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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: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
This commit is contained in:
Dave Chinner 2010-12-03 22:11:29 +11:00 committed by Dave Chinner
parent 2ced19cbae
commit 84f3c683c4
3 changed files with 36 additions and 34 deletions
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55
fs/xfs/xfs_log.c
View File

@ -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) {
log->l_tail_lsn = tail_lsn;
} else {
tail_lsn = log->l_tail_lsn = log->l_last_sync_lsn;
}
if (!tail_lsn)
tail_lsn = atomic64_read(&log->l_last_sync_lsn);
log->l_tail_lsn = tail_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
@ -2194,7 +2191,7 @@ xlog_state_do_callback(
lowest_lsn = xlog_get_lowest_lsn(log);
if (lowest_lsn &&
XFS_LSN_CMP(lowest_lsn,
be64_to_cpu(iclog->ic_header.h_lsn)) < 0) {
be64_to_cpu(iclog->ic_header.h_lsn)) < 0) {
iclog = iclog->ic_next;
continue; /* Leave this iclog for
* another thread */
@ -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,
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);
ASSERT(XFS_LSN_CMP(atomic64_read(&log->l_last_sync_lsn),
be64_to_cpu(iclog->ic_header.h_lsn)) <= 0);
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

9
fs/xfs/xfs_log_priv.h
View File

@ -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];

6
fs/xfs/xfs_log_recover.c
View File

@ -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;
/*