xfs: reduce stack usage in xfs_bmap_btalloc()

diff -urpN linux-2.6-xfs1/fs/xfs/xfs_bmap.c linux-2.6-xfs1.stk1/fs/xfs/xfs_bmap.c
@@ -2648,26 +2648,18 @@ xfs_bmap_rtalloc(
 }
 
 STATIC int
-xfs_bmap_btalloc(
-	xfs_bmalloca_t	*ap)		/* bmap alloc argument struct */
+xfs_bmap_btalloc_helper(
+	xfs_bmalloca_t	*ap,		/* bmap alloc argument struct */
+	xfs_alloc_arg_t	*argsp,
+	xfs_extlen_t	*blenp)
 {
+#define args (*argsp)
+#define blen (*blenp)
 	xfs_mount_t	*mp;		/* mount point structure */
-	xfs_alloctype_t	atype = 0;	/* type for allocation routines */
 	xfs_extlen_t	align;		/* minimum allocation alignment */
 	xfs_agnumber_t	ag;
 	xfs_agnumber_t	fb_agno;	/* ag number of ap->firstblock */
-	xfs_agnumber_t	startag;
-	xfs_alloc_arg_t	args;
-	xfs_extlen_t	blen;
-	xfs_extlen_t	delta;
-	xfs_extlen_t	longest;
-	xfs_extlen_t	need;
-	xfs_extlen_t	nextminlen = 0;
-	xfs_perag_t	*pag;
 	int		nullfb;		/* true if ap->firstblock isn't set */
-	int		isaligned;
-	int		notinit;
-	int		tryagain;
 	int		error;
 
 	mp = ap->ip->i_mount;

@@ -2705,7 +2697,6 @@ xfs_bmap_btalloc(
 	/*
 	 * Normal allocation, done through xfs_alloc_vextent.
 	 */
-	tryagain = isaligned = 0;
 	args.tp = ap->tp;
 	args.mp = mp;
 	args.fsbno = ap->rval;

@@ -2713,6 +2704,9 @@ xfs_bmap_btalloc(
 	args.firstblock = ap->firstblock;
 	blen = 0;
 	if (nullfb) {
+		xfs_agnumber_t	startag;
+		int		notinit;
+
 		if (ap->userdata && xfs_inode_is_filestream(ap->ip))
 			args.type = XFS_ALLOCTYPE_NEAR_BNO;
 		else

@@ -2732,6 +2726,8 @@ xfs_bmap_btalloc(
 		notinit = 0;
 		down_read(&mp->m_peraglock);
 		while (blen < ap->alen) {
+			xfs_perag_t	*pag;
+
 			pag = &mp->m_perag[ag];
 			if (!pag->pagf_init &&
 			    (error = xfs_alloc_pagf_init(mp, args.tp,

@@ -2743,6 +2739,10 @@ xfs_bmap_btalloc(
 			 * See xfs_alloc_fix_freelist...
 			 */
 			if (pag->pagf_init) {
+				xfs_extlen_t	need;
+				xfs_extlen_t	delta;
+				xfs_extlen_t	longest;
+
 				need = XFS_MIN_FREELIST_PAG(pag, mp);
 				delta = need > pag->pagf_flcount ?
 					need - pag->pagf_flcount : 0;

@@ -2838,6 +2838,33 @@ xfs_bmap_btalloc(
 		if ((args.mod = (xfs_extlen_t)(do_mod(ap->off, args.prod))))
 			args.mod = (xfs_extlen_t)(args.prod - args.mod);
 	}
+
+	return 0; /* no error */
+#undef args
+#undef blen
+}
+
+STATIC int
+xfs_bmap_btalloc(
+	xfs_bmalloca_t	*ap)		/* bmap alloc argument struct */
+{
+	xfs_mount_t	*mp;		/* mount point structure */
+	xfs_alloctype_t	atype;		/* type for allocation routines */
+	xfs_alloc_arg_t	args;
+	xfs_extlen_t	blen;
+	xfs_extlen_t	nextminlen;
+	int		nullfb;		/* true if ap->firstblock isn't set */
+	int		isaligned;
+	int		tryagain;
+	int		error;
+
+	error = xfs_bmap_btalloc_helper(ap, &args, &blen);
+	if (error)
+		return error;
+
+	mp = ap->ip->i_mount;
+	nullfb = ap->firstblock == NULLFSBLOCK;
+
 	/*
 	 * If we are not low on available data blocks, and the
 	 * underlying logical volume manager is a stripe, and

@@ -2847,10 +2874,13 @@ xfs_bmap_btalloc(
 	 * is >= the stripe unit and the allocation offset is
 	 * at the end of file.
 	 */
+	atype = 0;
+	nextminlen = 0;
+	tryagain = isaligned = 0;
 	if (!ap->low && ap->aeof) {
+		atype = args.type;
 		if (!ap->off) {
 			args.alignment = mp->m_dalign;
-			atype = args.type;
 			isaligned = 1;
 			/*
 			 * Adjust for alignment

