fs/xfs/xfs_trans_ail.c - arm/linux - Git at Google

 /*
  * Copyright (c) 2000-2002 Silicon Graphics, Inc.  All Rights Reserved.
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms of version 2 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.
  *
  * Further, this software is distributed without any warranty that it is
  * free of the rightful claim of any third person regarding infringement
  * or the like.  Any license provided herein, whether implied or
  * otherwise, applies only to this software file.  Patent licenses, if
  * any, provided herein do not apply to combinations of this program with
  * other software, or any other product whatsoever.
  *
  * You should have received a copy of the GNU General Public License along
  * with this program; if not, write the Free Software Foundation, Inc., 59
  * Temple Place - Suite 330, Boston MA 02111-1307, USA.
  *
  * Contact information: Silicon Graphics, Inc., 1600 Amphitheatre Pkwy,
  * Mountain View, CA  94043, or:
  *
  * http://www.sgi.com
  *
  * For further information regarding this notice, see:
  *
  * http://oss.sgi.com/projects/GenInfo/SGIGPLNoticeExplan/
  */
 #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_dir.h"
 #include "xfs_dmapi.h"
 #include "xfs_mount.h"
 #include "xfs_trans_priv.h"
 #include "xfs_error.h"

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

 #ifdef DEBUG
 STATIC void xfs_ail_check(xfs_ail_entry_t *);
 #else
 #define	xfs_ail_check(a)
 #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_tail_ail(
 	xfs_mount_t	*mp)
 {
 	xfs_lsn_t	lsn;
 	xfs_log_item_t	*lip;
 	SPLDECL(s);

 	AIL_LOCK(mp,s);
 	lip = xfs_ail_min(&(mp->m_ail));
 	if (lip == NULL) {
 		lsn = (xfs_lsn_t)0;
 	} else {
 		lsn = lip->li_lsn;
 	}
 	AIL_UNLOCK(mp, s);

 	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 routine returns the lsn of the tail of the log.
  */
 xfs_lsn_t
 xfs_trans_push_ail(
 	xfs_mount_t		*mp,
 	xfs_lsn_t		threshold_lsn)
 {
 	xfs_lsn_t		lsn;
 	xfs_log_item_t		*lip;
 	int			gen;
 	int			restarts;
 	int			lock_result;
 	int			flush_log;
 	SPLDECL(s);

 #define	XFS_TRANS_PUSH_AIL_RESTARTS	10

 	AIL_LOCK(mp,s);
 	lip = xfs_trans_first_ail(mp, &gen);
 	if (lip == NULL || XFS_FORCED_SHUTDOWN(mp)) {
 		/*
 		 * Just return if the AIL is empty.
 		 */
 		AIL_UNLOCK(mp, s);
 		return (xfs_lsn_t)0;
 	}

 	XFS_STATS_INC(xs_push_ail);

 	/*
 	 * While the item we are looking at is below the given threshold
 	 * try to flush it out.  Make sure to limit the number of times
 	 * we allow xfs_trans_next_ail() to restart scanning from the
 	 * beginning of the list.  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 may give up before that if
 	 * we realize that we've been holding the AIL_LOCK for 'too long',
 	 * blocking interrupts. Currently, too long is < 500us roughly.
 	 */
 	flush_log = 0;
 	restarts = 0;
 	while (((restarts < XFS_TRANS_PUSH_AIL_RESTARTS) &&
 		(XFS_LSN_CMP(lip->li_lsn, threshold_lsn) < 0))) {
 		/*
 		 * 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.  Since we unlock the AIL while we flush the
 		 * item, the next routine may start over again at the
 		 * the beginning of the list if anything has changed.
 		 * That is what the generation count is for.
 		 *
 		 * 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);
 		switch (lock_result) {
 		      case XFS_ITEM_SUCCESS:
 			AIL_UNLOCK(mp, s);
 			XFS_STATS_INC(xs_push_ail_success);
 			IOP_PUSH(lip);
 			AIL_LOCK(mp,s);
 			break;

 		      case XFS_ITEM_PUSHBUF:
 			AIL_UNLOCK(mp, s);
 			XFS_STATS_INC(xs_push_ail_pushbuf);
 #ifdef XFSRACEDEBUG
 			delay_for_intr();
 			delay(300);
 #endif
 			ASSERT(lip->li_ops->iop_pushbuf);
 			ASSERT(lip);
 			IOP_PUSHBUF(lip);
 			AIL_LOCK(mp,s);
 			break;

