fs/xfs/xfs_trans_ail.c - kernel/prism - Git at Google

 /*
  * Copyright (c) 2000-2002,2005 Silicon Graphics, Inc.
  * Copyright (c) 2008 Dave Chinner
  * All Rights Reserved.
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License as
  * published by the Free Software Foundation.
  *
  * This program is distributed in the hope that it would be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write the Free Software Foundation,
  * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  */
 #include "xfs.h"
 #include "xfs_fs.h"
 #include "xfs_types.h"
 #include "xfs_log.h"
 #include "xfs_inum.h"
 #include "xfs_trans.h"
 #include "xfs_sb.h"
 #include "xfs_ag.h"
 #include "xfs_dmapi.h"
 #include "xfs_mount.h"
 #include "xfs_trans_priv.h"
 #include "xfs_error.h"

 STATIC void xfs_ail_insert(struct xfs_ail *, xfs_log_item_t *);
 STATIC xfs_log_item_t * xfs_ail_delete(struct xfs_ail *, xfs_log_item_t *);
 STATIC xfs_log_item_t * xfs_ail_min(struct xfs_ail *);
 STATIC xfs_log_item_t * xfs_ail_next(struct xfs_ail *, xfs_log_item_t *);

 #ifdef DEBUG
 STATIC void xfs_ail_check(struct xfs_ail *, xfs_log_item_t *);
 #else
 #define	xfs_ail_check(a,l)
 #endif /* DEBUG */


 /*
  * This is called by the log manager code to determine the LSN
  * of the tail of the log.  This is exactly the LSN of the first
  * item in the AIL.  If the AIL is empty, then this function
  * returns 0.
  *
  * We need the AIL lock in order to get a coherent read of the
  * lsn of the last item in the AIL.
  */
 xfs_lsn_t
 xfs_trans_ail_tail(
 	struct xfs_ail	*ailp)
 {
 	xfs_lsn_t	lsn;
 	xfs_log_item_t	*lip;

 	spin_lock(&ailp->xa_lock);
 	lip = xfs_ail_min(ailp);
 	if (lip == NULL) {
 		lsn = (xfs_lsn_t)0;
 	} else {
 		lsn = lip->li_lsn;
 	}
 	spin_unlock(&ailp->xa_lock);

 	return lsn;
 }

 /*
  * xfs_trans_push_ail
  *
  * This routine is called to move the tail of the AIL forward.  It does this by
  * trying to flush items in the AIL whose lsns are below the given
  * threshold_lsn.
  *
  * the push is run asynchronously in a separate thread, so we return the tail
  * of the log right now instead of the tail after the push. This means we will
  * either continue right away, or we will sleep waiting on the async thread to
  * do its work.
  *
  * We do this unlocked - we only need to know whether there is anything in the
  * AIL at the time we are called. We don't need to access the contents of
  * any of the objects, so the lock is not needed.
  */
 void
 xfs_trans_ail_push(
 	struct xfs_ail	*ailp,
 	xfs_lsn_t	threshold_lsn)
 {
 	xfs_log_item_t	*lip;

 	lip = xfs_ail_min(ailp);
 	if (lip && !XFS_FORCED_SHUTDOWN(ailp->xa_mount)) {
 		if (XFS_LSN_CMP(threshold_lsn, ailp->xa_target) > 0)
 			xfsaild_wakeup(ailp, threshold_lsn);
 	}
 }

 /*
  * AIL traversal cursor initialisation.
  *
  * The cursor keeps track of where our current traversal is up
  * to by tracking the next ƣtem in the list for us. However, for
  * this to be safe, removing an object from the AIL needs to invalidate
  * any cursor that points to it. hence the traversal cursor needs to
  * be linked to the struct xfs_ail so that deletion can search all the
  * active cursors for invalidation.
  *
  * We don't link the push cursor because it is embedded in the struct
  * xfs_ail and hence easily findable.
  */
 STATIC void
 xfs_trans_ail_cursor_init(
 	struct xfs_ail		*ailp,
 	struct xfs_ail_cursor	*cur)
 {
 	cur->item = NULL;
 	if (cur == &ailp->xa_cursors)
 		return;

 	cur->next = ailp->xa_cursors.next;
 	ailp->xa_cursors.next = cur;
 }

 /*
  * Set the cursor to the next item, because when we look
  * up the cursor the current item may have been freed.
  */
 STATIC void
 xfs_trans_ail_cursor_set(
 	struct xfs_ail		*ailp,
 	struct xfs_ail_cursor	*cur,
 	struct xfs_log_item	*lip)
 {
 	if (lip)
 		cur->item = xfs_ail_next(ailp, lip);
 }

 /*
  * Get the next item in the traversal and advance the cursor.
  * If the cursor was invalidated (inidicated by a lip of 1),
  * restart the traversal.
  */
 struct xfs_log_item *
 xfs_trans_ail_cursor_next(
 	struct xfs_ail		*ailp,
 	struct xfs_ail_cursor	*cur)
 {
 	struct xfs_log_item	*lip = cur->item;

 	if ((__psint_t)lip & 1)
 		lip = xfs_ail_min(ailp);
 	xfs_trans_ail_cursor_set(ailp, cur, lip);
 	return lip;
 }

 /*
  * Now that the traversal is complete, we need to remove the cursor
  * from the list of traversing cursors. Avoid removing the embedded
  * push cursor, but use the fact it is always present to make the
  * list deletion simple.
  */
 void
 xfs_trans_ail_cursor_done(
 	struct xfs_ail		*ailp,
 	struct xfs_ail_cursor	*done)
 {
 	struct xfs_ail_cursor	*prev = NULL;
 	struct xfs_ail_cursor	*cur;

 	done->item = NULL;
 	if (done == &ailp->xa_cursors)
 		return;
 	prev = &ailp->xa_cursors;
 	for (cur = prev->next; cur; prev = cur, cur = prev->next) {
 		if (cur == done) {
 			prev->next = cur->next;
 			break;
 		}
 	}
 	ASSERT(cur);
 }