@@ -2864,7 +2894,6 @@ xfs_bmap_btalloc(
 			 * If it fails then do a near or start bno
 			 * allocation with alignment turned on.
 			 */
-			atype = args.type;
 			tryagain = 1;
 			args.type = XFS_ALLOCTYPE_THIS_BNO;
 			args.alignment = 1;

Index: linux-2.6-xfs/fs/xfs/xfs_bmap.c
===================================================================
@@ -2646,6 +2646,144 @@ xfs_bmap_rtalloc(
 	return 0;
 }
 
+STATIC void
+xfs_bmap_btalloc_fix_blen(
+	xfs_mount_t		*mp,
+	xfs_perag_t		*pag,
+	xfs_extlen_t		*blen)
+{
+	xfs_extlen_t		need, delta, longest;
+
+	need = XFS_MIN_FREELIST_PAG(pag, mp);
+	if (need > pag->pagf_flcount)
+		delta = need - pag->pagf_flcount;
+	else
+		delta = 0;
+
+	if (pag->pagf_longest > delta)
+		longest = pag->pagf_longest - delta;
+	else
+		longest = (pag->pagf_flcount > 0 ||
+			   pag->pagf_longest > 0);
+
+	if (*blen < longest)
+		*blen = longest;
+}
+
+STATIC int
+xfs_bmap_btalloc_nullfb(
+	xfs_bmalloca_t		*ap,
+	xfs_alloc_arg_t		*args,
+	xfs_extlen_t		*blen)
+{
+	xfs_mount_t		*mp = ap->ip->i_mount;
+	xfs_agnumber_t		ag, startag;
+	int			notinit = 0, error;
+
+	if (ap->userdata && xfs_inode_is_filestream(ap->ip))
+		args->type = XFS_ALLOCTYPE_NEAR_BNO;
+	else
+		args->type = XFS_ALLOCTYPE_START_BNO;
+	args->total = ap->total;
+
+	/*
+	 * Search for an allocation group with a single extent
+	 * large enough for the request.
+	 *
+	 * If one isn't found, then adjust the minimum allocation
+	 * size to the largest space found.
+	 */
+	startag = XFS_FSB_TO_AGNO(mp, args->fsbno);
+	if (startag == NULLAGNUMBER)
+		startag = 0;
+
+	ag = startag;
+	down_read(&mp->m_peraglock);
+	while (*blen < ap->alen) {
+		xfs_perag_t	*pag = &mp->m_perag[ag];
+
+		if (!pag->pagf_init) {
+			error = xfs_alloc_pagf_init(mp, args->tp, ag,
+			    			    XFS_ALLOC_FLAG_TRYLOCK);
+			if (error)
+				goto out_unlock;
+		}
+
+		/*
+		 * See xfs_alloc_fix_freelist...
+		 */
+		if (pag->pagf_init)
+			xfs_bmap_btalloc_fix_blen(mp, pag, blen);
+		else
+			notinit = 1;
+
+		if (xfs_inode_is_filestream(ap->ip)) {
+			if (*blen >= ap->alen)
+				break;
+
+			if (ap->userdata) {
+				/*
+				 * If startag is an invalid AG, we've come
+				 * here once before and xfs_filestream_new_ag
+				 * picked the best currently available.
+				 *
+				 * Don't continue looping, since we could
+				 * loop forever.
+				 */
+				if (startag == NULLAGNUMBER)
+					break;
+
+				error = xfs_filestream_new_ag(ap, &ag);
+				if (error)
+					goto out_unlock;
+
+				/* loop again to set 'blen'*/
+				startag = NULLAGNUMBER;
+				continue;
+			}
+		}
+		if (++ag == mp->m_sb.sb_agcount)
+			ag = 0;
+		if (ag == startag)
+			break;
+	}
+	up_read(&mp->m_peraglock);
+
+	/*
+	 * Since the above loop did a BUF_TRYLOCK, it is
+	 * possible that there is space for this request.
+	 */
+	if (notinit || *blen < ap->minlen)
+		args->minlen = ap->minlen;
+
+	/*
+	 * If the best seen length is less than the request
+	 * length, use the best as the minimum.
+	 */
+	else if (*blen < ap->alen)
+		args->minlen = *blen;
+
+	/*
+	 * Otherwise we've seen an extent as big as alen,
+	 * use that as the minimum.
+	 */
+	else
+		args->minlen = ap->alen;
+
+	/*
+	 * Set the failure fallback case to look in the selected AG as
+	 * the stream may have moved.
+	 */
+	if (xfs_inode_is_filestream(ap->ip))
+		ap->rval = args->fsbno = XFS_AGB_TO_FSB(mp, ag, 0);
+
+	return 0;
+
+ out_unlock:
+	up_read(&mp->m_peraglock);
+	return error;
+}
+
 STATIC int
 xfs_bmap_btalloc(
 	xfs_bmalloca_t	*ap)		/* bmap alloc argument struct */