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

 		      case XFS_ITEM_LOCKED:
 			XFS_STATS_INC(xs_push_ail_locked);
 			break;

 		      case XFS_ITEM_FLUSHING:
 			XFS_STATS_INC(xs_push_ail_flushing);
 			break;

 		      default:
 			ASSERT(0);
 			break;
 		}

 		lip = xfs_trans_next_ail(mp, lip, &gen, &restarts);
 		if (lip == NULL) {
 			break;
 		}
 		if (XFS_FORCED_SHUTDOWN(mp)) {
 			/*
 			 * Just return if we shut down during the last try.
 			 */
 			AIL_UNLOCK(mp, s);
 			return (xfs_lsn_t)0;
 		}

 	}

 	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.
 		 */
 		AIL_UNLOCK(mp, s);
 		XFS_STATS_INC(xs_push_ail_flush);
 		xfs_log_force(mp, (xfs_lsn_t)0, XFS_LOG_FORCE);
 		AIL_LOCK(mp, s);
 	}

 	lip = xfs_ail_min(&(mp->m_ail));
 	if (lip == NULL) {
 		lsn = (xfs_lsn_t)0;
 	} else {
 		lsn = lip->li_lsn;
 	}

 	AIL_UNLOCK(mp, s);
 	return lsn;
 }	/* xfs_trans_push_ail */


 /*
  * 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(
 	xfs_mount_t	*mp,
 	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(mp)) {
 		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(&mp->m_ail);

 	if (min_lip == lip)
 		xfs_log_move_tail(mp, 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.
  *
  * Increment 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, so the caller must pass in the
  * cookie returned by AIL_LOCK.
  */
 void
 xfs_trans_update_ail(
 	xfs_mount_t	*mp,
 	xfs_log_item_t	*lip,
 	xfs_lsn_t	lsn,
 	unsigned long	s)
 {
 	xfs_ail_entry_t		*ailp;
 	xfs_log_item_t		*dlip=NULL;
 	xfs_log_item_t		*mlip;	/* ptr to minimum lip */

 	ailp = &(mp->m_ail);
 	mlip = xfs_ail_min(ailp);

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

 	lip->li_lsn = lsn;

 	xfs_ail_insert(ailp, lip);
 	mp->m_ail_gen++;

 	if (mlip == dlip) {
 		mlip = xfs_ail_min(&(mp->m_ail));
 		AIL_UNLOCK(mp, s);
 		xfs_log_move_tail(mp, mlip->li_lsn);
 	} else {
 		AIL_UNLOCK(mp, s);
 	}


 }	/* 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, so the caller must pass in the
  * cookie returned by AIL_LOCK.
  */
 void
 xfs_trans_delete_ail(
 	xfs_mount_t	*mp,
 	xfs_log_item_t	*lip,
 	unsigned long	s)
 {
 	xfs_ail_entry_t		*ailp;
 	xfs_log_item_t		*dlip;
 	xfs_log_item_t		*mlip;

