[PATCH 07/11] xfs: replace i_pin_wait with a bit waitqueue

[Christoph Hellwig <hch@xxxxxxxxxxxxx>]

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@xxxxxxx>
Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx>
Signed-off-by: Christoph Hellwig <hch@xxxxxx>

---
 fs/xfs/xfs_inode.c      |   27 +++++++++++++++++++++------
 fs/xfs/xfs_inode.h      |    3 ++-
 fs/xfs/xfs_inode_item.c |    2 +-
 fs/xfs/xfs_super.c      |    1 -
 4 files changed, 24 insertions(+), 9 deletions(-)

Index: xfs/fs/xfs/xfs_inode.c
===================================================================
--- xfs.orig/fs/xfs/xfs_inode.c 2011-11-30 12:59:08.843047205 +0100
+++ xfs/fs/xfs/xfs_inode.c      2011-11-30 12:59:10.296372665 +0100
@@ -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;
        }
Index: xfs/fs/xfs/xfs_inode.h
===================================================================
--- xfs.orig/fs/xfs/xfs_inode.h 2011-11-30 12:59:08.846380520 +0100
+++ xfs/fs/xfs/xfs_inode.h      2011-11-30 12:59:10.296372665 +0100
@@ -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
Index: xfs/fs/xfs/xfs_inode_item.c
===================================================================
--- xfs.orig/fs/xfs/xfs_inode_item.c    2011-11-30 12:59:08.846380520 +0100
+++ xfs/fs/xfs/xfs_inode_item.c 2011-11-30 12:59:10.296372665 +0100
@@ -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);
 }
 
 /*
Index: xfs/fs/xfs/xfs_super.c
===================================================================
--- xfs.orig/fs/xfs/xfs_super.c 2011-11-30 12:59:08.846380520 +0100
+++ xfs/fs/xfs/xfs_super.c      2011-11-30 12:59:10.296372665 +0100
@@ -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);