-	do {
-		error = xfs_alloc_get_rec(scur, sbno, slen, &i);
+	while (xfs_alloc_cur_active(cur)) {
+		error = xfs_alloc_cur_check(args, acur, cur, &i);
 		if (error)
-			goto error0;
-		XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0);
-		xfs_alloc_compute_aligned(args, *sbno, *slen,
-				sbnoa, slena, &busy_gen);
-
-		/*
-		 * The good extent is closer than this one.
-		 */
-		if (!dir) {
-			if (*sbnoa > args->max_agbno)
-				goto out_use_good;
-			if (*sbnoa >= args->agbno + gdiff)
-				goto out_use_good;
-		} else {
-			if (*sbnoa < args->min_agbno)
-				goto out_use_good;
-			if (*sbnoa <= args->agbno - gdiff)
-				goto out_use_good;
-		}
-
-		/*
-		 * Same distance, compare length and pick the best.
-		 */
-		if (*slena >= args->minlen) {
-			args->len = XFS_EXTLEN_MIN(*slena, args->maxlen);
-			xfs_alloc_fix_len(args);
-
-			sdiff = xfs_alloc_compute_diff(args->agbno, args->len,
-						       args->alignment,
-						       args->datatype, *sbnoa,
-						       *slena, &new);
-
-			/*
-			 * Choose closer size and invalidate other cursor.
-			 */
-			if (sdiff < gdiff)
-				goto out_use_search;
-			goto out_use_good;
-		}
+			return error;
+		if (i == 1)
+			break;
+		if (!xfs_alloc_cur_active(cur))
+			break;
 
-		if (!dir)
-			error = xfs_btree_increment(scur, 0, &i);
+		if (increment)
+			error = xfs_btree_increment(cur, 0, &i);
 		else
-			error = xfs_btree_decrement(scur, 0, &i);
+			error = xfs_btree_decrement(cur, 0, &i);
 		if (error)
-			goto error0;
-	} while (i);
-
-out_use_good:
-	scur->bc_private.a.priv.abt.active = false;
-	return 0;
+			return error;
+		if (i == 0)
+			cur->bc_private.a.priv.abt.active = false;
+	}
 
-out_use_search:
-	gcur->bc_private.a.priv.abt.active = false;
 	return 0;
-
-error0:
-	/* caller invalidates cursors */
-	return error;
 }
 
 /*
@@ -1266,23 +1223,13 @@ xfs_alloc_ag_vextent_near(
 	struct xfs_alloc_arg	*args)
 {
 	struct xfs_alloc_cur	acur = {};
-	struct xfs_btree_cur	*bno_cur;
-	xfs_agblock_t	gtbno;		/* start bno of right side entry */
-	xfs_agblock_t	gtbnoa;		/* aligned ... */
-	xfs_extlen_t	gtdiff;		/* difference to right side entry */
-	xfs_extlen_t	gtlen;		/* length of right side entry */
-	xfs_extlen_t	gtlena;		/* aligned ... */
-	xfs_agblock_t	gtnew;		/* useful start bno of right side */
-	int		error;		/* error code */
-	int		i;		/* result code, temporary */
-	int		j;		/* result code, temporary */
-	xfs_agblock_t	ltbno;		/* start bno of left side entry */
-	xfs_agblock_t	ltbnoa;		/* aligned ... */
-	xfs_extlen_t	ltdiff;		/* difference to left side entry */
-	xfs_extlen_t	ltlen;		/* length of left side entry */
-	xfs_extlen_t	ltlena;		/* aligned ... */
-	xfs_agblock_t	ltnew;		/* useful start bno of left side */
-	xfs_extlen_t	rlen;		/* length of returned extent */
+	struct xfs_btree_cur	*fbcur = NULL;
+	int			error;		/* error code */
+	int			i;		/* result code, temporary */
+	int			j;		/* result code, temporary */
+	xfs_agblock_t		bno;
+	xfs_extlen_t		len;
+	bool			fbinc = false;
 #ifdef DEBUG
 	/*
 	 * Randomly don't execute the first algorithm.
@@ -1304,9 +1251,7 @@ xfs_alloc_ag_vextent_near(
 		args->agbno = args->max_agbno;
 
 restart:
-	ltlen = 0;
-	gtlena = 0;
-	ltlena = 0;
+	len = 0;
 
