[PATCH 4/8] XFS: Allow 64 bit machines to avoid the AIL lock during flushes

[Dave Chinner <david@xxxxxxxxxxxxx>]

When copying lsn's from the log item to the inode or dquot
flush lsn, we currently grab the AIL lock. We do this because the
LSN is a 64 bit quantity and it needs to be read atomically.
The lock is used to guarantee atomicity for 32 bit platforms.

Make the LSN copying a small function, and make the function
used conditional on BITS_PER_LONG so that 64 bit machines don't
need to take the AIL lock in these places.

Signed-off-by: Dave Chinner <david@xxxxxxxxxxxxx>
---
 fs/xfs/quota/xfs_dquot.c |    6 ++----
 fs/xfs/xfs_inode.c       |   17 +++++++----------
 fs/xfs/xfs_trans_priv.h  |   23 +++++++++++++++++++++++
 3 files changed, 32 insertions(+), 14 deletions(-)

diff --git a/fs/xfs/quota/xfs_dquot.c b/fs/xfs/quota/xfs_dquot.c
index d3f4fbb..560c072 100644
--- a/fs/xfs/quota/xfs_dquot.c
+++ b/fs/xfs/quota/xfs_dquot.c
@@ -1274,10 +1274,8 @@ xfs_qm_dqflush(
        dqp->dq_flags &= ~(XFS_DQ_DIRTY);
        mp = dqp->q_mount;
 
-       /* lsn is 64 bits */
-       spin_lock(&mp->m_ail_lock);
-       dqp->q_logitem.qli_flush_lsn = dqp->q_logitem.qli_item.li_lsn;
-       spin_unlock(&mp->m_ail_lock);
+       xfs_trans_ail_copy_lsn(mp->m_ail, &dqp->q_logitem.qli_flush_lsn,
+                                       &dqp->q_logitem.qli_item.li_lsn);
 
        /*
         * Attach an iodone routine so that we can remove this dquot from the
diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index 456941e..58a80ae 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -2213,9 +2213,9 @@ xfs_ifree_cluster(
                                iip = (xfs_inode_log_item_t *)lip;
                                ASSERT(iip->ili_logged == 1);
                                lip->li_cb = 
(void(*)(xfs_buf_t*,xfs_log_item_t*)) xfs_istale_done;
-                               spin_lock(&mp->m_ail_lock);
-                               iip->ili_flush_lsn = iip->ili_item.li_lsn;
-                               spin_unlock(&mp->m_ail_lock);
+                               xfs_trans_ail_copy_lsn(mp->m_ail,
+                                                       &iip->ili_flush_lsn,
+                                                       &iip->ili_item.li_lsn);
                                xfs_iflags_set(iip->ili_inode, XFS_ISTALE);
                                pre_flushed++;
                        }
@@ -2236,9 +2236,8 @@ xfs_ifree_cluster(
                        iip->ili_last_fields = iip->ili_format.ilf_fields;
                        iip->ili_format.ilf_fields = 0;
                        iip->ili_logged = 1;
-                       spin_lock(&mp->m_ail_lock);
-                       iip->ili_flush_lsn = iip->ili_item.li_lsn;
-                       spin_unlock(&mp->m_ail_lock);
+                       xfs_trans_ail_copy_lsn(mp->m_ail, &iip->ili_flush_lsn,
+                                               &iip->ili_item.li_lsn);
 
                        xfs_buf_attach_iodone(bp,
                                (void(*)(xfs_buf_t*,xfs_log_item_t*))
@@ -3479,10 +3478,8 @@ xfs_iflush_int(
                iip->ili_format.ilf_fields = 0;
                iip->ili_logged = 1;
 
-               ASSERT(sizeof(xfs_lsn_t) == 8); /* don't lock if it shrinks */
-               spin_lock(&mp->m_ail_lock);
-               iip->ili_flush_lsn = iip->ili_item.li_lsn;
-               spin_unlock(&mp->m_ail_lock);
+               xfs_trans_ail_copy_lsn(mp->m_ail, &iip->ili_flush_lsn,
+                                       &iip->ili_item.li_lsn);
 
                /*
                 * Attach the function xfs_iflush_done to the inode's
diff --git a/fs/xfs/xfs_trans_priv.h b/fs/xfs/xfs_trans_priv.h
index aa58535..708cff7 100644
--- a/fs/xfs/xfs_trans_priv.h
+++ b/fs/xfs/xfs_trans_priv.h
@@ -106,4 +106,27 @@ void       xfsaild_wakeup(struct xfs_ail *, xfs_lsn_t);
 int    xfsaild_start(struct xfs_ail *);
 void   xfsaild_stop(struct xfs_ail *);
 
+#if BITS_PER_LONG != 64
+static inline void
+xfs_trans_ail_copy_lsn(
+       struct xfs_ail  *ailp,
+       xfs_lsn_t       *dst,
+       xfs_lsn_t       *src)
+{
+       ASSERT(sizeof(xfs_lsn_t) == 8); /* don't lock if it shrinks */
+       spin_lock(&ailp->xa_mount->m_ail_lock);
+       *dst = *src;
+       spin_unlock(&ailp->xa_mount->m_ail_lock);
+}
+#else
+static inline void
+xfs_trans_ail_copy_lsn(
+       struct xfs_ail  *ailp,
+       xfs_lsn_t       *dst,
+       xfs_lsn_t       *src)
+{
+       ASSERT(sizeof(xfs_lsn_t) == 8);
+       *dst = *src;
+}
+#endif
 #endif /* __XFS_TRANS_PRIV_H__ */
-- 
1.5.6.5