xfs: introduce xfs_for_each_perag_wrap()

In several places we iterate every AG from a specific start agno and
wrap back to the first AG when we reach the end of the filesystem to
continue searching. We don't have a primitive for this iteration
yet, so add one for conversion of these algorithms to per-ag based
iteration.

The filestream AG select code is a mess, and this initially makes it
worse. The per-ag selection needs to be driven completely into the
filestream code to clean this up and it will be done in a future
patch that makes the filestream allocator use active per-ag
references correctly.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

fs/xfs/libxfs/xfs_ag.h

@@ -237,7 +237,6 @@ xfs_perag_next(
 #define for_each_perag_from(mp, agno, pag) \
 	for_each_perag_range((mp), (agno), (mp)->m_sb.sb_agcount - 1, (pag))
 
-
 #define for_each_perag(mp, agno, pag) \
 	(agno) = 0; \
 	for_each_perag_from((mp), (agno), (pag))
@@ -249,6 +248,50 @@ xfs_perag_next(
 		xfs_perag_rele(pag), \
 		(pag) = xfs_perag_grab_tag((mp), (agno), (tag)))
 
+static inline struct xfs_perag *
+xfs_perag_next_wrap(
+	struct xfs_perag	*pag,
+	xfs_agnumber_t		*agno,
+	xfs_agnumber_t		stop_agno,
+	xfs_agnumber_t		wrap_agno)
+{
+	struct xfs_mount	*mp = pag->pag_mount;
+
+	*agno = pag->pag_agno + 1;
+	xfs_perag_rele(pag);
+	while (*agno != stop_agno) {
+		if (*agno >= wrap_agno)
+			*agno = 0;
+		if (*agno == stop_agno)
+			break;
+
+		pag = xfs_perag_grab(mp, *agno);
+		if (pag)
+			return pag;
+		(*agno)++;
+	}
+	return NULL;
+}
+
+/*
+ * Iterate all AGs from start_agno through wrap_agno, then 0 through
+ * (start_agno - 1).
+ */
+#define for_each_perag_wrap_at(mp, start_agno, wrap_agno, agno, pag) \
+	for ((agno) = (start_agno), (pag) = xfs_perag_grab((mp), (agno)); \
+		(pag) != NULL; \
+		(pag) = xfs_perag_next_wrap((pag), &(agno), (start_agno), \
+				(wrap_agno)))
+
+/*
+ * Iterate all AGs from start_agno through to the end of the filesystem, then 0
+ * through (start_agno - 1).
+ */
+#define for_each_perag_wrap(mp, start_agno, agno, pag) \
+	for_each_perag_wrap_at((mp), (start_agno), (mp)->m_sb.sb_agcount, \
+				(agno), (pag))
+
+
 struct aghdr_init_data {
 	/* per ag data */
 	xfs_agblock_t		agno;		/* ag to init */

fs/xfs/libxfs/xfs_bmap.c

@@ -3136,17 +3136,14 @@ xfs_bmap_adjacent(
 
 static int
 xfs_bmap_longest_free_extent(
+	struct xfs_perag	*pag,
 	struct xfs_trans	*tp,
-	xfs_agnumber_t		ag,
 	xfs_extlen_t		*blen,
 	int			*notinit)
 {
-	struct xfs_mount	*mp = tp->t_mountp;
-	struct xfs_perag	*pag;
 	xfs_extlen_t		longest;
 	int			error = 0;
 
-	pag = xfs_perag_get(mp, ag);
 	if (!xfs_perag_initialised_agf(pag)) {
 		error = xfs_alloc_read_agf(pag, tp, XFS_ALLOC_FLAG_TRYLOCK,
 				NULL);
@@ -3156,19 +3153,17 @@ xfs_bmap_longest_free_extent(
 				*notinit = 1;
 				error = 0;
 			}
-			goto out;
+			return error;
 		}
 	}
 
 	longest = xfs_alloc_longest_free_extent(pag,
-				xfs_alloc_min_freelist(mp, pag),
+				xfs_alloc_min_freelist(pag->pag_mount, pag),
 				xfs_ag_resv_needed(pag, XFS_AG_RESV_NONE));
 	if (*blen < longest)
 		*blen = longest;
 
-out:
-	xfs_perag_put(pag);
-	return error;
+	return 0;
 }
 
 static void
@@ -3206,9 +3201,10 @@ xfs_bmap_btalloc_select_lengths(
 	xfs_extlen_t		*blen)
 {
 	struct xfs_mount	*mp = ap->ip->i_mount;
-	xfs_agnumber_t		ag, startag;
+	struct xfs_perag	*pag;
+	xfs_agnumber_t		agno, startag;
 	int			notinit = 0;
-	int			error;
+	int			error = 0;
 
 	args->type = XFS_ALLOCTYPE_START_BNO;
 	if (ap->tp->t_flags & XFS_TRANS_LOWMODE) {
@@ -3218,24 +3214,24 @@ xfs_bmap_btalloc_select_lengths(
 	}
 
 	args->total = ap->total;
-	startag = ag = XFS_FSB_TO_AGNO(mp, args->fsbno);
+	startag = XFS_FSB_TO_AGNO(mp, args->fsbno);
 	if (startag == NULLAGNUMBER)
-		startag = ag = 0;
+		startag = 0;
 