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


 		lip->li_flags &= ~XFS_LI_IN_AIL;
 		lip->li_lsn = 0;
 		mp->m_ail_gen++;

 		if (mlip == dlip) {
 			mlip = xfs_ail_min(&(mp->m_ail));
 			AIL_UNLOCK(mp, s);
 			xfs_log_move_tail(mp, (mlip ? mlip->li_lsn : 0));
 		} else {
 			AIL_UNLOCK(mp, s);
 		}
 	}
 	else {
 		/*
 		 * If the file system is not being shutdown, we are in
 		 * serious trouble if we get to this stage.
 		 */
 		if (XFS_FORCED_SHUTDOWN(mp))
 			AIL_UNLOCK(mp, s);
 		else {
 			xfs_cmn_err(XFS_PTAG_AILDELETE, CE_ALERT, mp,
 				"xfs_trans_delete_ail: attempting to delete a log item that is not in the AIL");
 			AIL_UNLOCK(mp, s);
 			xfs_force_shutdown(mp, XFS_CORRUPT_INCORE);
 		}
 	}
 }


 /*
  * Return the item in the AIL with the smallest lsn.
  * Return the current tree generation number for use
  * in calls to xfs_trans_next_ail().
  */
 xfs_log_item_t *
 xfs_trans_first_ail(
 	xfs_mount_t	*mp,
 	int		*gen)
 {
 	xfs_log_item_t	*lip;

 	lip = xfs_ail_min(&(mp->m_ail));
 	*gen = (int)mp->m_ail_gen;

 	return (lip);
 }

 /*
  * If the generation count of the tree has not changed since the
  * caller last took something from the AIL, then return the elmt
  * in the tree which follows the one given.  If the count has changed,
  * then return the minimum elmt of the AIL and bump the restarts counter
  * if one is given.
  */
 xfs_log_item_t *
 xfs_trans_next_ail(
 	xfs_mount_t	*mp,
 	xfs_log_item_t	*lip,
 	int		*gen,
 	int		*restarts)
 {
 	xfs_log_item_t	*nlip;

 	ASSERT(mp && lip && gen);
 	if (mp->m_ail_gen == *gen) {
 		nlip = xfs_ail_next(&(mp->m_ail), lip);
 	} else {
 		nlip = xfs_ail_min(&(mp->m_ail));
 		*gen = (int)mp->m_ail_gen;
 		if (restarts != NULL) {
 			XFS_STATS_INC(xs_push_ail_restarts);
 			(*restarts)++;
 		}
 	}

 	return (nlip);
 }


 /*
  * 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.
  */
 void
 xfs_trans_ail_init(
 	xfs_mount_t	*mp)
 {
 	mp->m_ail.ail_forw = (xfs_log_item_t*)&(mp->m_ail);
 	mp->m_ail.ail_back = (xfs_log_item_t*)&(mp->m_ail);
 }

 /*
  * 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(
 	xfs_ail_entry_t	*base,
 	xfs_log_item_t	*lip)
 /* ARGSUSED */
 {
 	xfs_log_item_t	*next_lip;

 	/*
 	 * If the list is empty, just insert the item.
 	 */
 	if (base->ail_back == (xfs_log_item_t*)base) {
 		base->ail_forw = lip;
 		base->ail_back = lip;
 		lip->li_ail.ail_forw = (xfs_log_item_t*)base;
 		lip->li_ail.ail_back = (xfs_log_item_t*)base;
 		return;
 	}

 	next_lip = base->ail_back;
 	while ((next_lip != (xfs_log_item_t*)base) &&
 	       (XFS_LSN_CMP(next_lip->li_lsn, lip->li_lsn) > 0)) {
 		next_lip = next_lip->li_ail.ail_back;
 	}
 	ASSERT((next_lip == (xfs_log_item_t*)base) ||
 	       (XFS_LSN_CMP(next_lip->li_lsn, lip->li_lsn) <= 0));
 	lip->li_ail.ail_forw = next_lip->li_ail.ail_forw;
 	lip->li_ail.ail_back = next_lip;
 	next_lip->li_ail.ail_forw = lip;
 	lip->li_ail.ail_forw->li_ail.ail_back = lip;

