[RFC PATCH 1/2] xfs: arrange all unlinked inodes into one list

[Gao Xiang <hsiangkao@redhat.com>]

There is no need to keep old multiple short unlink inode buckets
since we have an in-memory double linked list for all unlinked
inodes.

Apart from the perspective of the necessity, the main advantage
is that the log and AGI update can be reduced since each AG has
the only one head now, which is implemented in the following patch.

Therefore, this patch applies the new way in xfs_iunlink() and
keep the old approach in xfs_iunlink_remove_inode() path as well
so inode eviction can still work properly in recovery.

Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
---
 fs/xfs/xfs_inode.c | 40 ++++++++++++++++++++--------------------
 1 file changed, 20 insertions(+), 20 deletions(-)

diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index ab288424764c..10565fa5ace4 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -33,6 +33,7 @@
 #include "xfs_symlink.h"
 #include "xfs_trans_priv.h"
 #include "xfs_log.h"
+#include "xfs_log_priv.h"
 #include "xfs_bmap_btree.h"
 #include "xfs_reflink.h"
 #include "xfs_iunlink_item.h"
@@ -1955,25 +1956,32 @@ xfs_iunlink_update_bucket(
 	struct xfs_trans	*tp,
 	xfs_agnumber_t		agno,
 	struct xfs_buf		*agibp,
-	unsigned int		bucket_index,
+	xfs_agino_t		old_agino,
 	xfs_agino_t		new_agino)
 {
+	struct xlog		*log = tp->t_mountp->m_log;
 	struct xfs_agi		*agi = agibp->b_addr;
 	xfs_agino_t		old_value;
-	int			offset;
+	unsigned int		bucket_index;
+	int                     offset;
 
 	ASSERT(xfs_verify_agino_or_null(tp->t_mountp, agno, new_agino));
 
+	bucket_index = 0;
+	/* During recovery, the old multiple bucket index can be applied */
+	if (!log || log->l_flags & XLOG_RECOVERY_NEEDED) {
+		ASSERT(old_agino != NULLAGINO);
+
+		if (be32_to_cpu(agi->agi_unlinked[0]) != old_agino)
+			bucket_index = old_agino % XFS_AGI_UNLINKED_BUCKETS;
+	}
+
 	old_value = be32_to_cpu(agi->agi_unlinked[bucket_index]);
 	trace_xfs_iunlink_update_bucket(tp->t_mountp, agno, bucket_index,
 			old_value, new_agino);
 
-	/*
-	 * We should never find the head of the list already set to the value
-	 * passed in because either we're adding or removing ourselves from the
-	 * head of the list.
-	 */
-	if (old_value == new_agino) {
+	/* check if the old agi_unlinked head is as expected */
+	if (old_value != old_agino) {
 		xfs_buf_mark_corrupt(agibp);
 		return -EFSCORRUPTED;
 	}
@@ -2001,14 +2009,13 @@ xfs_iunlink_insert_inode(
 	xfs_agino_t		agno = XFS_INO_TO_AGNO(mp, ip->i_ino);
 	xfs_agino_t		agino = XFS_INO_TO_AGINO(mp, ip->i_ino);
 	xfs_agino_t		next_agino;
-	short			bucket_index = agino % XFS_AGI_UNLINKED_BUCKETS;
 
 	/*
 	 * Get the index into the agi hash table for the list this inode will
 	 * go on.  Make sure the pointer isn't garbage and that this inode
 	 * isn't already on the list.
 	 */
-	next_agino = be32_to_cpu(agi->agi_unlinked[bucket_index]);
+	next_agino = be32_to_cpu(agi->agi_unlinked[0]);
 	if (next_agino == agino ||
 	    !xfs_verify_agino_or_null(mp, agno, next_agino)) {
 		xfs_buf_mark_corrupt(agibp);
@@ -2036,7 +2043,7 @@ xfs_iunlink_insert_inode(
 	}
 
 	/* Point the head of the list to point to this inode. */
-	return xfs_iunlink_update_bucket(tp, agno, agibp, bucket_index, agino);
+	return xfs_iunlink_update_bucket(tp, agno, agibp, next_agino, agino);
 }
 
 /*
@@ -2051,27 +2058,20 @@ xfs_iunlink_remove_inode(
 	struct xfs_inode	*ip)
 {
 	struct xfs_mount	*mp = tp->t_mountp;
-	struct xfs_agi		*agi = agibp->b_addr;
 	xfs_agino_t		agno = XFS_INO_TO_AGNO(mp, ip->i_ino);
 	xfs_agino_t		agino = XFS_INO_TO_AGINO(mp, ip->i_ino);
 	xfs_agino_t		next_agino = ip->i_next_unlinked;
-	short			bucket_index = agino % XFS_AGI_UNLINKED_BUCKETS;
 	int			error;
 
 	if (ip->i_prev_unlinked == NULLAGINO) {
 		/* remove from head of list */
-		if (be32_to_cpu(agi->agi_unlinked[bucket_index]) != agino) {
-			xfs_buf_mark_corrupt(agibp);
-			return -EFSCORRUPTED;
-		}
 		if (next_agino == agino ||
 		    !xfs_verify_agino_or_null(mp, agno, next_agino))
 			return -EFSCORRUPTED;
 
-		error = xfs_iunlink_update_bucket(tp, agno, agibp,
-					bucket_index, next_agino);
+		error = xfs_iunlink_update_bucket(tp, agno, agibp, agino, next_agino);
 		if (error)
-			return -EFSCORRUPTED;
+			return error;
 	} else {
 		/* lookup previous inode and update to point at next */
 		struct xfs_inode	*pip;
-- 
2.18.1