 /*
  * Invalidate any cursor that is pointing to this item. This is
  * called when an item is removed from the AIL. Any cursor pointing
  * to this object is now invalid and the traversal needs to be
  * terminated so it doesn't reference a freed object. We set the
  * cursor item to a value of 1 so we can distinguish between an
  * invalidation and the end of the list when getting the next item
  * from the cursor.
  */
 STATIC void
 xfs_trans_ail_cursor_clear(
 	struct xfs_ail		*ailp,
 	struct xfs_log_item	*lip)
 {
 	struct xfs_ail_cursor	*cur;

 	/* need to search all cursors */
 	for (cur = &ailp->xa_cursors; cur; cur = cur->next) {
 		if (cur->item == lip)
 			cur->item = (struct xfs_log_item *)
 					((__psint_t)cur->item | 1);
 	}
 }

 /*
  * Return the item in the AIL with the current lsn.
  * Return the current tree generation number for use
  * in calls to xfs_trans_next_ail().
  */
 xfs_log_item_t *
 xfs_trans_ail_cursor_first(
 	struct xfs_ail		*ailp,
 	struct xfs_ail_cursor	*cur,
 	xfs_lsn_t		lsn)
 {
 	xfs_log_item_t		*lip;

 	xfs_trans_ail_cursor_init(ailp, cur);
 	lip = xfs_ail_min(ailp);
 	if (lsn == 0)
 		goto out;

 	list_for_each_entry(lip, &ailp->xa_ail, li_ail) {
 		if (XFS_LSN_CMP(lip->li_lsn, lsn) >= 0)
 			goto out;
 	}
 	lip = NULL;
 out:
 	xfs_trans_ail_cursor_set(ailp, cur, lip);
 	return lip;
 }

 /*
  * Function that does the work of pushing on the AIL
  */
 long
 xfsaild_push(
 	struct xfs_ail	*ailp,
 	xfs_lsn_t	*last_lsn)
 {
 	long		tout = 1000; /* milliseconds */
 	xfs_lsn_t	last_pushed_lsn = *last_lsn;
 	xfs_lsn_t	target =  ailp->xa_target;
 	xfs_lsn_t	lsn;
 	xfs_log_item_t	*lip;
 	int		flush_log, count, stuck;
 	xfs_mount_t	*mp = ailp->xa_mount;
 	struct xfs_ail_cursor	*cur = &ailp->xa_cursors;

 	spin_lock(&ailp->xa_lock);
 	xfs_trans_ail_cursor_init(ailp, cur);
 	lip = xfs_trans_ail_cursor_first(ailp, cur, *last_lsn);
 	if (!lip || XFS_FORCED_SHUTDOWN(mp)) {
 		/*
 		 * AIL is empty or our push has reached the end.
 		 */
 		xfs_trans_ail_cursor_done(ailp, cur);
 		spin_unlock(&ailp->xa_lock);
 		last_pushed_lsn = 0;
 		return tout;
 	}

 	XFS_STATS_INC(xs_push_ail);

 	/*
 	 * While the item we are looking at is below the given threshold
 	 * try to flush it out. We'd like not to stop until we've at least
 	 * tried to push on everything in the AIL with an LSN less than
 	 * the given threshold.
 	 *
 	 * However, we will stop after a certain number of pushes and wait
 	 * for a reduced timeout to fire before pushing further. This
 	 * prevents use from spinning when we can't do anything or there is
 	 * lots of contention on the AIL lists.
 	 */
 	tout = 10;
 	lsn = lip->li_lsn;
 	flush_log = stuck = count = 0;
 	while ((XFS_LSN_CMP(lip->li_lsn, target) < 0)) {
 		int	lock_result;
 		/*
 		 * If we can lock the item without sleeping, unlock the AIL
 		 * lock and flush the item.  Then re-grab the AIL lock so we
 		 * can look for the next item on the AIL. List changes are
 		 * handled by the AIL lookup functions internally
 		 *
 		 * If we can't lock the item, either its holder will flush it
 		 * or it is already being flushed or it is being relogged.  In
 		 * any of these case it is being taken care of and we can just
 		 * skip to the next item in the list.
 		 */
 		lock_result = IOP_TRYLOCK(lip);
 		spin_unlock(&ailp->xa_lock);
 		switch (lock_result) {
 		case XFS_ITEM_SUCCESS:
 			XFS_STATS_INC(xs_push_ail_success);
 			IOP_PUSH(lip);
 			last_pushed_lsn = lsn;
 			break;

 		case XFS_ITEM_PUSHBUF:
 			XFS_STATS_INC(xs_push_ail_pushbuf);
 			IOP_PUSHBUF(lip);
 			last_pushed_lsn = lsn;
 			break;

 		case XFS_ITEM_PINNED:
 			XFS_STATS_INC(xs_push_ail_pinned);
 			stuck++;
 			flush_log = 1;
 			break;

 		case XFS_ITEM_LOCKED:
 			XFS_STATS_INC(xs_push_ail_locked);
 			last_pushed_lsn = lsn;
 			stuck++;
 			break;

 		case XFS_ITEM_FLUSHING:
 			XFS_STATS_INC(xs_push_ail_flushing);
 			last_pushed_lsn = lsn;
 			stuck++;
 			break;

 		default:
 			ASSERT(0);
 			break;
 		}

 		spin_lock(&ailp->xa_lock);
 		/* should we bother continuing? */
 		if (XFS_FORCED_SHUTDOWN(mp))
 			break;
 		ASSERT(mp->m_log);

 		count++;