 	xfs_ail_check(base);
 	return;
 }

 /*
  * Delete the given item from the AIL.  Return a pointer to the item.
  */
 /*ARGSUSED*/
 STATIC xfs_log_item_t *
 xfs_ail_delete(
 	xfs_ail_entry_t	*base,
 	xfs_log_item_t	*lip)
 /* ARGSUSED */
 {
 	lip->li_ail.ail_forw->li_ail.ail_back = lip->li_ail.ail_back;
 	lip->li_ail.ail_back->li_ail.ail_forw = lip->li_ail.ail_forw;
 	lip->li_ail.ail_forw = NULL;
 	lip->li_ail.ail_back = NULL;

 	xfs_ail_check(base);
 	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(
 	xfs_ail_entry_t	*base)
 /* ARGSUSED */
 {
 	register xfs_log_item_t *forw = base->ail_forw;
 	if (forw == (xfs_log_item_t*)base) {
 		return NULL;
 	}
 	return forw;
 }

 /*
  * 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(
 	xfs_ail_entry_t	*base,
 	xfs_log_item_t	*lip)
 /* ARGSUSED */
 {
 	if (lip->li_ail.ail_forw == (xfs_log_item_t*)base) {
 		return NULL;
 	}
 	return lip->li_ail.ail_forw;

 }

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

 	lip = base->ail_forw;
 	if (lip == (xfs_log_item_t*)base) {
 		/*
 		 * Make sure the pointers are correct when the list
 		 * is empty.
 		 */
 		ASSERT(base->ail_back == (xfs_log_item_t*)base);
 		return;
 	}

 	/*
 	 * Walk the list checking forward and backward pointers,
 	 * lsn ordering, and that every entry has the XFS_LI_IN_AIL
 	 * flag set.
 	 */
 	prev_lip = (xfs_log_item_t*)base;
 	while (lip != (xfs_log_item_t*)base) {
 		if (prev_lip != (xfs_log_item_t*)base) {
 			ASSERT(prev_lip->li_ail.ail_forw == lip);
 			ASSERT(XFS_LSN_CMP(prev_lip->li_lsn, lip->li_lsn) <= 0);
 		}
 		ASSERT(lip->li_ail.ail_back == prev_lip);
 		ASSERT((lip->li_flags & XFS_LI_IN_AIL) != 0);
 		prev_lip = lip;
 		lip = lip->li_ail.ail_forw;
 	}
 	ASSERT(lip == (xfs_log_item_t*)base);
 	ASSERT(base->ail_back == prev_lip);
 }
 #endif /* DEBUG */
	/*
	* Copyright (c) 2000-2002 Silicon Graphics, Inc. All Rights Reserved.
	*
	* This program is free software; you can redistribute it and/or modify it
	* under the terms of version 2 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.
	*
	* Further, this software is distributed without any warranty that it is
	* free of the rightful claim of any third person regarding infringement
	* or the like. Any license provided herein, whether implied or
	* otherwise, applies only to this software file. Patent licenses, if
	* any, provided herein do not apply to combinations of this program with
	* other software, or any other product whatsoever.
	*
	* You should have received a copy of the GNU General Public License along
	* with this program; if not, write the Free Software Foundation, Inc., 59
	* Temple Place - Suite 330, Boston MA 02111-1307, USA.
	*
	* Contact information: Silicon Graphics, Inc., 1600 Amphitheatre Pkwy,
	* Mountain View, CA 94043, or:
	*
	* http://www.sgi.com
	*
	* For further information regarding this notice, see:
	*
	* http://oss.sgi.com/projects/GenInfo/SGIGPLNoticeExplan/
	*/
	#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_dir.h"
	#include "xfs_dmapi.h"
	#include "xfs_mount.h"
	#include "xfs_trans_priv.h"
	#include "xfs_error.h"

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

	#ifdef DEBUG
	STATIC void xfs_ail_check(xfs_ail_entry_t *);
	#else
	#define xfs_ail_check(a)
	#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_tail_ail(
	xfs_mount_t *mp)
	{
	xfs_lsn_t lsn;
	xfs_log_item_t *lip;
	SPLDECL(s);