 	/*
 	 * Set up cursors and see if there are any free extents as big as
@@ -1315,11 +1260,11 @@ restart:
 	 */
 	error = xfs_alloc_cur_setup(args, &acur);
 	if (error == -ENOSPC) {
-		error = xfs_alloc_ag_vextent_small(args, acur.cnt, &ltbno,
-				&ltlen, &i);
+		error = xfs_alloc_ag_vextent_small(args, acur.cnt, &bno,
+				&len, &i);
 		if (error)
 			goto out;
-		if (i == 0 || ltlen == 0) {
+		if (i == 0 || len == 0) {
 			trace_xfs_alloc_near_noentry(args);
 			goto out;
 		}
@@ -1350,21 +1295,21 @@ restart:
 		 * record smaller than maxlen, go to the start of this block,
 		 * and skip all those smaller than minlen.
 		 */
-		if (ltlen || args->alignment > 1) {
+		if (len || args->alignment > 1) {
 			acur.cnt->bc_ptrs[0] = 1;
 			do {
-				error = xfs_alloc_get_rec(acur.cnt, &ltbno,
-						&ltlen, &i);
+				error = xfs_alloc_get_rec(acur.cnt, &bno, &len,
+						&i);
 				if (error)
 					goto out;
 				XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, out);
-				if (ltlen >= args->minlen)
+				if (len >= args->minlen)
 					break;
 				error = xfs_btree_increment(acur.cnt, 0, &i);
 				if (error)
 					goto out;
 			} while (i);
-			ASSERT(ltlen >= args->minlen);
+			ASSERT(len >= args->minlen);
 			if (!i)
 				break;
 		}
@@ -1433,77 +1378,43 @@ restart:
 	 */
 	do {
 		if (xfs_alloc_cur_active(acur.bnolt)) {
-			error = xfs_alloc_get_rec(acur.bnolt, &ltbno, &ltlen, &i);
+			error = xfs_alloc_cur_check(args, &acur, acur.bnolt, &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 && ltbnoa >= args->min_agbno)
+			if (i == 1) {
+				trace_xfs_alloc_cur_left(args);
+				fbcur = acur.bnogt;
+				fbinc = true;
 				break;
+			}
 			error = xfs_btree_decrement(acur.bnolt, 0, &i);
 			if (error)
 				goto out;
-			if (!i || ltbnoa < args->min_agbno)
+			if (!i)
 				acur.bnolt->bc_private.a.priv.abt.active = false;
 		}
 		if (xfs_alloc_cur_active(acur.bnogt)) {
-			error = xfs_alloc_get_rec(acur.bnogt, &gtbno, &gtlen, &i);
+			error = xfs_alloc_cur_check(args, &acur, acur.bnogt, &i);
 			if (error)
 				goto out;
-			XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, out);
-			acur.busy |= xfs_alloc_compute_aligned(args, gtbno,
-					gtlen, &gtbnoa, &gtlena, &acur.busy_gen);
-			if (gtlena >= args->minlen && gtbnoa <= args->max_agbno)
+			if (i == 1) {
+				trace_xfs_alloc_cur_right(args);
+				fbcur = acur.bnolt;
+				fbinc = false;
 				break;
+			}
 			error = xfs_btree_increment(acur.bnogt, 0, &i);
 			if (error)
 				goto out;
-			if (!i || gtbnoa > args->max_agbno)
+			if (!i)
 				acur.bnogt->bc_private.a.priv.abt.active = false;
 		}
 	} while (xfs_alloc_cur_active(acur.bnolt) ||
 		 xfs_alloc_cur_active(acur.bnogt));
 
-	/*
-	 * Got both cursors still active, need to find better entry.
-	 */
-	if (xfs_alloc_cur_active(acur.bnolt) &&
-	    xfs_alloc_cur_active(acur.bnogt)) {
-		if (ltlena >= args->minlen) {
-			/*
-			 * Left side is good, look for a right side entry.
-			 */
-			args->len = XFS_EXTLEN_MIN(ltlena, args->maxlen);
-			xfs_alloc_fix_len(args);
-			ltdiff = xfs_alloc_compute_diff(args->agbno, args->len,
-				args->alignment, args->datatype, ltbnoa,
-				ltlena, &ltnew);
-
-			error = xfs_alloc_find_best_extent(args,
-						acur.bnolt, acur.bnogt,
-						ltdiff, &gtbno, &gtlen,
-						&gtbnoa, &gtlena,
-						0 /* search right */);
-		} else {
-			ASSERT(gtlena >= args->minlen);
-
-			/*
-			 * Right side is good, look for a left side entry.
-			 */
-			args->len = XFS_EXTLEN_MIN(gtlena, args->maxlen);
-			xfs_alloc_fix_len(args);
-			gtdiff = xfs_alloc_compute_diff(args->agbno, args->len,
-				args->alignment, args->datatype, gtbnoa,
-				gtlena, &gtnew);
-
-			error = xfs_alloc_find_best_extent(args,
-						acur.bnogt, acur.bnolt,
-						gtdiff, &ltbno, &ltlen,
-						&ltbnoa, &ltlena,
-						1 /* search left */);
-		}
-
+	/* search the opposite direction for a better entry */
+	if (fbcur) {
+		error = xfs_alloc_find_best_extent(args, &acur, fbcur, fbinc);
 		if (error)
 			goto out;
 	}
@@ -1511,8 +1422,7 @@ restart:
 	/*
 	 * If we couldn't get anything, give up.
 	 */
-	if (!xfs_alloc_cur_active(acur.bnolt) &&
-	    !xfs_alloc_cur_active(acur.bnogt)) {
+	if (!acur.len) {
 		if (acur.busy) {
 			trace_xfs_alloc_near_busy(args);
 			xfs_extent_busy_flush(args->mp, args->pag,
@@ -1524,47 +1434,15 @@ restart:
 		goto out;
 	}
 