 		/*
 		 * Are there too many items we can't do anything with?
 		 * If we we are skipping too many items because we can't flush
 		 * them or they are already being flushed, we back off and
 		 * given them time to complete whatever operation is being
 		 * done. i.e. remove pressure from the AIL while we can't make
 		 * progress so traversals don't slow down further inserts and
 		 * removals to/from the AIL.
 		 *
 		 * The value of 100 is an arbitrary magic number based on
 		 * observation.
 		 */
 		if (stuck > 100)
 			break;

 		lip = xfs_trans_ail_cursor_next(ailp, cur);
 		if (lip == NULL)
 			break;
 		lsn = lip->li_lsn;
 	}
 	xfs_trans_ail_cursor_done(ailp, cur);
 	spin_unlock(&ailp->xa_lock);

 	if (flush_log) {
 		/*
 		 * If something we need to push out was pinned, then
 		 * push out the log so it will become unpinned and
 		 * move forward in the AIL.
 		 */
 		XFS_STATS_INC(xs_push_ail_flush);
 		xfs_log_force(mp, (xfs_lsn_t)0, XFS_LOG_FORCE);
 	}

 	if (!count) {
 		/* We're past our target or empty, so idle */
 		tout = 1000;
 	} else if (XFS_LSN_CMP(lsn, target) >= 0) {
 		/*
 		 * We reached the target so wait a bit longer for I/O to
 		 * complete and remove pushed items from the AIL before we
 		 * start the next scan from the start of the AIL.
 		 */
 		tout += 20;
 		last_pushed_lsn = 0;
 	} else if ((stuck * 100) / count > 90) {
 		/*
 		 * Either there is a lot of contention on the AIL or we
 		 * are stuck due to operations in progress. "Stuck" in this
 		 * case is defined as >90% of the items we tried to push
 		 * were stuck.
 		 *
 		 * Backoff a bit more to allow some I/O to complete before
 		 * continuing from where we were.
 		 */
 		tout += 10;
 	}
 	*last_lsn = last_pushed_lsn;
 	return tout;
 }	/* xfsaild_push */


 /*
  * This is to be called when an item is unlocked that may have
  * been in the AIL.  It will wake up the first member of the AIL
  * wait list if this item's unlocking might allow it to progress.
  * If the item is in the AIL, then we need to get the AIL lock
  * while doing our checking so we don't race with someone going
  * to sleep waiting for this event in xfs_trans_push_ail().
  */
 void
 xfs_trans_unlocked_item(
 	struct xfs_ail	*ailp,
 	xfs_log_item_t	*lip)
 {
 	xfs_log_item_t	*min_lip;

 	/*
 	 * If we're forcibly shutting down, we may have
 	 * unlocked log items arbitrarily. The last thing
 	 * we want to do is to move the tail of the log
 	 * over some potentially valid data.
 	 */
 	if (!(lip->li_flags & XFS_LI_IN_AIL) ||
 	    XFS_FORCED_SHUTDOWN(ailp->xa_mount)) {
 		return;
 	}

 	/*
 	 * This is the one case where we can call into xfs_ail_min()
 	 * without holding the AIL lock because we only care about the
 	 * case where we are at the tail of the AIL.  If the object isn't
 	 * at the tail, it doesn't matter what result we get back.  This
 	 * is slightly racy because since we were just unlocked, we could
 	 * go to sleep between the call to xfs_ail_min and the call to
 	 * xfs_log_move_tail, have someone else lock us, commit to us disk,
 	 * move us out of the tail of the AIL, and then we wake up.  However,
 	 * the call to xfs_log_move_tail() doesn't do anything if there's
 	 * not enough free space to wake people up so we're safe calling it.
 	 */
 	min_lip = xfs_ail_min(ailp);

 	if (min_lip == lip)
 		xfs_log_move_tail(ailp->xa_mount, 1);
 }	/* xfs_trans_unlocked_item */


 /*
  * Update the position of the item in the AIL with the new
  * lsn.  If it is not yet in the AIL, add it.  Otherwise, move
  * it to its new position by removing it and re-adding it.
  *
  * Wakeup anyone with an lsn less than the item's lsn.  If the item
  * we move in the AIL is the minimum one, update the tail lsn in the
  * log manager.
  *
  * This function must be called with the AIL lock held.  The lock
  * is dropped before returning.
  */
 void
 xfs_trans_ail_update(
 	struct xfs_ail	*ailp,
 	xfs_log_item_t	*lip,
 	xfs_lsn_t	lsn) __releases(ailp->xa_lock)
 {
 	xfs_log_item_t		*dlip = NULL;
 	xfs_log_item_t		*mlip;	/* ptr to minimum lip */
 	xfs_lsn_t		tail_lsn;

 	mlip = xfs_ail_min(ailp);

 	if (lip->li_flags & XFS_LI_IN_AIL) {
 		dlip = xfs_ail_delete(ailp, lip);
 		ASSERT(dlip == lip);
 		xfs_trans_ail_cursor_clear(ailp, dlip);
 	} else {
 		lip->li_flags |= XFS_LI_IN_AIL;
 	}

 	lip->li_lsn = lsn;
 	xfs_ail_insert(ailp, lip);

 	if (mlip == dlip) {
 		mlip = xfs_ail_min(ailp);
 		/*
 		 * It is not safe to access mlip after the AIL lock is
 		 * dropped, so we must get a copy of li_lsn before we do
 		 * so.  This is especially important on 32-bit platforms
 		 * where accessing and updating 64-bit values like li_lsn
 		 * is not atomic.
 		 */
 		tail_lsn = mlip->li_lsn;
 		spin_unlock(&ailp->xa_lock);
 		xfs_log_move_tail(ailp->xa_mount, tail_lsn);
 	} else {
 		spin_unlock(&ailp->xa_lock);
 	}


 }	/* xfs_trans_update_ail */

 /*
  * Delete the given item from the AIL.  It must already be in
  * the AIL.
  *
  * Wakeup anyone with an lsn less than item's lsn.    If the item
  * we delete in the AIL is the minimum one, update the tail lsn in the
  * log manager.
  *
  * Clear the IN_AIL flag from the item, reset its lsn to 0, and
  * bump the AIL's generation count to indicate that the tree
  * has changed.
  *
  * This function must be called with the AIL lock held.  The lock
  * is dropped before returning.
  */
 void
 xfs_trans_ail_delete(
 	struct xfs_ail	*ailp,
 	xfs_log_item_t	*lip) __releases(ailp->xa_lock)
 {
 	xfs_log_item_t		*dlip;
 	xfs_log_item_t		*mlip;
 	xfs_lsn_t		tail_lsn;

 	if (lip->li_flags & XFS_LI_IN_AIL) {
 		mlip = xfs_ail_min(ailp);
 		dlip = xfs_ail_delete(ailp, lip);
 		ASSERT(dlip == lip);
 		xfs_trans_ail_cursor_clear(ailp, dlip);


 		lip->li_flags &= ~XFS_LI_IN_AIL;
 		lip->li_lsn = 0;

