[PATCH, RFC] xfs: take indirect blocks into accounting when selecting an AG

[Christoph Hellwig <hch@lst.de>]

We need to make sure that the indirect blocks (e.g. bmap btree blocks)
can be allocated from the same AG [1] when comitting to an AG for a
file data block allocation.  To do that we calculate the worst possible
indirect len and subtract that from the free space in the AG.

I don't really like how this makes the space allocator call back into
the bmap code (even if only for a trivial helper), but I can't think
of a better idea.

[1] strictly speaking the same AG or one with a higher AG number, but
that is so incredibly hard to express that we settle for the same AG.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/xfs/libxfs/xfs_alloc.c |  7 ++++++-
 fs/xfs/libxfs/xfs_bmap.c  | 17 +++++++++++------
 fs/xfs/libxfs/xfs_bmap.h  |  5 +++++
 3 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
index effb64c..037cbd8 100644
--- a/fs/xfs/libxfs/xfs_alloc.c
+++ b/fs/xfs/libxfs/xfs_alloc.c
@@ -38,6 +38,7 @@
 #include "xfs_buf_item.h"
 #include "xfs_log.h"
 #include "xfs_ag_resv.h"
+#include "xfs_bmap.h"
 
 struct workqueue_struct *xfs_alloc_wq;
 
@@ -2058,6 +2059,7 @@ xfs_alloc_space_available(
 	struct xfs_perag	*pag = args->pag;
 	xfs_extlen_t		longest;
 	xfs_extlen_t		reservation; /* blocks that are still reserved */
+	xfs_extlen_t		indlen = 0;
 	int			available;
 
 	if (flags & XFS_ALLOC_FLAG_FREEING)
@@ -2071,9 +2073,12 @@ xfs_alloc_space_available(
 	if ((args->minlen + args->alignment + args->minalignslop - 1) > longest)
 		return false;
 
+	if (xfs_alloc_is_userdata(args->datatype))
+		indlen = __xfs_bmap_worst_indlen(args->mp, max(args->minlen, args->maxlen));
+
 	/* do we have enough free space remaining for the allocation? */
 	available = (int)(pag->pagf_freeblks + pag->pagf_flcount -
-			  reservation - min_free - args->total);
+			  reservation - min_free - indlen - args->total);
 	if (available < (int)args->minleft || available <= 0)
 		return false;
 
diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index 266f641..b52a32d 100644
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -183,19 +183,16 @@ xfs_bmbt_update(
  * Compute the worst-case number of indirect blocks that will be used
  * for ip's delayed extent of length "len".
  */
-STATIC xfs_filblks_t
-xfs_bmap_worst_indlen(
-	xfs_inode_t	*ip,		/* incore inode pointer */
+xfs_filblks_t
+__xfs_bmap_worst_indlen(
+	xfs_mount_t	*mp,		/* mount structure */
 	xfs_filblks_t	len)		/* delayed extent length */
 {
 	int		level;		/* btree level number */
 	int		maxrecs;	/* maximum record count at this level */
-	xfs_mount_t	*mp;		/* mount structure */
 	xfs_filblks_t	rval;		/* return value */
 	xfs_filblks_t   orig_len;
 
-	mp = ip->i_mount;
-
 	/* Calculate the worst-case size of the bmbt. */
 	orig_len = len;
 	maxrecs = mp->m_bmap_dmxr[0];
@@ -222,6 +219,14 @@ xfs_bmap_worst_indlen(
 	return rval;
 }
 
+STATIC xfs_filblks_t
+xfs_bmap_worst_indlen(
+	xfs_inode_t	*ip,		/* incore inode pointer */
+	xfs_filblks_t	len)		/* delayed extent length */
+{
+	return __xfs_bmap_worst_indlen(ip->i_mount, len);
+}
+
 /*
  * Calculate the default attribute fork offset for newly created inodes.
  */
diff --git a/fs/xfs/libxfs/xfs_bmap.h b/fs/xfs/libxfs/xfs_bmap.h
index cecd094..aa2964a 100644
--- a/fs/xfs/libxfs/xfs_bmap.h
+++ b/fs/xfs/libxfs/xfs_bmap.h
@@ -263,4 +263,9 @@ int	xfs_bmap_map_extent(struct xfs_mount *mp, struct xfs_defer_ops *dfops,
 int	xfs_bmap_unmap_extent(struct xfs_mount *mp, struct xfs_defer_ops *dfops,
 		struct xfs_inode *ip, struct xfs_bmbt_irec *imap);
 
+xfs_filblks_t
+__xfs_bmap_worst_indlen(
+	xfs_mount_t	*mp,		/* mount structure */
+	xfs_filblks_t	len);		/* delayed extent length */
+
 #endif	/* __XFS_BMAP_H__ */
-- 
2.1.4