@@ -2653,19 +2791,12 @@ xfs_bmap_btalloc(
 	xfs_mount_t	*mp;		/* mount point structure */
 	xfs_alloctype_t	atype = 0;	/* type for allocation routines */
 	xfs_extlen_t	align;		/* minimum allocation alignment */
-	xfs_agnumber_t	ag;
 	xfs_agnumber_t	fb_agno;	/* ag number of ap->firstblock */
-	xfs_agnumber_t	startag;
 	xfs_alloc_arg_t	args;
 	xfs_extlen_t	blen;
-	xfs_extlen_t	delta;
-	xfs_extlen_t	longest;
-	xfs_extlen_t	need;
 	xfs_extlen_t	nextminlen = 0;
-	xfs_perag_t	*pag;
 	int		nullfb;		/* true if ap->firstblock isn't set */
 	int		isaligned;
-	int		notinit;
 	int		tryagain;
 	int		error;
 

@@ -2682,6 +2813,8 @@ xfs_bmap_btalloc(
 	fb_agno = nullfb ? NULLAGNUMBER : XFS_FSB_TO_AGNO(mp, ap->firstblock);
 	if (nullfb) {
 		if (ap->userdata && xfs_inode_is_filestream(ap->ip)) {
+			xfs_agnumber_t	ag;
+
 			ag = xfs_filestream_lookup_ag(ap->ip);
 			ag = (ag != NULLAGNUMBER) ? ag : 0;
 			ap->rval = XFS_AGB_TO_FSB(mp, ag, 0);

@@ -2712,107 +2845,9 @@ xfs_bmap_btalloc(
 	args.firstblock = ap->firstblock;
 	blen = 0;
 	if (nullfb) {
-		if (ap->userdata && xfs_inode_is_filestream(ap->ip))
-			args.type = XFS_ALLOCTYPE_NEAR_BNO;
-		else
-			args.type = XFS_ALLOCTYPE_START_BNO;
-		args.total = ap->total;
-
-		/*
-		 * Search for an allocation group with a single extent
-		 * large enough for the request.
-		 *
-		 * If one isn't found, then adjust the minimum allocation
-		 * size to the largest space found.
-		 */
-		startag = ag = XFS_FSB_TO_AGNO(mp, args.fsbno);
-		if (startag == NULLAGNUMBER)
-			startag = ag = 0;
-		notinit = 0;
-		down_read(&mp->m_peraglock);
-		while (blen < ap->alen) {
-			pag = &mp->m_perag[ag];
-			if (!pag->pagf_init &&
-			    (error = xfs_alloc_pagf_init(mp, args.tp,
-				    ag, XFS_ALLOC_FLAG_TRYLOCK))) {
-				up_read(&mp->m_peraglock);
-				return error;
-			}
-			/*
-			 * See xfs_alloc_fix_freelist...
-			 */
-			if (pag->pagf_init) {
-				need = XFS_MIN_FREELIST_PAG(pag, mp);
-				delta = need > pag->pagf_flcount ?
-					need - pag->pagf_flcount : 0;
-				longest = (pag->pagf_longest > delta) ?
-					(pag->pagf_longest - delta) :
-					(pag->pagf_flcount > 0 ||
-					 pag->pagf_longest > 0);
-				if (blen < longest)
-					blen = longest;
-			} else
-				notinit = 1;
-
-			if (xfs_inode_is_filestream(ap->ip)) {
-				if (blen >= ap->alen)
-					break;
-
-				if (ap->userdata) {
-					/*
-					 * If startag is an invalid AG, we've
-					 * come here once before and
-					 * xfs_filestream_new_ag picked the
-					 * best currently available.
-					 *
-					 * Don't continue looping, since we
-					 * could loop forever.
-					 */
-					if (startag == NULLAGNUMBER)
-						break;
-
-					error = xfs_filestream_new_ag(ap, &ag);
-					if (error) {
-						up_read(&mp->m_peraglock);
-						return error;
-					}
-
-					/* loop again to set 'blen'*/
-					startag = NULLAGNUMBER;
-					continue;
-				}
-			}
-			if (++ag == mp->m_sb.sb_agcount)
-				ag = 0;
-			if (ag == startag)
-				break;
-		}
-		up_read(&mp->m_peraglock);
-		/*
-		 * Since the above loop did a BUF_TRYLOCK, it is
-		 * possible that there is space for this request.
-		 */
-		if (notinit || blen < ap->minlen)
-			args.minlen = ap->minlen;
-		/*
-		 * If the best seen length is less than the request
-		 * length, use the best as the minimum.
-		 */
-		else if (blen < ap->alen)
-			args.minlen = blen;
-		/*
-		 * Otherwise we've seen an extent as big as alen,
-		 * use that as the minimum.
-		 */
-		else
-			args.minlen = ap->alen;
-
-		/*
-		 * set the failure fallback case to look in the selected
-		 * AG as the stream may have moved.
-		 */
-		if (xfs_inode_is_filestream(ap->ip))
-			ap->rval = args.fsbno = XFS_AGB_TO_FSB(mp, ag, 0);
+		error = xfs_bmap_btalloc_nullfb(ap, &args, &blen);
+		if (error)
+			return error;
 	} else if (ap->low) {
 		if (xfs_inode_is_filestream(ap->ip))
 			args.type = XFS_ALLOCTYPE_FIRST_AG;