	AIL_LOCK(mp,s);
	lip = xfs_ail_min(&(mp->m_ail));
	if (lip == NULL) {
	lsn = (xfs_lsn_t)0;
	} else {
	lsn = lip->li_lsn;
	}
	AIL_UNLOCK(mp, s);

	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 routine returns the lsn of the tail of the log.
	*/
	xfs_lsn_t
	xfs_trans_push_ail(
	xfs_mount_t *mp,
	xfs_lsn_t threshold_lsn)
	{
	xfs_lsn_t lsn;
	xfs_log_item_t *lip;
	int gen;
	int restarts;
	int lock_result;
	int flush_log;
	SPLDECL(s);

	#define XFS_TRANS_PUSH_AIL_RESTARTS 10

	AIL_LOCK(mp,s);
	lip = xfs_trans_first_ail(mp, &gen);
	if (lip == NULL \|\| XFS_FORCED_SHUTDOWN(mp)) {
	/*
	* Just return if the AIL is empty.
	*/
	AIL_UNLOCK(mp, s);
	return (xfs_lsn_t)0;
	}

	XFS_STATS_INC(xs_push_ail);

	/*
	* While the item we are looking at is below the given threshold
	* try to flush it out. Make sure to limit the number of times
	* we allow xfs_trans_next_ail() to restart scanning from the
	* beginning of the list. 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 may give up before that if
	* we realize that we've been holding the AIL_LOCK for 'too long',
	* blocking interrupts. Currently, too long is < 500us roughly.
	*/
	flush_log = 0;
	restarts = 0;
	while (((restarts < XFS_TRANS_PUSH_AIL_RESTARTS) &&
	(XFS_LSN_CMP(lip->li_lsn, threshold_lsn) < 0))) {
	/*
	* 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. Since we unlock the AIL while we flush the
	* item, the next routine may start over again at the
	* the beginning of the list if anything has changed.
	* That is what the generation count is for.
	*
	* 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);
	switch (lock_result) {
	case XFS_ITEM_SUCCESS:
	AIL_UNLOCK(mp, s);
	XFS_STATS_INC(xs_push_ail_success);
	IOP_PUSH(lip);
	AIL_LOCK(mp,s);
	break;

	case XFS_ITEM_PUSHBUF:
	AIL_UNLOCK(mp, s);
	XFS_STATS_INC(xs_push_ail_pushbuf);
	#ifdef XFSRACEDEBUG
	delay_for_intr();
	delay(300);
	#endif
	ASSERT(lip->li_ops->iop_pushbuf);
	ASSERT(lip);
	IOP_PUSHBUF(lip);
	AIL_LOCK(mp,s);
	break;

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

	case XFS_ITEM_LOCKED:
	XFS_STATS_INC(xs_push_ail_locked);
	break;

	case XFS_ITEM_FLUSHING:
	XFS_STATS_INC(xs_push_ail_flushing);
	break;

	default:
	ASSERT(0);
	break;
	}

	lip = xfs_trans_next_ail(mp, lip, &gen, &restarts);
	if (lip == NULL) {
	break;
	}
	if (XFS_FORCED_SHUTDOWN(mp)) {
	/*
	* Just return if we shut down during the last try.
	*/
	AIL_UNLOCK(mp, s);
	return (xfs_lsn_t)0;
	}

	}

	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.
	*/
	AIL_UNLOCK(mp, s);
	XFS_STATS_INC(xs_push_ail_flush);
	xfs_log_force(mp, (xfs_lsn_t)0, XFS_LOG_FORCE);
	AIL_LOCK(mp, s);
	}

	lip = xfs_ail_min(&(mp->m_ail));
	if (lip == NULL) {
	lsn = (xfs_lsn_t)0;
	} else {
	lsn = lip->li_lsn;
	}

