MDEV-11025: Make number of page cleaner threads variable dynamic

New test cases
        innodb-page-cleaners

Modified test cases
        innodb_page_cleaners_basic

New function buf_flush_set_page_cleaner_thread_cnt
    Increase or decrease the amount of page cleaner worker threads.
    In case of increase this function creates based on current
    abount and requested amount how many new threads should be
    created. In case of decrease this function sets up the
    requested amount of threads and uses is_requested event
    to signal workers. Then we wait until all new treads
    are started, old threads that should exit signal
    is_finished or shutdown has marked that page cleaner
    should finish.

buf_flush_page_cleaner_worker
        Store current thread id and thread_no and then signal
        event is_finished. If number of used page cleaner threads
        decrease we shut down those threads that have thread_no
        greater or equal than number of page configured page
        cleaners - 1 (note that there will be always page cleaner
        coordinator). Before exiting we signal is_finished.

New function innodb_page_cleaners_threads_update
        Update function for innodb-page-cleaners system variable.

innobase_start_or_create_for_mysql
        If more than one page cleaner threads is configured
        we use new function buf_flush_set_page_cleaner_thread_cnt
        to set up the requested threads (-1 coordinator).

mysql-test/suite/innodb/r/innodb-page-cleaners.result

+SET @saved_page_cleaners = @@GLOBAL.innodb_page_cleaners;
+create table t1 (a int not null primary key auto_increment,
+b bigint,
+c varchar(200),
+d int,
+key b (b),
+key d (d)) engine=INNODB;
+set GLOBAL innodb_page_cleaners = 4;
+connect  con1,localhost,root,,;
+connection con1;
+update t1 set b = b + 5, d = d + 1 where a between 1 and 2000;
+connect  con2,localhost,root,,;
+connection con2;
+update t1 set b = b + 5, d = d + 1 where a between 3000 and 5000;
+connect  con3,localhost,root,,;
+connection con3;
+update t1 set b = b + 5, d = d + 1 where a between 8000 and 12000;
+connection default;
+set GLOBAL innodb_page_cleaners = 2;
+set GLOBAL innodb_page_cleaners = 4;
+set GLOBAL innodb_page_cleaners = 6;
+connection con1;
+connection con2;
+connection con3;
+connection default;
+set GLOBAL innodb_page_cleaners = 4;
+connection con1;
+update t1 set b = b + 5, d = d + 1 where a between 1 and 2000;
+connection con2;
+update t1 set b = b + 5, d = d + 1 where a between 3000 and 5000;
+connection con3;
+update t1 set b = b + 5, d = d + 1 where a between 8000 and 12000;
+connection default;
+set GLOBAL innodb_page_cleaners = 3;
+set GLOBAL innodb_page_cleaners = 2;
+set GLOBAL innodb_page_cleaners = 1;
+connection con1;
+connection con2;
+connection con3;
+connection default;
+disconnect con1;
+disconnect con2;
+disconnect con3;
+DROP TABLE t1;
+SET GLOBAL innodb_page_cleaners=@saved_page_cleaners;

mysql-test/suite/innodb/t/innodb-page-cleaners.test

+--source include/have_innodb.inc
+
+SET @saved_page_cleaners = @@GLOBAL.innodb_page_cleaners;
+
+create table t1 (a int not null primary key auto_increment,
+b bigint,
+c varchar(200),
+d int,
+key b (b),
+key d (d)) engine=INNODB;
+
+let $rows = 15000;
+--disable_query_log
+begin;
+while ($rows)
+{
+    eval insert into t1 values(NULL, $rows, 'testing...', $rows+1000);
+    dec $rows;
+}
+commit;
+--enable_query_log
+
+#
+# We want 4 connections: (1) - (3) to create dirty pages
+# and default to modify the number of page cleaner threads
+#
+
+set GLOBAL innodb_page_cleaners = 4;
+
+connect (con1,localhost,root,,);
+connection con1;
+send update t1 set b = b + 5, d = d + 1 where a between 1 and 2000;
+
+connect (con2,localhost,root,,);
+connection con2;
+send update t1 set b = b + 5, d = d + 1 where a between 3000 and 5000;
+
+
+connect (con3,localhost,root,,);
+connection con3;
+send update t1 set b = b + 5, d = d + 1 where a between 8000 and 12000;
+
+#
+# Page cleaners are increased
+#
+
+connection default;
+set GLOBAL innodb_page_cleaners = 2;
+set GLOBAL innodb_page_cleaners = 4;
+set GLOBAL innodb_page_cleaners = 6;
+
+connection con1;
+reap;
+
+connection con2;
+reap;
+
+connection con3;
+reap;
+
+connection default;
+set GLOBAL innodb_page_cleaners = 4;
+
+#
+# Page cleaners are decreased
+#
+
+connection con1;
+send update t1 set b = b + 5, d = d + 1 where a between 1 and 2000;
+
+connection con2;
+send update t1 set b = b + 5, d = d + 1 where a between 3000 and 5000;
+
+connection con3;
+send update t1 set b = b + 5, d = d + 1 where a between 8000 and 12000;
+
+connection default;
+set GLOBAL innodb_page_cleaners = 3;
+set GLOBAL innodb_page_cleaners = 2;
+set GLOBAL innodb_page_cleaners = 1;
+
+connection con1;
+reap;
+
+connection con2;
+reap;
+
+connection con3;
+reap;
+
+connection default;
+disconnect con1;
+disconnect con2;
+disconnect con3;
+
+DROP TABLE t1;
+
+SET GLOBAL innodb_page_cleaners=@saved_page_cleaners;