 		if (mlip == dlip) {
 			mlip = xfs_ail_min(ailp);
 			/*
 			 * It is not safe to access mlip after the AIL lock
 			 * is dropped, so we must get a copy of li_lsn
 			 * before we do so.  This is especially important
 			 * on 32-bit platforms where accessing and updating
 			 * 64-bit values like li_lsn is not atomic.
 			 */
 			tail_lsn = mlip ? mlip->li_lsn : 0;
 			spin_unlock(&ailp->xa_lock);
 			xfs_log_move_tail(ailp->xa_mount, tail_lsn);
 		} else {
 			spin_unlock(&ailp->xa_lock);
 		}
 	}
 	else {
 		/*
 		 * If the file system is not being shutdown, we are in
 		 * serious trouble if we get to this stage.
 		 */
 		struct xfs_mount	*mp = ailp->xa_mount;

 		spin_unlock(&ailp->xa_lock);
 		if (!XFS_FORCED_SHUTDOWN(mp)) {
 			xfs_cmn_err(XFS_PTAG_AILDELETE, CE_ALERT, mp,
 		"%s: attempting to delete a log item that is not in the AIL",
 					__func__);
 			xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
 		}
 	}
 }


 /*
  * The active item list (AIL) is a doubly linked list of log
  * items sorted by ascending lsn.  The base of the list is
  * a forw/back pointer pair embedded in the xfs mount structure.
  * The base is initialized with both pointers pointing to the
  * base.  This case always needs to be distinguished, because
  * the base has no lsn to look at.  We almost always insert
  * at the end of the list, so on inserts we search from the
  * end of the list to find where the new item belongs.
  */

 /*
  * Initialize the doubly linked list to point only to itself.
  */
 int
 xfs_trans_ail_init(
 	xfs_mount_t	*mp)
 {
 	struct xfs_ail	*ailp;
 	int		error;

 	ailp = kmem_zalloc(sizeof(struct xfs_ail), KM_MAYFAIL);
 	if (!ailp)
 		return ENOMEM;

 	ailp->xa_mount = mp;
 	INIT_LIST_HEAD(&ailp->xa_ail);
 	spin_lock_init(&ailp->xa_lock);
 	error = xfsaild_start(ailp);
 	if (error)
 		goto out_free_ailp;
 	mp->m_ail = ailp;
 	return 0;

 out_free_ailp:
 	kmem_free(ailp);
 	return error;
 }

 void
 xfs_trans_ail_destroy(
 	xfs_mount_t	*mp)
 {
 	struct xfs_ail	*ailp = mp->m_ail;

 	xfsaild_stop(ailp);
 	kmem_free(ailp);
 }

 /*
  * Insert the given log item into the AIL.
  * We almost always insert at the end of the list, so on inserts
  * we search from the end of the list to find where the
  * new item belongs.
  */
 STATIC void
 xfs_ail_insert(
 	struct xfs_ail	*ailp,
 	xfs_log_item_t	*lip)
 /* ARGSUSED */
 {
 	xfs_log_item_t	*next_lip;

 	/*
 	 * If the list is empty, just insert the item.
 	 */
 	if (list_empty(&ailp->xa_ail)) {
 		list_add(&lip->li_ail, &ailp->xa_ail);
 		return;
 	}

 	list_for_each_entry_reverse(next_lip, &ailp->xa_ail, li_ail) {
 		if (XFS_LSN_CMP(next_lip->li_lsn, lip->li_lsn) <= 0)
 			break;
 	}

 	ASSERT((&next_lip->li_ail == &ailp->xa_ail) ||
 	       (XFS_LSN_CMP(next_lip->li_lsn, lip->li_lsn) <= 0));

 	list_add(&lip->li_ail, &next_lip->li_ail);

 	xfs_ail_check(ailp, lip);
 	return;
 }

 /*
  * Delete the given item from the AIL.  Return a pointer to the item.
  */
 /*ARGSUSED*/
 STATIC xfs_log_item_t *
 xfs_ail_delete(
 	struct xfs_ail	*ailp,
 	xfs_log_item_t	*lip)
 /* ARGSUSED */
 {
 	xfs_ail_check(ailp, lip);

 	list_del(&lip->li_ail);

 	return lip;
 }

 /*
  * Return a pointer to the first item in the AIL.
  * If the AIL is empty, then return NULL.
  */
 STATIC xfs_log_item_t *
 xfs_ail_min(
 	struct xfs_ail	*ailp)
 /* ARGSUSED */
 {
 	if (list_empty(&ailp->xa_ail))
 		return NULL;

 	return list_first_entry(&ailp->xa_ail, xfs_log_item_t, li_ail);
 }

 /*
  * Return a pointer to the item which follows
  * the given item in the AIL.  If the given item
  * is the last item in the list, then return NULL.
  */
 STATIC xfs_log_item_t *
 xfs_ail_next(
 	struct xfs_ail	*ailp,
 	xfs_log_item_t	*lip)
 /* ARGSUSED */
 {
 	if (lip->li_ail.next == &ailp->xa_ail)
 		return NULL;

 	return list_first_entry(&lip->li_ail, xfs_log_item_t, li_ail);
 }

 #ifdef DEBUG
 /*
  * Check that the list is sorted as it should be.
  */
 STATIC void
 xfs_ail_check(
 	struct xfs_ail	*ailp,
 	xfs_log_item_t	*lip)
 {
 	xfs_log_item_t	*prev_lip;

 	if (list_empty(&ailp->xa_ail))
 		return;

 	/*
 	 * Check the next and previous entries are valid.
 	 */
 	ASSERT((lip->li_flags & XFS_LI_IN_AIL) != 0);
 	prev_lip = list_entry(lip->li_ail.prev, xfs_log_item_t, li_ail);
 	if (&prev_lip->li_ail != &ailp->xa_ail)
 		ASSERT(XFS_LSN_CMP(prev_lip->li_lsn, lip->li_lsn) <= 0);

 	prev_lip = list_entry(lip->li_ail.next, xfs_log_item_t, li_ail);
 	if (&prev_lip->li_ail != &ailp->xa_ail)
 		ASSERT(XFS_LSN_CMP(prev_lip->li_lsn, lip->li_lsn) >= 0);