-	while (*blen < args->maxlen) {
-		error = xfs_bmap_longest_free_extent(args->tp, ag, blen,
+	*blen = 0;
+	for_each_perag_wrap(mp, startag, agno, pag) {
+		error = xfs_bmap_longest_free_extent(pag, args->tp, blen,
 						     &notinit);
 		if (error)
-			return error;
-
-		if (++ag == mp->m_sb.sb_agcount)
-			ag = 0;
-		if (ag == startag)
+			break;
+		if (*blen >= args->maxlen)
 			break;
 	}
+	if (pag)
+		xfs_perag_rele(pag);
 
 	xfs_bmap_select_minlen(ap, args, blen, notinit);
-	return 0;
+	return error;
 }
 
 STATIC int
@@ -3245,7 +3241,8 @@ xfs_bmap_btalloc_filestreams(
 	xfs_extlen_t		*blen)
 {
 	struct xfs_mount	*mp = ap->ip->i_mount;
-	xfs_agnumber_t		ag;
+	struct xfs_perag	*pag;
+	xfs_agnumber_t		start_agno;
 	int			notinit = 0;
 	int			error;
 
@@ -3259,33 +3256,50 @@ xfs_bmap_btalloc_filestreams(
 	args->type = XFS_ALLOCTYPE_NEAR_BNO;
 	args->total = ap->total;
 
-	ag = XFS_FSB_TO_AGNO(mp, args->fsbno);
-	if (ag == NULLAGNUMBER)
-		ag = 0;
+	start_agno = XFS_FSB_TO_AGNO(mp, args->fsbno);
+	if (start_agno == NULLAGNUMBER)
+		start_agno = 0;
 
-	error = xfs_bmap_longest_free_extent(args->tp, ag, blen, &notinit);
-	if (error)
-		return error;
+	pag = xfs_perag_grab(mp, start_agno);
+	if (pag) {
+		error = xfs_bmap_longest_free_extent(pag, args->tp, blen,
+				&notinit);
+		xfs_perag_rele(pag);
+		if (error)
+			return error;
+	}
 
 	if (*blen < args->maxlen) {
-		error = xfs_filestream_new_ag(ap, &ag);
+		xfs_agnumber_t	agno = start_agno;
+
+		error = xfs_filestream_new_ag(ap, &agno);
 		if (error)
 			return error;
+		if (agno == NULLAGNUMBER)
+			goto out_select;
 
-		error = xfs_bmap_longest_free_extent(args->tp, ag, blen,
-						     &notinit);
+		pag = xfs_perag_grab(mp, agno);
+		if (!pag)
+			goto out_select;
+
+		error = xfs_bmap_longest_free_extent(pag, args->tp,
+				blen, &notinit);
+		xfs_perag_rele(pag);
 		if (error)
 			return error;
 
+		start_agno = agno;
+
 	}
 
+out_select:
 	xfs_bmap_select_minlen(ap, args, blen, notinit);
 
 	/*
 	 * Set the failure fallback case to look in the selected AG as stream
 	 * may have moved.
 	 */
-	ap->blkno = args->fsbno = XFS_AGB_TO_FSB(mp, ag, 0);
+	ap->blkno = args->fsbno = XFS_AGB_TO_FSB(mp, start_agno, 0);
 	return 0;
 }
 

fs/xfs/libxfs/xfs_ialloc.c

@@ -1725,7 +1725,7 @@ xfs_dialloc(
 	bool			ok_alloc = true;
 	bool			low_space = false;
 	int			flags;
-	xfs_ino_t		ino;
+	xfs_ino_t		ino = NULLFSINO;
 
 	/*
 	 * Directories, symlinks, and regular files frequently allocate at least
@@ -1773,39 +1773,37 @@ xfs_dialloc(
 	 * or in which we can allocate some inodes.  Iterate through the
 	 * allocation groups upward, wrapping at the end.
 	 */
-	agno = start_agno;
 	flags = XFS_ALLOC_FLAG_TRYLOCK;
-	for (;;) {
-		pag = xfs_perag_grab(mp, agno);
+retry:
+	for_each_perag_wrap_at(mp, start_agno, mp->m_maxagi, agno, pag) {
 		if (xfs_dialloc_good_ag(pag, *tpp, mode, flags, ok_alloc)) {
 			error = xfs_dialloc_try_ag(pag, tpp, parent,
 					&ino, ok_alloc);
 			if (error != -EAGAIN)
 				break;
+			error = 0;
 		}
 
 		if (xfs_is_shutdown(mp)) {
 			error = -EFSCORRUPTED;
 			break;
 		}
-		if (++agno == mp->m_maxagi)
-			agno = 0;
-		if (agno == start_agno) {
-			if (!flags) {
-				error = -ENOSPC;
-				break;
-			}
+	}
+	if (pag)
+		xfs_perag_rele(pag);
+	if (error)
+		return error;
+	if (ino == NULLFSINO) {
+		if (flags) {
 			flags = 0;
 			if (low_space)
 				ok_alloc = true;
+			goto retry;
 		}
-		xfs_perag_rele(pag);
+		return -ENOSPC;
 	}
-
-	if (!error)
-		*new_ino = ino;
-	xfs_perag_rele(pag);
-	return error;
+	*new_ino = ino;
+	return 0;
 }
 
 /*