-	/*
-	 * At this point we have selected a freespace entry, either to the
-	 * left or to the right.  If it's on the right, copy all the
-	 * useful variables to the "left" set so we only have one
-	 * copy of this code.
-	 */
-	if (xfs_alloc_cur_active(acur.bnogt)) {
-		bno_cur = acur.bnogt;
-		ltbno = gtbno;
-		ltbnoa = gtbnoa;
-		ltlen = gtlen;
-		ltlena = gtlena;
-		j = 1;
-	} else {
-		bno_cur = acur.bnolt;
-		j = 0;
-	}
-
-	/*
-	 * Fix up the length and compute the useful address.
-	 */
-	args->len = XFS_EXTLEN_MIN(ltlena, args->maxlen);
-	xfs_alloc_fix_len(args);
-	rlen = args->len;
-	(void)xfs_alloc_compute_diff(args->agbno, rlen, args->alignment,
-				     args->datatype, ltbnoa, ltlena, &ltnew);
-	ASSERT(ltnew >= ltbno);
-	ASSERT(ltnew + rlen <= ltbnoa + ltlena);
-	ASSERT(ltnew + rlen <= be32_to_cpu(XFS_BUF_TO_AGF(args->agbp)->agf_length));
-	ASSERT(ltnew >= args->min_agbno && ltnew <= args->max_agbno);
-	args->agbno = ltnew;
-
-	error = xfs_alloc_fixup_trees(acur.cnt, bno_cur, ltbno, ltlen, ltnew,
-				      rlen, XFSA_FIXUP_BNO_OK);
-	if (error)
-		goto out;
+	args->agbno = acur.bno;
+	args->len = acur.len;
+	ASSERT(acur.bno >= acur.rec_bno);
+	ASSERT(acur.bno + acur.len <= acur.rec_bno + acur.rec_len);
+	ASSERT(acur.rec_bno + acur.rec_len <=
+	       be32_to_cpu(XFS_BUF_TO_AGF(args->agbp)->agf_length));
 
-	if (j)
-		trace_xfs_alloc_near_greater(args);
-	else
-		trace_xfs_alloc_near_lesser(args);
+	error = xfs_alloc_fixup_trees(acur.cnt, acur.bnolt, acur.rec_bno,
+				      acur.rec_len, acur.bno, acur.len, 0);
 
 out:
 	xfs_alloc_cur_close(&acur, error);
diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
index 61b53a30f8f2..cdc5f000d608 100644
--- a/fs/xfs/xfs_trace.h
+++ b/fs/xfs/xfs_trace.h
@@ -1577,8 +1577,8 @@ DEFINE_ALLOC_EVENT(xfs_alloc_exact_notfound);
 DEFINE_ALLOC_EVENT(xfs_alloc_exact_error);
 DEFINE_ALLOC_EVENT(xfs_alloc_near_nominleft);
 DEFINE_ALLOC_EVENT(xfs_alloc_near_first);
-DEFINE_ALLOC_EVENT(xfs_alloc_near_greater);
-DEFINE_ALLOC_EVENT(xfs_alloc_near_lesser);
+DEFINE_ALLOC_EVENT(xfs_alloc_cur_right);
+DEFINE_ALLOC_EVENT(xfs_alloc_cur_left);
 DEFINE_ALLOC_EVENT(xfs_alloc_near_error);
 DEFINE_ALLOC_EVENT(xfs_alloc_near_noentry);
 DEFINE_ALLOC_EVENT(xfs_alloc_near_busy);