	AIL_UNLOCK(mp, s);
	return lsn;
	} /* xfs_trans_push_ail */


	/*
	* 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(
	xfs_mount_t *mp,
	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(mp)) {
	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(&mp->m_ail);

	if (min_lip == lip)
	xfs_log_move_tail(mp, 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.
	*
	* Increment 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, so the caller must pass in the
	* cookie returned by AIL_LOCK.
	*/
	void
	xfs_trans_update_ail(
	xfs_mount_t *mp,
	xfs_log_item_t *lip,
	xfs_lsn_t lsn,
	unsigned long s)
	{
	xfs_ail_entry_t *ailp;
	xfs_log_item_t *dlip=NULL;
	xfs_log_item_t mlip; / ptr to minimum lip */

	ailp = &(mp->m_ail);
	mlip = xfs_ail_min(ailp);

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

	lip->li_lsn = lsn;

	xfs_ail_insert(ailp, lip);
	mp->m_ail_gen++;

	if (mlip == dlip) {
	mlip = xfs_ail_min(&(mp->m_ail));
	AIL_UNLOCK(mp, s);
	xfs_log_move_tail(mp, mlip->li_lsn);
	} else {
	AIL_UNLOCK(mp, s);
	}


	} /* 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, so the caller must pass in the
	* cookie returned by AIL_LOCK.
	*/
	void
	xfs_trans_delete_ail(
	xfs_mount_t *mp,
	xfs_log_item_t *lip,
	unsigned long s)
	{
	xfs_ail_entry_t *ailp;
	xfs_log_item_t *dlip;
	xfs_log_item_t *mlip;

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


	lip->li_flags &= ~XFS_LI_IN_AIL;
	lip->li_lsn = 0;
	mp->m_ail_gen++;

	if (mlip == dlip) {
	mlip = xfs_ail_min(&(mp->m_ail));
	AIL_UNLOCK(mp, s);
	xfs_log_move_tail(mp, (mlip ? mlip->li_lsn : 0));
	} else {
	AIL_UNLOCK(mp, s);
	}
	}
	else {
	/*
	* If the file system is not being shutdown, we are in
	* serious trouble if we get to this stage.
	*/
	if (XFS_FORCED_SHUTDOWN(mp))
	AIL_UNLOCK(mp, s);
	else {
	xfs_cmn_err(XFS_PTAG_AILDELETE, CE_ALERT, mp,
	"xfs_trans_delete_ail: attempting to delete a log item that is not in the AIL");
	AIL_UNLOCK(mp, s);
	xfs_force_shutdown(mp, XFS_CORRUPT_INCORE);
	}
	}
	}



	/*
	* Return the item in the AIL with the smallest lsn.
	* Return the current tree generation number for use
	* in calls to xfs_trans_next_ail().
	*/
	xfs_log_item_t *
	xfs_trans_first_ail(
	xfs_mount_t *mp,
	int *gen)
	{
	xfs_log_item_t *lip;

	lip = xfs_ail_min(&(mp->m_ail));
	*gen = (int)mp->m_ail_gen;

	return (lip);
	}

	/*
	* If the generation count of the tree has not changed since the
	* caller last took something from the AIL, then return the elmt
	* in the tree which follows the one given. If the count has changed,
	* then return the minimum elmt of the AIL and bump the restarts counter
	* if one is given.
	*/
	xfs_log_item_t *
	xfs_trans_next_ail(
	xfs_mount_t *mp,
	xfs_log_item_t *lip,
	int *gen,
	int *restarts)
	{
	xfs_log_item_t *nlip;

	ASSERT(mp && lip && gen);
	if (mp->m_ail_gen == *gen) {
	nlip = xfs_ail_next(&(mp->m_ail), lip);
	} else {
	nlip = xfs_ail_min(&(mp->m_ail));
	*gen = (int)mp->m_ail_gen;
	if (restarts != NULL) {
	XFS_STATS_INC(xs_push_ail_restarts);
	(*restarts)++;
	}
	}

	return (nlip);
	}


	/*
	* 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.
	*/
	void
	xfs_trans_ail_init(
	xfs_mount_t *mp)
	{
	mp->m_ail.ail_forw = (xfs_log_item_t*)&(mp->m_ail);
	mp->m_ail.ail_back = (xfs_log_item_t*)&(mp->m_ail);
	}

