xfs: track best extent from cntbt lastblock scan in alloc cursor

If the size lookup lands in the last block of the by-size btree, the
near mode algorithm scans the entire block for the extent with best
available locality. In preparation for similar best available
extent tracking across both btrees, extend the allocation cursor
with best extent data and lift the associated state from the cntbt
last block scan code. No functional changes.
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>

fs/xfs/libxfs/xfs_alloc.c

@@ -716,6 +716,11 @@ struct xfs_alloc_cur {
 	struct xfs_btree_cur		*cnt;	/* btree cursors */
 	struct xfs_btree_cur		*bnolt;
 	struct xfs_btree_cur		*bnogt;
+	xfs_agblock_t			rec_bno;/* extent startblock */
+	xfs_extlen_t			rec_len;/* extent length */
+	xfs_agblock_t			bno;	/* alloc bno */
+	xfs_extlen_t			len;	/* alloc len */
+	xfs_extlen_t			diff;	/* diff from search bno */
 	unsigned int			busy_gen;/* busy state */
 	bool				busy;
 };
@@ -735,6 +740,11 @@ xfs_alloc_cur_setup(
 
 	ASSERT(args->alignment == 1 || args->type != XFS_ALLOCTYPE_THIS_BNO);
 
+	acur->rec_bno = 0;
+	acur->rec_len = 0;
+	acur->bno = 0;
+	acur->len = 0;
+	acur->diff = 0;
 	acur->busy = false;
 	acur->busy_gen = 0;
 
@@ -1247,10 +1257,7 @@ xfs_alloc_ag_vextent_near(
 	 * but we never loop back to the top.
 	 */
 	while (xfs_btree_islastblock(acur.cnt, 0)) {
-		xfs_extlen_t	bdiff;
-		int		besti=0;
-		xfs_extlen_t	blen=0;
-		xfs_agblock_t	bnew=0;
+		xfs_extlen_t	diff;
 
 #ifdef DEBUG
 		if (dofirst)
@@ -1281,8 +1288,8 @@ xfs_alloc_ag_vextent_near(
 				break;
 		}
 		i = acur.cnt->bc_ptrs[0];
-		for (j = 1, blen = 0, bdiff = 0;
-		     !error && j && (blen < args->maxlen || bdiff > 0);
+		for (j = 1;
+		     !error && j && (acur.len < args->maxlen || acur.diff > 0);
 		     error = xfs_btree_increment(acur.cnt, 0, &j)) {
 			/*
 			 * For each entry, decide if it's better than
@@ -1301,44 +1308,40 @@ xfs_alloc_ag_vextent_near(
 			args->len = XFS_EXTLEN_MIN(ltlena, args->maxlen);
 			xfs_alloc_fix_len(args);
 			ASSERT(args->len >= args->minlen);
-			if (args->len < blen)
+			if (args->len < acur.len)
 				continue;
-			ltdiff = xfs_alloc_compute_diff(args->agbno, args->len,
+			diff = xfs_alloc_compute_diff(args->agbno, args->len,
 				args->alignment, args->datatype, ltbnoa,
 				ltlena, &ltnew);
 			if (ltnew != NULLAGBLOCK &&
-			    (args->len > blen || ltdiff < bdiff)) {
-				bdiff = ltdiff;
-				bnew = ltnew;
-				blen = args->len;
-				besti = acur.cnt->bc_ptrs[0];
+			    (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
 		 * there's a good record somewhere, so try again.
 		 */
-		if (blen == 0)
+		if (acur.len == 0)
 			break;
-		/*
-		 * Point at the best entry, and retrieve it again.
-		 */
-		acur.cnt->bc_ptrs[0] = besti;
-		error = xfs_alloc_get_rec(acur.cnt, &ltbno, &ltlen, &i);
-		if (error)
-			goto out;
-		XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, out);
-		ASSERT(ltbno + ltlen <= be32_to_cpu(XFS_BUF_TO_AGF(args->agbp)->agf_length));
-		args->len = blen;
 
 		/*
-		 * We are allocating starting at bnew for blen blocks.
+		 * Allocate at the bno/len tracked in the cursor.
 		 */
-		args->agbno = bnew;
-		ASSERT(bnew >= ltbno);
-		ASSERT(bnew + blen <= ltbno + ltlen);
-		error = xfs_alloc_fixup_trees(acur.cnt, acur.bnolt, ltbno,
-					ltlen, bnew, blen, XFSA_FIXUP_CNT_OK);
+		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));
+
+		error = xfs_alloc_fixup_trees(acur.cnt, acur.bnolt,
+				acur.rec_bno, acur.rec_len, acur.bno, acur.len,
+				0);
 		if (error)
 			goto out;
 		trace_xfs_alloc_near_first(args);