Commit 84f3c683 authored by Dave Chinner's avatar Dave Chinner Committed by Dave Chinner
Browse files

xfs: convert l_last_sync_lsn to an atomic variable 



log->l_last_sync_lsn is updated in only one critical spot - log
buffer Io completion - and is protected by the grant lock here. This
requires the grant lock to be taken for every log buffer IO
completion. Converting the l_last_sync_lsn variable to an atomic64_t
means that we do not need to take the grant lock in log buffer IO
completion to update it.

This also removes the need for explicitly holding a spinlock to read
the l_last_sync_lsn on 32 bit platforms.

Signed-off-by: default avatarDave Chinner <dchinner@redhat.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
parent 2ced19cb

fs/xfs/xfs_log.c

+25 −30
Original line number Diff line number Diff line
@@ -675,12 +675,8 @@ xfs_log_move_tail(xfs_mount_t *mp, 
	if (XLOG_FORCED_SHUTDOWN(log))

		return;



	if (tail_lsn == 0) {

		/* needed since sync_lsn is 64 bits */

		spin_lock(&log->l_icloglock);

		tail_lsn = log->l_last_sync_lsn;

		spin_unlock(&log->l_icloglock);

	}

	if (tail_lsn == 0)

		tail_lsn = atomic64_read(&log->l_last_sync_lsn);



	spin_lock(&log->l_grant_lock);
@@ -800,11 +796,9 @@ xlog_assign_tail_lsn(xfs_mount_t *mp) 


	tail_lsn = xfs_trans_ail_tail(mp->m_ail);

	spin_lock(&log->l_grant_lock);

	if (tail_lsn != 0) {

	if (!tail_lsn)

		tail_lsn = atomic64_read(&log->l_last_sync_lsn);

	log->l_tail_lsn = tail_lsn;

	} else {

		tail_lsn = log->l_tail_lsn = log->l_last_sync_lsn;

	}

	spin_unlock(&log->l_grant_lock);



	return tail_lsn;
@@ -1014,9 +1008,9 @@ xlog_alloc_log(xfs_mount_t *mp, 
	log->l_flags	   |= XLOG_ACTIVE_RECOVERY;



	log->l_prev_block  = -1;

	log->l_tail_lsn	   = xlog_assign_lsn(1, 0);

	/* log->l_tail_lsn = 0x100000000LL; cycle = 1; current block = 0 */

	log->l_last_sync_lsn = log->l_tail_lsn;

	log->l_tail_lsn	   = xlog_assign_lsn(1, 0);

	atomic64_set(&log->l_last_sync_lsn, xlog_assign_lsn(1, 0));

	log->l_curr_cycle  = 1;	    /* 0 is bad since this is initial value */

	xlog_assign_grant_head(&log->l_grant_reserve_head, 1, 0);

	xlog_assign_grant_head(&log->l_grant_write_head, 1, 0);
@@ -1194,6 +1188,7 @@ xlog_grant_push_ail( 
	int		need_bytes)

{

	xfs_lsn_t	threshold_lsn = 0;

	xfs_lsn_t	last_sync_lsn;

	xfs_lsn_t	tail_lsn;

	int		free_blocks;

	int		free_bytes;
@@ -1228,10 +1223,12 @@ xlog_grant_push_ail( 
					threshold_block);

	/*

	 * Don't pass in an lsn greater than the lsn of the last

	 * log record known to be on disk.

	 * log record known to be on disk. Use a snapshot of the last sync lsn

	 * so that it doesn't change between the compare and the set.

	 */

	if (XFS_LSN_CMP(threshold_lsn, log->l_last_sync_lsn) > 0)

		threshold_lsn = log->l_last_sync_lsn;

	last_sync_lsn = atomic64_read(&log->l_last_sync_lsn);

	if (XFS_LSN_CMP(threshold_lsn, last_sync_lsn) > 0)

		threshold_lsn = last_sync_lsn;



	/*

	 * Get the transaction layer to kick the dirty buffers out to
@@ -2202,23 +2199,21 @@ xlog_state_do_callback( 


				iclog->ic_state = XLOG_STATE_CALLBACK;



				spin_unlock(&log->l_icloglock);



				/* l_last_sync_lsn field protected by

				 * l_grant_lock. Don't worry about iclog's lsn.

				 * No one else can be here except us.

				/*

				 * update the last_sync_lsn before we drop the

				 * icloglock to ensure we are the only one that

				 * can update it.

				 */

				spin_lock(&log->l_grant_lock);

				ASSERT(XFS_LSN_CMP(log->l_last_sync_lsn,

				ASSERT(XFS_LSN_CMP(atomic64_read(&log->l_last_sync_lsn),

					be64_to_cpu(iclog->ic_header.h_lsn)) <= 0);

				log->l_last_sync_lsn =

					be64_to_cpu(iclog->ic_header.h_lsn);

				spin_unlock(&log->l_grant_lock);

				atomic64_set(&log->l_last_sync_lsn,

					be64_to_cpu(iclog->ic_header.h_lsn));



			} else {

				spin_unlock(&log->l_icloglock);

			} else

				ioerrors++;

			}



			spin_unlock(&log->l_icloglock);



			/*

			 * Keep processing entries in the callback list until

fs/xfs/xfs_log_priv.h

+8 −1
Original line number Diff line number Diff line
@@ -507,7 +507,6 @@ typedef struct log { 
	spinlock_t		l_icloglock;    /* grab to change iclog state */

	xfs_lsn_t		l_tail_lsn;     /* lsn of 1st LR with unflushed

						 * buffers */

	xfs_lsn_t		l_last_sync_lsn;/* lsn of last LR on disk */

	int			l_curr_cycle;   /* Cycle number of log writes */

	int			l_prev_cycle;   /* Cycle number before last

						 * block increment */
@@ -521,6 +520,14 @@ typedef struct log { 
	int64_t			l_grant_reserve_head;

	int64_t			l_grant_write_head;



	/*

	 * l_last_sync_lsn is an atomic so it can be set and read without

	 * needing to hold specific locks. To avoid operations contending with

	 * other hot objects, place it on a separate cacheline.

	 */

	/* lsn of last LR on disk */

	atomic64_t		l_last_sync_lsn ____cacheline_aligned_in_smp;



	/* The following field are used for debugging; need to hold icloglock */

#ifdef DEBUG

	char			*l_iclog_bak[XLOG_MAX_ICLOGS];

fs/xfs/xfs_log_recover.c

+3 −3
Original line number Diff line number Diff line
@@ -937,7 +937,7 @@ xlog_find_tail( 
	if (found == 2)

		log->l_curr_cycle++;

	log->l_tail_lsn = be64_to_cpu(rhead->h_tail_lsn);

	log->l_last_sync_lsn = be64_to_cpu(rhead->h_lsn);

	atomic64_set(&log->l_last_sync_lsn, be64_to_cpu(rhead->h_lsn));

	xlog_assign_grant_head(&log->l_grant_reserve_head, log->l_curr_cycle,

					BBTOB(log->l_curr_block));

	xlog_assign_grant_head(&log->l_grant_write_head, log->l_curr_cycle,
@@ -989,9 +989,9 @@ xlog_find_tail( 
			log->l_tail_lsn =

				xlog_assign_lsn(log->l_curr_cycle,

						after_umount_blk);

			log->l_last_sync_lsn =

			atomic64_set(&log->l_last_sync_lsn,

				xlog_assign_lsn(log->l_curr_cycle,

						after_umount_blk);

						after_umount_blk));

			*tail_blk = after_umount_blk;



			/*

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