	/*
	* 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(
	xfs_ail_entry_t *base,
	xfs_log_item_t *lip)
	/* ARGSUSED */
	{
	xfs_log_item_t *next_lip;

	/*
	* If the list is empty, just insert the item.
	*/
	if (base->ail_back == (xfs_log_item_t*)base) {
	base->ail_forw = lip;
	base->ail_back = lip;
	lip->li_ail.ail_forw = (xfs_log_item_t*)base;
	lip->li_ail.ail_back = (xfs_log_item_t*)base;
	return;
	}

	next_lip = base->ail_back;
	while ((next_lip != (xfs_log_item_t*)base) &&
	(XFS_LSN_CMP(next_lip->li_lsn, lip->li_lsn) > 0)) {
	next_lip = next_lip->li_ail.ail_back;
	}
	ASSERT((next_lip == (xfs_log_item_t*)base) \|\|
	(XFS_LSN_CMP(next_lip->li_lsn, lip->li_lsn) <= 0));
	lip->li_ail.ail_forw = next_lip->li_ail.ail_forw;
	lip->li_ail.ail_back = next_lip;
	next_lip->li_ail.ail_forw = lip;
	lip->li_ail.ail_forw->li_ail.ail_back = lip;

	xfs_ail_check(base);
	return;
	}

	/*
	* Delete the given item from the AIL. Return a pointer to the item.
	*/
	/ARGSUSED/
	STATIC xfs_log_item_t *
	xfs_ail_delete(
	xfs_ail_entry_t *base,
	xfs_log_item_t *lip)
	/* ARGSUSED */
	{
	lip->li_ail.ail_forw->li_ail.ail_back = lip->li_ail.ail_back;
	lip->li_ail.ail_back->li_ail.ail_forw = lip->li_ail.ail_forw;
	lip->li_ail.ail_forw = NULL;
	lip->li_ail.ail_back = NULL;

	xfs_ail_check(base);
	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(
	xfs_ail_entry_t *base)
	/* ARGSUSED */
	{
	register xfs_log_item_t *forw = base->ail_forw;
	if (forw == (xfs_log_item_t*)base) {
	return NULL;
	}
	return forw;
	}

	/*
	* 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(
	xfs_ail_entry_t *base,
	xfs_log_item_t *lip)
	/* ARGSUSED */
	{
	if (lip->li_ail.ail_forw == (xfs_log_item_t*)base) {
	return NULL;
	}
	return lip->li_ail.ail_forw;

	}

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

	lip = base->ail_forw;
	if (lip == (xfs_log_item_t*)base) {
	/*
	* Make sure the pointers are correct when the list
	* is empty.
	*/
	ASSERT(base->ail_back == (xfs_log_item_t*)base);
	return;
	}

	/*
	* Walk the list checking forward and backward pointers,
	* lsn ordering, and that every entry has the XFS_LI_IN_AIL
	* flag set.
	*/
	prev_lip = (xfs_log_item_t*)base;
	while (lip != (xfs_log_item_t*)base) {
	if (prev_lip != (xfs_log_item_t*)base) {
	ASSERT(prev_lip->li_ail.ail_forw == lip);
	ASSERT(XFS_LSN_CMP(prev_lip->li_lsn, lip->li_lsn) <= 0);
	}
	ASSERT(lip->li_ail.ail_back == prev_lip);
	ASSERT((lip->li_flags & XFS_LI_IN_AIL) != 0);
	prev_lip = lip;
	lip = lip->li_ail.ail_forw;
	}
	ASSERT(lip == (xfs_log_item_t*)base);
	ASSERT(base->ail_back == prev_lip);
	}
	#endif /* DEBUG */