From: Dave Chinner <dchinner@xxxxxxxxxx>
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@xxxxxxxxxx>
---
fs/xfs/xfs_log.c | 57 ++++++++++++++++++++-------------------------
fs/xfs/xfs_log_priv.h | 9 ++++++-
fs/xfs/xfs_log_recover.c | 6 ++--
3 files changed, 36 insertions(+), 36 deletions(-)
diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index a35ef8f..90a605cc 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -360,7 +360,7 @@ xfs_log_reserve(
spin_lock(&log->l_grant_lock);
xlog_grant_push_ail(log, log->l_tail_lsn,
- log->l_last_sync_lsn,
+ atomic64_read(&log->l_last_sync_lsn),
internal_ticket->t_unit_res);
spin_unlock(&log->l_grant_lock);
retval = xlog_regrant_write_log_space(log, internal_ticket);
@@ -378,7 +378,7 @@ xfs_log_reserve(
spin_lock(&log->l_grant_lock);
xlog_grant_push_ail(log, log->l_tail_lsn,
- log->l_last_sync_lsn,
+ atomic64_read(&log->l_last_sync_lsn),
(internal_ticket->t_unit_res *
internal_ticket->t_cnt));
spin_unlock(&log->l_grant_lock);
@@ -718,12 +718,8 @@ 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);
@@ -845,11 +841,9 @@ 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;
@@ -1057,10 +1051,9 @@ 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_curr_cycle = 1; /* 0 is bad since this is initial value */
+ log->l_tail_lsn = xlog_assign_lsn(1, 0);
+ atomic64_set(&log->l_last_sync_lsn, log->l_tail_lsn);
log->l_grant_reserve_lsn = xlog_assign_lsn(1, 0);
log->l_grant_write_lsn = xlog_assign_lsn(1, 0);
INIT_LIST_HEAD(&log->l_reserveq);
@@ -2241,7 +2234,7 @@ 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 */
@@ -2249,23 +2242,21 @@ 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
@@ -2576,7 +2567,8 @@ redo:
list_add_tail(&tic->t_queue, &log->l_reserveq);
xlog_grant_push_ail(log, log->l_tail_lsn,
- log->l_last_sync_lsn, need_bytes);
+ atomic64_read(&log->l_last_sync_lsn),
+ need_bytes);
XFS_STATS_INC(xs_sleep_logspace);
trace_xfs_log_grant_sleep(log, tic);
@@ -2683,7 +2675,8 @@ redo:
}
xlog_grant_push_ail(log, log->l_tail_lsn,
- log->l_last_sync_lsn, need_bytes);
+ atomic64_read(&log->l_last_sync_lsn),
+ need_bytes);
XFS_STATS_INC(xs_sleep_logspace);
trace_xfs_log_regrant_write_sleep(log, tic);
diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
index 6fcee10..97db8a8 100644
--- a/fs/xfs/xfs_log_priv.h
+++ b/fs/xfs/xfs_log_priv.h
@@ -508,7 +508,6 @@ 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 */
@@ -522,6 +521,14 @@ typedef struct log {
xfs_lsn_t l_grant_reserve_lsn;
xfs_lsn_t l_grant_write_lsn;
+ /*
+ * 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];
diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index d8c62f0..2ce7b48 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -926,7 +926,7 @@ 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));
log->l_grant_reserve_lsn = xlog_assign_lsn(log->l_curr_cycle,
BBTOB(log->l_curr_block));
log->l_grant_write_lsn = xlog_assign_lsn(log->l_curr_cycle,
@@ -978,9 +978,9 @@ 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;
/*
--
1.7.2.3
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