xfs: replace i_pin_wait with a bit waitqueue

Replace i_pin_wait, which is only used during synchronous inode flushing
with a bit waitqueue.  This trades off a much smaller inode against
slightly slower wakeup performance, and saves 12 (32-bit) or 20 (64-bit)
bytes in the XFS inode.

Reviewed-by: Alex Elder <aelder@sgi.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ben Myers <bpm@sgi.com>

4 files changed, 24 insertions, 9 deletions

diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index eeb60d31b086..62603369b523 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -2037,7 +2037,7 @@ xfs_idestroy_fork(
  * once someone is waiting for it to be unpinned.
  */
 static void
-xfs_iunpin_nowait(
+xfs_iunpin(
         struct xfs_inode        *ip)
 {
         ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL|XFS_ILOCK_SHARED));
@@ -2049,14 +2049,29 @@ xfs_iunpin_nowait(
 
 }
 
+static void
+__xfs_iunpin_wait(
+        struct xfs_inode        *ip)
+{
+        wait_queue_head_t *wq = bit_waitqueue(&ip->i_flags, __XFS_IPINNED_BIT);
+        DEFINE_WAIT_BIT(wait, &ip->i_flags, __XFS_IPINNED_BIT);
+
+        xfs_iunpin(ip);
+
+        do {
+                prepare_to_wait(wq, &wait.wait, TASK_UNINTERRUPTIBLE);
+                if (xfs_ipincount(ip))
+                        io_schedule();
+        } while (xfs_ipincount(ip));
+        finish_wait(wq, &wait.wait);
+}
+
 void
 xfs_iunpin_wait(
         struct xfs_inode        *ip)
 {
-        if (xfs_ipincount(ip)) {
-                xfs_iunpin_nowait(ip);
-                wait_event(ip->i_ipin_wait, (xfs_ipincount(ip) == 0));
-        }
+        if (xfs_ipincount(ip))
+                __xfs_iunpin_wait(ip);
 }
 
 /*
@@ -2415,7 +2430,7 @@ xfs_iflush(
          * out for us if they occur after the log force completes.
          */
         if (!(flags & SYNC_WAIT) && xfs_ipincount(ip)) {
-                xfs_iunpin_nowait(ip);
+                xfs_iunpin(ip);
                 xfs_ifunlock(ip);
                 return EAGAIN;
         }
diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index 960d2a89b3ac..4acbe740be46 100644
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -238,7 +238,6 @@ typedef struct xfs_inode {
         mrlock_t                i_lock;         /* inode lock */
         mrlock_t                i_iolock;       /* inode IO lock */
         atomic_t                i_pincount;     /* inode pin count */
-        wait_queue_head_t       i_ipin_wait;    /* inode pinning wait queue */
         spinlock_t              i_flags_lock;   /* inode i_flags lock */
         /* Miscellaneous state. */
         unsigned long           i_flags;        /* see defined flags below */
@@ -367,6 +366,8 @@ xfs_set_projid(struct xfs_inode *ip,
 #define XFS_IDIRTY_RELEASE      (1 << 6) /* dirty release already seen */
 #define __XFS_IFLOCK_BIT        7        /* inode is being flushed right now */
 #define XFS_IFLOCK              (1 << __XFS_IFLOCK_BIT)
+#define __XFS_IPINNED_BIT       8        /* wakeup key for zero pin count */
+#define XFS_IPINNED             (1 << __XFS_IPINNED_BIT)
 
 /*
  * Per-lifetime flags need to be reset when re-using a reclaimable inode during
diff --git a/fs/xfs/xfs_inode_item.c b/fs/xfs/xfs_inode_item.c
index c8d4ce0efd5a..91d71dcd4852 100644
--- a/fs/xfs/xfs_inode_item.c
+++ b/fs/xfs/xfs_inode_item.c
@@ -555,7 +555,7 @@ xfs_inode_item_unpin(
         trace_xfs_inode_unpin(ip, _RET_IP_);
         ASSERT(atomic_read(&ip->i_pincount) > 0);
         if (atomic_dec_and_test(&ip->i_pincount))
-                wake_up(&ip->i_ipin_wait);
+                wake_up_bit(&ip->i_flags, __XFS_IPINNED_BIT);
 }
 
 /*
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 6851fa7b1afa..ee5b695c99a7 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -828,7 +828,6 @@ xfs_fs_inode_init_once(
         /* xfs inode */
         atomic_set(&ip->i_pincount, 0);
         spin_lock_init(&ip->i_flags_lock);
-        init_waitqueue_head(&ip->i_ipin_wait);
 
         mrlock_init(&ip->i_lock, MRLOCK_ALLOW_EQUAL_PRI|MRLOCK_BARRIER,
                      "xfsino", ip->i_ino);