Percona XtraDB 5.7 page cleaner

Hi,
i have log full of

2016-12-12T09:06:44.584605Z 0 [Note] InnoDB: page_cleaner: 1000ms intended loop took 7320ms. The settings might not be optimal. (flushed=15008, during the time.)
2016-12-12T09:06:55.980810Z 0 [Note] InnoDB: page_cleaner: 1000ms intended loop took 7395ms. The settings might not be optimal. (flushed=15008, during the time.)
2016-12-12T09:07:17.068971Z 0 [Note] InnoDB: page_cleaner: 1000ms intended loop took 6088ms. The settings might not be optimal. (flushed=15008, during the time.)
2016-12-12T09:07:27.348838Z 0 [Note] InnoDB: page_cleaner: 1000ms intended loop took 7279ms. The settings might not be optimal. (flushed=15008, during the time.)
2016-12-12T09:07:36.387946Z 0 [Note] InnoDB: page_cleaner: 1000ms intended loop took 6039ms. The settings might not be optimal. (flushed=15008, during the time.)
2016-12-12T09:07:55.278723Z 0 [Note] InnoDB: page_cleaner: 1000ms intended loop took 6278ms. The settings might not be optimal. (flushed=15008, during the time.)
2016-12-12T09:09:21.148997Z 0 [Note] InnoDB: page_cleaner: 1000ms intended loop took 6410ms. The settings might not be optimal. (flushed=15008, during the time.)
2016-12-12T09:09:34.891992Z 0 [Note] InnoDB: page_cleaner: 1000ms intended loop took 7743ms. The settings might not be optimal. (flushed=15008, during the time.)
2016-12-12T09:09:44.260456Z 0 [Note] InnoDB: page_cleaner: 1000ms intended loop took 6369ms. The settings might not be optimal. (flushed=15008, during the time.)

I tried to find out what parameter could have some influence on this, but without any success.

Please could you give me some suggestions?

Here is config of one of three nodes

# Template my.cnf for PXC
# Edit to your requirements.
[client]
socket=/var/lib/mysql/mysql.sock

[mysqld]
server-id=1
datadir=/var/lib/mysql
user=mysql
socket=/var/lib/mysql/mysql.sock
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid
log_syslog
log-bin
log_slave_updates
expire_logs_days=3
wait_timeout=2880000
interactive_timeout = 2880000

# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0

# Path to Galera library
wsrep_provider=/usr/lib64/galera3/libgalera_smm.so
wsrep_provider_options = "gcache.size=8G; gcs.fc_limit=1024"

# Cluster connection URL contains IPs of nodes
#If no IP is found, this implies that a new cluster needs to be created,
#in order to do that you need to bootstrap this node
wsrep_cluster_address=gcomm://10.5.3.26,10.5.3.27,10.5.3.28

# In order for Galera to work correctly binlog format should be ROW
binlog_format=ROW

# MyISAM storage engine has only experimental support
default_storage_engine=InnoDB

# Slave thread to use
wsrep_slave_threads= 4

wsrep_log_conflicts

# This changes how InnoDB autoincrement locks are managed and is a requirement for Galera
innodb_autoinc_lock_mode=2

# Node IP address
wsrep_node_address=10.5.3.28
# Cluster name
wsrep_cluster_name=my-pxc-cluster


#If wsrep_node_name is not specified, then system hostname will be used
wsrep_node_name=percona3

#pxc_strict_mode allowed values: DISABLED,PERMISSIVE,ENFORCING,MASTER
pxc_strict_mode=ENFORCING

# SST method
wsrep_sst_method=xtrabackup-v2

#Authentication for SST method
wsrep_sst_auth="sstuser:s3cretPass"

# SAFETY #
max-allowed-packet= 128M
max-connect-errors= 1000000
skip-name-resolve

# local part
sql-mode=NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
#federated
log_bin_trust_function_creators = 1

tmp-table-size=32M
max-heap-table-size=32M
query-cache-type=0
query-cache-size=0
max-connections=2500
thread-cache-size=50
table-definition-cache=4096
table_open_cache_instances=64
table_open_cache=5000

# INNODB #
innodb-flush-method=O_DIRECT
innodb_flush_neighbors=0
innodb_read_io_threads=16
innodb_write_io_threads=16
innodb_lru_scan_depth=512
innodb_io_capacity=15000
innodb_io_capacity_max=25000
innodb-log-files-in-group = 2
innodb-log-file-size = 10G
innodb-flush-log-at-trx-commit=1
innodb-file-per-table=1
innodb-buffer-pool-size=54G
innodb_buffer_pool_instances=32
innodb_change_buffering=none
innodb_adaptive_hash_index=OFF
innodb_log_buffer_size=256M
innodb_thread_concurrency= 0
thread_handling=pool-of-threads
innodb_page_cleaners=32
thread_pool_size=24
thread_cache_size = 20

innodb_use_native_aio = 0

# LOGGING #
log-error = /var/log/mysql-error.log
log-queries-not-using-indexes = 1
slow-query-log = 1
slow-query-log-file = /var/lib/mysql/mysql-slow.log

tmp_table_size = 200M
max_heap_table_size = 300M
key_buffer_size = 300M
tmpdir = /var/tmp

Thanks

Petr