 #ifdef XFS_TRANS_DEBUG
 	/*
 	 * Walk the list checking lsn ordering, and that every entry has the
 	 * XFS_LI_IN_AIL flag set. This is really expensive, so only do it
 	 * when specifically debugging the transaction subsystem.
 	 */
 	prev_lip = list_entry(&ailp->xa_ail, xfs_log_item_t, li_ail);
 	list_for_each_entry(lip, &ailp->xa_ail, li_ail) {
 		if (&prev_lip->li_ail != &ailp->xa_ail)
 			ASSERT(XFS_LSN_CMP(prev_lip->li_lsn, lip->li_lsn) <= 0);
 		ASSERT((lip->li_flags & XFS_LI_IN_AIL) != 0);
 		prev_lip = lip;
 	}
 #endif /* XFS_TRANS_DEBUG */
 }
 #endif /* DEBUG */
	/*
	* Copyright (c) 2000-2002,2005 Silicon Graphics, Inc.
	* Copyright (c) 2008 Dave Chinner
	* All Rights Reserved.
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public License as
	* published by the Free Software Foundation.
	*
	* This program is distributed in the hope that it would be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program; if not, write the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
	*/
	#include "xfs.h"
	#include "xfs_fs.h"
	#include "xfs_types.h"
	#include "xfs_log.h"
	#include "xfs_inum.h"
	#include "xfs_trans.h"
	#include "xfs_sb.h"
	#include "xfs_ag.h"
	#include "xfs_dmapi.h"
	#include "xfs_mount.h"
	#include "xfs_trans_priv.h"
	#include "xfs_error.h"

	STATIC void xfs_ail_insert(struct xfs_ail , xfs_log_item_t );
	STATIC xfs_log_item_t * xfs_ail_delete(struct xfs_ail , xfs_log_item_t );
	STATIC xfs_log_item_t * xfs_ail_min(struct xfs_ail *);
	STATIC xfs_log_item_t * xfs_ail_next(struct xfs_ail , xfs_log_item_t );

	#ifdef DEBUG
	STATIC void xfs_ail_check(struct xfs_ail , xfs_log_item_t );
	#else
	#define xfs_ail_check(a,l)
	#endif /* DEBUG */


	/*
	* This is called by the log manager code to determine the LSN
	* of the tail of the log. This is exactly the LSN of the first
	* item in the AIL. If the AIL is empty, then this function
	* returns 0.
	*
	* We need the AIL lock in order to get a coherent read of the
	* lsn of the last item in the AIL.
	*/
	xfs_lsn_t
	xfs_trans_ail_tail(
	struct xfs_ail *ailp)
	{
	xfs_lsn_t lsn;
	xfs_log_item_t *lip;

	spin_lock(&ailp->xa_lock);
	lip = xfs_ail_min(ailp);
	if (lip == NULL) {
	lsn = (xfs_lsn_t)0;
	} else {
	lsn = lip->li_lsn;
	}
	spin_unlock(&ailp->xa_lock);

	return lsn;
	}

	/*
	* xfs_trans_push_ail
	*
	* This routine is called to move the tail of the AIL forward. It does this by
	* trying to flush items in the AIL whose lsns are below the given
	* threshold_lsn.
	*
	* the push is run asynchronously in a separate thread, so we return the tail
	* of the log right now instead of the tail after the push. This means we will
	* either continue right away, or we will sleep waiting on the async thread to
	* do its work.
	*
	* We do this unlocked - we only need to know whether there is anything in the
	* AIL at the time we are called. We don't need to access the contents of
	* any of the objects, so the lock is not needed.
	*/
	void
	xfs_trans_ail_push(
	struct xfs_ail *ailp,
	xfs_lsn_t threshold_lsn)
	{
	xfs_log_item_t *lip;

	lip = xfs_ail_min(ailp);
	if (lip && !XFS_FORCED_SHUTDOWN(ailp->xa_mount)) {
	if (XFS_LSN_CMP(threshold_lsn, ailp->xa_target) > 0)
	xfsaild_wakeup(ailp, threshold_lsn);
	}
	}

	/*
	* AIL traversal cursor initialisation.
	*
	* The cursor keeps track of where our current traversal is up
	* to by tracking the next ƣtem in the list for us. However, for
	* this to be safe, removing an object from the AIL needs to invalidate
	* any cursor that points to it. hence the traversal cursor needs to
	* be linked to the struct xfs_ail so that deletion can search all the
	* active cursors for invalidation.
	*
	* We don't link the push cursor because it is embedded in the struct
	* xfs_ail and hence easily findable.
	*/
	STATIC void
	xfs_trans_ail_cursor_init(
	struct xfs_ail *ailp,
	struct xfs_ail_cursor *cur)
	{
	cur->item = NULL;
	if (cur == &ailp->xa_cursors)
	return;

	cur->next = ailp->xa_cursors.next;
	ailp->xa_cursors.next = cur;
	}

	/*
	* Set the cursor to the next item, because when we look
	* up the cursor the current item may have been freed.
	*/
	STATIC void
	xfs_trans_ail_cursor_set(
	struct xfs_ail *ailp,
	struct xfs_ail_cursor *cur,
	struct xfs_log_item *lip)
	{
	if (lip)
	cur->item = xfs_ail_next(ailp, lip);
	}

	/*
	* Get the next item in the traversal and advance the cursor.
	* If the cursor was invalidated (inidicated by a lip of 1),
	* restart the traversal.
	*/
	struct xfs_log_item *
	xfs_trans_ail_cursor_next(
	struct xfs_ail *ailp,
	struct xfs_ail_cursor *cur)
	{
	struct xfs_log_item *lip = cur->item;

	if ((__psint_t)lip & 1)
	lip = xfs_ail_min(ailp);
	xfs_trans_ail_cursor_set(ailp, cur, lip);
	return lip;
	}

	/*
	* Now that the traversal is complete, we need to remove the cursor
	* from the list of traversing cursors. Avoid removing the embedded
	* push cursor, but use the fact it is always present to make the
	* list deletion simple.
	*/
	void
	xfs_trans_ail_cursor_done(
	struct xfs_ail *ailp,
	struct xfs_ail_cursor *done)
	{
	struct xfs_ail_cursor *prev = NULL;
	struct xfs_ail_cursor *cur;

	done->item = NULL;
	if (done == &ailp->xa_cursors)
	return;
	prev = &ailp->xa_cursors;
	for (cur = prev->next; cur; prev = cur, cur = prev->next) {
	if (cur == done) {
	prev->next = cur->next;
	break;
	}
	}
	ASSERT(cur);
	}

