Re: [PATCH 2/5] xfs: convert m_active_trans counter to per-cpu

[Brian Foster <bfoster@redhat.com>]

On Tue, May 12, 2020 at 07:28:08PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> 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. Convert it to a
> per-cpu counter.
> 
> And .... oh wow, that was unexpected!
> 
> 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:	3m45s		2m27s
> machine B:	4m13s		4m14s
> 
> Create rates:
> 		unpatched	patched
> machine A:	246k+/-15k	384k+/-10k
> machine B:	225k+/-13k	223k+/-11k
> 
> Concurrent rm of same 50 million inodes:
> 
> 		unpatched	patched
> machine A:	8m30s		3m09s
> machine B:	5m02s		4m51s
> 
> The transaction rate on the fast machine went from about 250k/sec to
> over 600k/sec, which indicates just how much of a bottleneck this
> atomic counter was.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---

Looks fairly straightforward. We're increasing the size of xfs_mount,
but it's already over a 4k page and there's only one per-mount:

Reviewed-by: Brian Foster <bfoster@redhat.com>

>  fs/xfs/xfs_mount.h |  2 +-
>  fs/xfs/xfs_super.c | 12 +++++++++---
>  fs/xfs/xfs_trans.c |  6 +++---
>  3 files changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
> index 712b3e2583316..af3d8b71e9591 100644
> --- a/fs/xfs/xfs_mount.h
> +++ b/fs/xfs/xfs_mount.h
> @@ -84,6 +84,7 @@ typedef struct xfs_mount {
>  	 * extents or anything related to the rt device.
>  	 */
>  	struct percpu_counter	m_delalloc_blks;
> +	struct percpu_counter	m_active_trans;	/* in progress xact counter */
>  
>  	struct xfs_buf		*m_sb_bp;	/* buffer for superblock */
>  	char			*m_rtname;	/* realtime device name */
> @@ -164,7 +165,6 @@ 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 xfs_mru_cache	*m_filestream;  /* per-mount filestream data */
>  	struct delayed_work	m_reclaim_work;	/* background inode reclaim */
>  	struct delayed_work	m_eofblocks_work; /* background eof blocks
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index e80bd2c4c279e..bc4853525ce18 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -883,7 +883,7 @@ xfs_quiesce_attr(
>  	int	error = 0;
>  
>  	/* wait for all modifications to complete */
> -	while (atomic_read(&mp->m_active_trans) > 0)
> +	while (percpu_counter_sum(&mp->m_active_trans) > 0)
>  		delay(100);
>  
>  	/* force the log to unpin objects from the now complete transactions */
> @@ -902,7 +902,7 @@ xfs_quiesce_attr(
>  	 * Just warn here till VFS can correctly support
>  	 * read-only remount without racing.
>  	 */
> -	WARN_ON(atomic_read(&mp->m_active_trans) != 0);
> +	WARN_ON(percpu_counter_sum(&mp->m_active_trans) != 0);
>  
>  	xfs_log_quiesce(mp);
>  }
> @@ -1027,8 +1027,14 @@ xfs_init_percpu_counters(
>  	if (error)
>  		goto free_fdblocks;
>  
> +	error = percpu_counter_init(&mp->m_active_trans, 0, GFP_KERNEL);
> +	if (error)
> +		goto free_delalloc_blocks;
> +
>  	return 0;
>  
> +free_delalloc_blocks:
> +	percpu_counter_destroy(&mp->m_delalloc_blks);
>  free_fdblocks:
>  	percpu_counter_destroy(&mp->m_fdblocks);
>  free_ifree:
> @@ -1057,6 +1063,7 @@ xfs_destroy_percpu_counters(
>  	ASSERT(XFS_FORCED_SHUTDOWN(mp) ||
>  	       percpu_counter_sum(&mp->m_delalloc_blks) == 0);
>  	percpu_counter_destroy(&mp->m_delalloc_blks);
> +	percpu_counter_destroy(&mp->m_active_trans);
>  }
>  
>  static void
> @@ -1792,7 +1799,6 @@ 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);
> diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
> index 28b983ff8b113..636df5017782e 100644
> --- a/fs/xfs/xfs_trans.c
> +++ b/fs/xfs/xfs_trans.c
> @@ -68,7 +68,7 @@ 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);
> +	percpu_counter_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);
> @@ -126,7 +126,7 @@ xfs_trans_dup(
>  
>  	xfs_trans_dup_dqinfo(tp, ntp);
>  
> -	atomic_inc(&tp->t_mountp->m_active_trans);
> +	percpu_counter_inc(&tp->t_mountp->m_active_trans);
>  	return ntp;
>  }
>  
> @@ -275,7 +275,7 @@ xfs_trans_alloc(
>  	 */
>  	WARN_ON(resp->tr_logres > 0 &&
>  		mp->m_super->s_writers.frozen == SB_FREEZE_COMPLETE);
> -	atomic_inc(&mp->m_active_trans);
> +	percpu_counter_inc(&mp->m_active_trans);
>  
>  	tp->t_magic = XFS_TRANS_HEADER_MAGIC;
>  	tp->t_flags = flags;
> -- 
> 2.26.1.301.g55bc3eb7cb9
>