xfs: remove the m_active_trans counter

It's a global atomic counter, and we are hitting it at a rate of
half a million transactions a second, so it's bouncing the counter
cacheline all over the place on large machines. We don't actually
need it anymore - it used to be required because the VFS freeze code
could not track/prevent filesystem transactions that were running,
but that problem no longer exists.

Hence to remove the counter, we simply have to ensure that nothing
calls xfs_sync_sb() while we are trying to quiesce the filesytem.
That only happens if the log worker is still running when we call
xfs_quiesce_attr(). The log worker is cancelled at the end of
xfs_quiesce_attr() by calling xfs_log_quiesce(), so just call it
early here and then we can remove the counter altogether.

Concurrent create, 50 million inodes, identical 16p/16GB virtual
machines on different physical hosts. Machine A has twice the CPU
cores per socket of machine B:

		unpatched	patched
machine A:	3m16s		2m00s
machine B:	4m04s		4m05s

Create rates:
		unpatched	patched
machine A:	282k+/-31k	468k+/-21k
machine B:	231k+/-8k	233k+/-11k

Concurrent rm of same 50 million inodes:

		unpatched	patched
machine A:	6m42s		2m33s
machine B:	4m47s		4m47s

The transaction rate on the fast machine went from just under
300k/sec to 700k/sec, which indicates just how much of a bottleneck
this atomic counter was.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
This commit is contained in:
Dave Chinner 2020-05-20 13:17:11 -07:00 committed by Darrick J. Wong
parent b0dff466c0
commit b41b46c20c
3 changed files with 16 additions and 29 deletions

View File

@ -176,7 +176,6 @@ typedef struct xfs_mount {
uint64_t m_resblks; /* total reserved blocks */
uint64_t m_resblks_avail;/* available reserved blocks */
uint64_t m_resblks_save; /* reserved blks @ remount,ro */
atomic_t m_active_trans; /* number trans frozen */
struct delayed_work m_reclaim_work; /* background inode reclaim */
struct delayed_work m_eofblocks_work; /* background eof blocks
trimming */

View File

@ -874,8 +874,10 @@ xfs_restore_resvblks(struct xfs_mount *mp)
* there is no log replay required to write the inodes to disk - this is the
* primary difference between a sync and a quiesce.
*
* Note: xfs_log_quiesce() stops background log work - the callers must ensure
* it is started again when appropriate.
* We cancel log work early here to ensure all transactions the log worker may
* run have finished before we clean up and log the superblock and write an
* unmount record. The unfreeze process is responsible for restarting the log
* worker correctly.
*/
void
xfs_quiesce_attr(
@ -883,9 +885,7 @@ xfs_quiesce_attr(
{
int error = 0;
/* wait for all modifications to complete */
while (atomic_read(&mp->m_active_trans) > 0)
delay(100);
cancel_delayed_work_sync(&mp->m_log->l_work);
/* force the log to unpin objects from the now complete transactions */
xfs_log_force(mp, XFS_LOG_SYNC);
@ -899,12 +899,6 @@ xfs_quiesce_attr(
if (error)
xfs_warn(mp, "xfs_attr_quiesce: failed to log sb changes. "
"Frozen image may not be consistent.");
/*
* Just warn here till VFS can correctly support
* read-only remount without racing.
*/
WARN_ON(atomic_read(&mp->m_active_trans) != 0);
xfs_log_quiesce(mp);
}
@ -1793,7 +1787,6 @@ static int xfs_init_fs_context(
INIT_RADIX_TREE(&mp->m_perag_tree, GFP_ATOMIC);
spin_lock_init(&mp->m_perag_lock);
mutex_init(&mp->m_growlock);
atomic_set(&mp->m_active_trans, 0);
INIT_WORK(&mp->m_flush_inodes_work, xfs_flush_inodes_worker);
INIT_DELAYED_WORK(&mp->m_reclaim_work, xfs_reclaim_worker);
INIT_DELAYED_WORK(&mp->m_eofblocks_work, xfs_eofblocks_worker);

View File

@ -68,7 +68,6 @@ xfs_trans_free(
xfs_extent_busy_clear(tp->t_mountp, &tp->t_busy, false);
trace_xfs_trans_free(tp, _RET_IP_);
atomic_dec(&tp->t_mountp->m_active_trans);
if (!(tp->t_flags & XFS_TRANS_NO_WRITECOUNT))
sb_end_intwrite(tp->t_mountp->m_super);
xfs_trans_free_dqinfo(tp);
@ -125,8 +124,6 @@ xfs_trans_dup(
xfs_defer_move(ntp, tp);
xfs_trans_dup_dqinfo(tp, ntp);
atomic_inc(&tp->t_mountp->m_active_trans);
return ntp;
}
@ -275,7 +272,6 @@ xfs_trans_alloc(
*/
WARN_ON(resp->tr_logres > 0 &&
mp->m_super->s_writers.frozen == SB_FREEZE_COMPLETE);
atomic_inc(&mp->m_active_trans);
tp->t_magic = XFS_TRANS_HEADER_MAGIC;
tp->t_flags = flags;
@ -299,20 +295,19 @@ xfs_trans_alloc(
/*
* Create an empty transaction with no reservation. This is a defensive
* mechanism for routines that query metadata without actually modifying
* them -- if the metadata being queried is somehow cross-linked (think a
* btree block pointer that points higher in the tree), we risk deadlock.
* However, blocks grabbed as part of a transaction can be re-grabbed.
* The verifiers will notice the corrupt block and the operation will fail
* back to userspace without deadlocking.
* mechanism for routines that query metadata without actually modifying them --
* if the metadata being queried is somehow cross-linked (think a btree block
* pointer that points higher in the tree), we risk deadlock. However, blocks
* grabbed as part of a transaction can be re-grabbed. The verifiers will
* notice the corrupt block and the operation will fail back to userspace
* without deadlocking.
*
* Note the zero-length reservation; this transaction MUST be cancelled
* without any dirty data.
* Note the zero-length reservation; this transaction MUST be cancelled without
* any dirty data.
*
* Callers should obtain freeze protection to avoid two conflicts with fs
* freezing: (1) having active transactions trip the m_active_trans ASSERTs;
* and (2) grabbing buffers at the same time that freeze is trying to drain
* the buffer LRU list.
* Callers should obtain freeze protection to avoid a conflict with fs freezing
* where we can be grabbing buffers at the same time that freeze is trying to
* drain the buffer LRU list.
*/
int
xfs_trans_alloc_empty(