	/*
	* Invalidate any cursor that is pointing to this item. This is
	* called when an item is removed from the AIL. Any cursor pointing
	* to this object is now invalid and the traversal needs to be
	* terminated so it doesn't reference a freed object. We set the
	* cursor item to a value of 1 so we can distinguish between an
	* invalidation and the end of the list when getting the next item
	* from the cursor.
	*/
	STATIC void
	xfs_trans_ail_cursor_clear(
	struct xfs_ail *ailp,
	struct xfs_log_item *lip)
	{
	struct xfs_ail_cursor *cur;

	/* need to search all cursors */
	for (cur = &ailp->xa_cursors; cur; cur = cur->next) {
	if (cur->item == lip)
	cur->item = (struct xfs_log_item *)
	((__psint_t)cur->item \| 1);
	}
	}

	/*
	* Return the item in the AIL with the current lsn.
	* Return the current tree generation number for use
	* in calls to xfs_trans_next_ail().
	*/
	xfs_log_item_t *
	xfs_trans_ail_cursor_first(
	struct xfs_ail *ailp,
	struct xfs_ail_cursor *cur,
	xfs_lsn_t lsn)
	{
	xfs_log_item_t *lip;

	xfs_trans_ail_cursor_init(ailp, cur);
	lip = xfs_ail_min(ailp);
	if (lsn == 0)
	goto out;

	list_for_each_entry(lip, &ailp->xa_ail, li_ail) {
	if (XFS_LSN_CMP(lip->li_lsn, lsn) >= 0)
	goto out;
	}
	lip = NULL;
	out:
	xfs_trans_ail_cursor_set(ailp, cur, lip);
	return lip;
	}

	/*
	* Function that does the work of pushing on the AIL
	*/
	long
	xfsaild_push(
	struct xfs_ail *ailp,
	xfs_lsn_t *last_lsn)
	{
	long tout = 1000; /* milliseconds */
	xfs_lsn_t last_pushed_lsn = *last_lsn;
	xfs_lsn_t target = ailp->xa_target;
	xfs_lsn_t lsn;
	xfs_log_item_t *lip;
	int flush_log, count, stuck;
	xfs_mount_t *mp = ailp->xa_mount;
	struct xfs_ail_cursor *cur = &ailp->xa_cursors;

	spin_lock(&ailp->xa_lock);
	xfs_trans_ail_cursor_init(ailp, cur);
	lip = xfs_trans_ail_cursor_first(ailp, cur, *last_lsn);
	if (!lip \|\| XFS_FORCED_SHUTDOWN(mp)) {
	/*
	* AIL is empty or our push has reached the end.
	*/
	xfs_trans_ail_cursor_done(ailp, cur);
	spin_unlock(&ailp->xa_lock);
	last_pushed_lsn = 0;
	return tout;
	}

	XFS_STATS_INC(xs_push_ail);

	/*
	* While the item we are looking at is below the given threshold
	* try to flush it out. We'd like not to stop until we've at least
	* tried to push on everything in the AIL with an LSN less than
	* the given threshold.
	*
	* However, we will stop after a certain number of pushes and wait
	* for a reduced timeout to fire before pushing further. This
	* prevents use from spinning when we can't do anything or there is
	* lots of contention on the AIL lists.
	*/
	tout = 10;
	lsn = lip->li_lsn;
	flush_log = stuck = count = 0;
	while ((XFS_LSN_CMP(lip->li_lsn, target) < 0)) {
	int lock_result;
	/*
	* If we can lock the item without sleeping, unlock the AIL
	* lock and flush the item. Then re-grab the AIL lock so we
	* can look for the next item on the AIL. List changes are
	* handled by the AIL lookup functions internally
	*
	* If we can't lock the item, either its holder will flush it
	* or it is already being flushed or it is being relogged. In
	* any of these case it is being taken care of and we can just
	* skip to the next item in the list.
	*/
	lock_result = IOP_TRYLOCK(lip);
	spin_unlock(&ailp->xa_lock);
	switch (lock_result) {
	case XFS_ITEM_SUCCESS:
	XFS_STATS_INC(xs_push_ail_success);
	IOP_PUSH(lip);
	last_pushed_lsn = lsn;
	break;

	case XFS_ITEM_PUSHBUF:
	XFS_STATS_INC(xs_push_ail_pushbuf);
	IOP_PUSHBUF(lip);
	last_pushed_lsn = lsn;
	break;

	case XFS_ITEM_PINNED:
	XFS_STATS_INC(xs_push_ail_pinned);
	stuck++;
	flush_log = 1;
	break;

	case XFS_ITEM_LOCKED:
	XFS_STATS_INC(xs_push_ail_locked);
	last_pushed_lsn = lsn;
	stuck++;
	break;

	case XFS_ITEM_FLUSHING:
	XFS_STATS_INC(xs_push_ail_flushing);
	last_pushed_lsn = lsn;
	stuck++;
	break;

	default:
	ASSERT(0);
	break;
	}

	spin_lock(&ailp->xa_lock);
	/* should we bother continuing? */
	if (XFS_FORCED_SHUTDOWN(mp))
	break;
	ASSERT(mp->m_log);

	count++;

	/*
	* Are there too many items we can't do anything with?
	* If we we are skipping too many items because we can't flush
	* them or they are already being flushed, we back off and
	* given them time to complete whatever operation is being
	* done. i.e. remove pressure from the AIL while we can't make
	* progress so traversals don't slow down further inserts and
	* removals to/from the AIL.
	*
	* The value of 100 is an arbitrary magic number based on
	* observation.
	*/
	if (stuck > 100)
	break;

	lip = xfs_trans_ail_cursor_next(ailp, cur);
	if (lip == NULL)
	break;
	lsn = lip->li_lsn;
	}
	xfs_trans_ail_cursor_done(ailp, cur);
	spin_unlock(&ailp->xa_lock);

	if (flush_log) {
	/*
	* If something we need to push out was pinned, then
	* push out the log so it will become unpinned and
	* move forward in the AIL.
	*/
	XFS_STATS_INC(xs_push_ail_flush);
	xfs_log_force(mp, (xfs_lsn_t)0, XFS_LOG_FORCE);
	}

	if (!count) {
	/* We're past our target or empty, so idle */
	tout = 1000;
	} else if (XFS_LSN_CMP(lsn, target) >= 0) {
	/*
	* We reached the target so wait a bit longer for I/O to
	* complete and remove pushed items from the AIL before we
	* start the next scan from the start of the AIL.
	*/
	tout += 20;
	last_pushed_lsn = 0;
	} else if ((stuck * 100) / count > 90) {
	/*
	* Either there is a lot of contention on the AIL or we
	* are stuck due to operations in progress. "Stuck" in this
	* case is defined as >90% of the items we tried to push
	* were stuck.
	*
	* Backoff a bit more to allow some I/O to complete before
	* continuing from where we were.
	*/
	tout += 10;
	}
	*last_lsn = last_pushed_lsn;
	return tout;
	} /* xfsaild_push */


	/*
	* This is to be called when an item is unlocked that may have
	* been in the AIL. It will wake up the first member of the AIL
	* wait list if this item's unlocking might allow it to progress.
	* If the item is in the AIL, then we need to get the AIL lock
	* while doing our checking so we don't race with someone going
	* to sleep waiting for this event in xfs_trans_push_ail().
	*/
	void
	xfs_trans_unlocked_item(
	struct xfs_ail *ailp,
	xfs_log_item_t *lip)
	{
	xfs_log_item_t *min_lip;

	/*
	* If we're forcibly shutting down, we may have
	* unlocked log items arbitrarily. The last thing
	* we want to do is to move the tail of the log
	* over some potentially valid data.
	*/
	if (!(lip->li_flags & XFS_LI_IN_AIL) \|\|
	XFS_FORCED_SHUTDOWN(ailp->xa_mount)) {
	return;
	}

	/*
	* This is the one case where we can call into xfs_ail_min()
	* without holding the AIL lock because we only care about the
	* case where we are at the tail of the AIL. If the object isn't
	* at the tail, it doesn't matter what result we get back. This
	* is slightly racy because since we were just unlocked, we could
	* go to sleep between the call to xfs_ail_min and the call to
	* xfs_log_move_tail, have someone else lock us, commit to us disk,
	* move us out of the tail of the AIL, and then we wake up. However,
	* the call to xfs_log_move_tail() doesn't do anything if there's
	* not enough free space to wake people up so we're safe calling it.
	*/
	min_lip = xfs_ail_min(ailp);

	if (min_lip == lip)
	xfs_log_move_tail(ailp->xa_mount, 1);
	} /* xfs_trans_unlocked_item */


	/*
	* Update the position of the item in the AIL with the new
	* lsn. If it is not yet in the AIL, add it. Otherwise, move
	* it to its new position by removing it and re-adding it.
	*
	* Wakeup anyone with an lsn less than the item's lsn. If the item
	* we move in the AIL is the minimum one, update the tail lsn in the
	* log manager.
	*
	* This function must be called with the AIL lock held. The lock
	* is dropped before returning.
	*/
	void
	xfs_trans_ail_update(
	struct xfs_ail *ailp,
	xfs_log_item_t *lip,
	xfs_lsn_t lsn) __releases(ailp->xa_lock)
	{
	xfs_log_item_t *dlip = NULL;
	xfs_log_item_t mlip; / ptr to minimum lip */
	xfs_lsn_t tail_lsn;

	mlip = xfs_ail_min(ailp);

	if (lip->li_flags & XFS_LI_IN_AIL) {
	dlip = xfs_ail_delete(ailp, lip);
	ASSERT(dlip == lip);
	xfs_trans_ail_cursor_clear(ailp, dlip);
	} else {
	lip->li_flags \|= XFS_LI_IN_AIL;
	}

	lip->li_lsn = lsn;
	xfs_ail_insert(ailp, lip);

	if (mlip == dlip) {
	mlip = xfs_ail_min(ailp);
	/*
	* It is not safe to access mlip after the AIL lock is
	* dropped, so we must get a copy of li_lsn before we do
	* so. This is especially important on 32-bit platforms
	* where accessing and updating 64-bit values like li_lsn
	* is not atomic.
	*/
	tail_lsn = mlip->li_lsn;
	spin_unlock(&ailp->xa_lock);
	xfs_log_move_tail(ailp->xa_mount, tail_lsn);
	} else {
	spin_unlock(&ailp->xa_lock);
	}


	} /* xfs_trans_update_ail */

	/*
	* Delete the given item from the AIL. It must already be in
	* the AIL.
	*
	* Wakeup anyone with an lsn less than item's lsn. If the item
	* we delete in the AIL is the minimum one, update the tail lsn in the
	* log manager.
	*
	* Clear the IN_AIL flag from the item, reset its lsn to 0, and
	* bump the AIL's generation count to indicate that the tree
	* has changed.
	*
	* This function must be called with the AIL lock held. The lock
	* is dropped before returning.
	*/
	void
	xfs_trans_ail_delete(
	struct xfs_ail *ailp,
	xfs_log_item_t *lip) __releases(ailp->xa_lock)
	{
	xfs_log_item_t *dlip;
	xfs_log_item_t *mlip;
	xfs_lsn_t tail_lsn;

	if (lip->li_flags & XFS_LI_IN_AIL) {
	mlip = xfs_ail_min(ailp);
	dlip = xfs_ail_delete(ailp, lip);
	ASSERT(dlip == lip);
	xfs_trans_ail_cursor_clear(ailp, dlip);


	lip->li_flags &= ~XFS_LI_IN_AIL;
	lip->li_lsn = 0;

	if (mlip == dlip) {
	mlip = xfs_ail_min(ailp);
	/*
	* It is not safe to access mlip after the AIL lock
	* is dropped, so we must get a copy of li_lsn
	* before we do so. This is especially important
	* on 32-bit platforms where accessing and updating
	* 64-bit values like li_lsn is not atomic.
	*/
	tail_lsn = mlip ? mlip->li_lsn : 0;
	spin_unlock(&ailp->xa_lock);
	xfs_log_move_tail(ailp->xa_mount, tail_lsn);
	} else {
	spin_unlock(&ailp->xa_lock);
	}
	}
	else {
	/*
	* If the file system is not being shutdown, we are in
	* serious trouble if we get to this stage.
	*/
	struct xfs_mount *mp = ailp->xa_mount;

	spin_unlock(&ailp->xa_lock);
	if (!XFS_FORCED_SHUTDOWN(mp)) {
	xfs_cmn_err(XFS_PTAG_AILDELETE, CE_ALERT, mp,
	"%s: attempting to delete a log item that is not in the AIL",
	__func__);
	xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
	}
	}
	}



	/*
	* The active item list (AIL) is a doubly linked list of log
	* items sorted by ascending lsn. The base of the list is
	* a forw/back pointer pair embedded in the xfs mount structure.
	* The base is initialized with both pointers pointing to the
	* base. This case always needs to be distinguished, because
	* the base has no lsn to look at. We almost always insert
	* at the end of the list, so on inserts we search from the
	* end of the list to find where the new item belongs.
	*/

	/*
	* Initialize the doubly linked list to point only to itself.
	*/
	int
	xfs_trans_ail_init(
	xfs_mount_t *mp)
	{
	struct xfs_ail *ailp;
	int error;

	ailp = kmem_zalloc(sizeof(struct xfs_ail), KM_MAYFAIL);
	if (!ailp)
	return ENOMEM;

	ailp->xa_mount = mp;
	INIT_LIST_HEAD(&ailp->xa_ail);
	spin_lock_init(&ailp->xa_lock);
	error = xfsaild_start(ailp);
	if (error)
	goto out_free_ailp;
	mp->m_ail = ailp;
	return 0;

	out_free_ailp:
	kmem_free(ailp);
	return error;
	}

	void
	xfs_trans_ail_destroy(
	xfs_mount_t *mp)
	{
	struct xfs_ail *ailp = mp->m_ail;

	xfsaild_stop(ailp);
	kmem_free(ailp);
	}

	/*
	* Insert the given log item into the AIL.
	* We almost always insert at the end of the list, so on inserts
	* we search from the end of the list to find where the
	* new item belongs.
	*/
	STATIC void
	xfs_ail_insert(
	struct xfs_ail *ailp,
	xfs_log_item_t *lip)
	/* ARGSUSED */
	{
	xfs_log_item_t *next_lip;

	/*
	* If the list is empty, just insert the item.
	*/
	if (list_empty(&ailp->xa_ail)) {
	list_add(&lip->li_ail, &ailp->xa_ail);
	return;
	}

	list_for_each_entry_reverse(next_lip, &ailp->xa_ail, li_ail) {
	if (XFS_LSN_CMP(next_lip->li_lsn, lip->li_lsn) <= 0)
	break;
	}

	ASSERT((&next_lip->li_ail == &ailp->xa_ail) \|\|
	(XFS_LSN_CMP(next_lip->li_lsn, lip->li_lsn) <= 0));

	list_add(&lip->li_ail, &next_lip->li_ail);

	xfs_ail_check(ailp, lip);
	return;
	}

	/*
	* Delete the given item from the AIL. Return a pointer to the item.
	*/
	/ARGSUSED/
	STATIC xfs_log_item_t *
	xfs_ail_delete(
	struct xfs_ail *ailp,
	xfs_log_item_t *lip)
	/* ARGSUSED */
	{
	xfs_ail_check(ailp, lip);

	list_del(&lip->li_ail);

	return lip;
	}

	/*
	* Return a pointer to the first item in the AIL.
	* If the AIL is empty, then return NULL.
	*/
	STATIC xfs_log_item_t *
	xfs_ail_min(
	struct xfs_ail *ailp)
	/* ARGSUSED */
	{
	if (list_empty(&ailp->xa_ail))
	return NULL;

	return list_first_entry(&ailp->xa_ail, xfs_log_item_t, li_ail);
	}

	/*
	* Return a pointer to the item which follows
	* the given item in the AIL. If the given item
	* is the last item in the list, then return NULL.
	*/
	STATIC xfs_log_item_t *
	xfs_ail_next(
	struct xfs_ail *ailp,
	xfs_log_item_t *lip)
	/* ARGSUSED */
	{
	if (lip->li_ail.next == &ailp->xa_ail)
	return NULL;

	return list_first_entry(&lip->li_ail, xfs_log_item_t, li_ail);
	}

	#ifdef DEBUG
	/*
	* Check that the list is sorted as it should be.
	*/
	STATIC void
	xfs_ail_check(
	struct xfs_ail *ailp,
	xfs_log_item_t *lip)
	{
	xfs_log_item_t *prev_lip;

	if (list_empty(&ailp->xa_ail))
	return;

	/*
	* Check the next and previous entries are valid.
	*/
	ASSERT((lip->li_flags & XFS_LI_IN_AIL) != 0);
	prev_lip = list_entry(lip->li_ail.prev, xfs_log_item_t, li_ail);
	if (&prev_lip->li_ail != &ailp->xa_ail)
	ASSERT(XFS_LSN_CMP(prev_lip->li_lsn, lip->li_lsn) <= 0);

	prev_lip = list_entry(lip->li_ail.next, xfs_log_item_t, li_ail);
	if (&prev_lip->li_ail != &ailp->xa_ail)
	ASSERT(XFS_LSN_CMP(prev_lip->li_lsn, lip->li_lsn) >= 0);


	#ifdef XFS_TRANS_DEBUG
	/*
	* Walk the list checking lsn ordering, and that every entry has the
	* XFS_LI_IN_AIL flag set. This is really expensive, so only do it
	* when specifically debugging the transaction subsystem.
	*/
	prev_lip = list_entry(&ailp->xa_ail, xfs_log_item_t, li_ail);
	list_for_each_entry(lip, &ailp->xa_ail, li_ail) {
	if (&prev_lip->li_ail != &ailp->xa_ail)
	ASSERT(XFS_LSN_CMP(prev_lip->li_lsn, lip->li_lsn) <= 0);
	ASSERT((lip->li_flags & XFS_LI_IN_AIL) != 0);
	prev_lip = lip;
	}
	#endif /* XFS_TRANS_DEBUG */
	}
	#endif /* DEBUG */