mysql-test/suite/sys_vars/r/innodb_page_cleaners_basic.result

@@ -2,13 +2,42 @@ SELECT COUNT(@@GLOBAL.innodb_page_cleaners);
 COUNT(@@GLOBAL.innodb_page_cleaners)
 1
 1 Expected
-SELECT COUNT(@@innodb_page_cleaners);
-COUNT(@@innodb_page_cleaners)
+SELECT @@innodb_page_cleaners;
+@@innodb_page_cleaners
 1
 1 Expected
+SET @@GLOBAL.innodb_page_cleaners=2;
+Expected to pass
+SELECT @@innodb_page_cleaners;
+@@innodb_page_cleaners
+2
+2 Expected
 SET @@GLOBAL.innodb_page_cleaners=1;
-ERROR HY000: Variable 'innodb_page_cleaners' is a read only variable
-Expected error 'Read-only variable'
+Expected to pass
+SELECT @@innodb_page_cleaners;
+@@innodb_page_cleaners
+1
+1 Expected
+SET @@GLOBAL.innodb_page_cleaners=6;
+Expected to pass
+SELECT @@innodb_page_cleaners;
+@@innodb_page_cleaners
+6
+6 Expected
+SET @@GLOBAL.innodb_page_cleaners=4;
+Expected to pass
+SELECT @@innodb_page_cleaners;
+@@innodb_page_cleaners
+4
+4 Expected
+SET @@GLOBAL.innodb_page_cleaners=0;
+Warnings:
+Warning	1292	Truncated incorrect innodb_page_cleaners value: '0'
+Warning expected
+SELECT @@innodb_page_cleaners;
+@@innodb_page_cleaners
+1
+1 Expected
 SELECT innodb_page_cleaners = @@SESSION.innodb_page_cleaners;
 ERROR 42S22: Unknown column 'innodb_page_cleaners' in 'field list'
 Expected error 'Read-only variable'

mysql-test/suite/sys_vars/r/sysvars_debug,32bit.rdiff

---- suite/sys_vars/r/sysvars_debug.result	2014-10-10 13:33:55.000000000 +0300
-+++ suite/sys_vars/r/sysvars_debug,32bit.reject	2014-10-10 19:36:44.000000000 +0300
+--- r\sysvars_debug.result	2017-08-08 10:52:39.036804900 +0300
++++ r\sysvars_debug,32bit.reject	2017-09-10 08:06:38.447122100 +0300
 @@ -21,7 +21,7 @@
  GLOBAL_VALUE_ORIGIN	CONFIG
  DEFAULT_VALUE	0
@@ -9,3 +9,24 @@
  VARIABLE_COMMENT	Extra sleep (in microseconds) to add to binlog fsync(), for debugging
  NUMERIC_MIN_VALUE	0
  NUMERIC_MAX_VALUE	4294967295
+@@ -43,20 +43,6 @@
+ ENUM_VALUE_LIST	NULL
+ READ_ONLY	NO
+ COMMAND_LINE_ARGUMENT	OPTIONAL
+-VARIABLE_NAME	DEBUG_MUTEX_DEADLOCK_DETECTOR
+-SESSION_VALUE	NULL
+-GLOBAL_VALUE	ON
+-GLOBAL_VALUE_ORIGIN	COMPILE-TIME
+-DEFAULT_VALUE	ON
+-VARIABLE_SCOPE	GLOBAL
+-VARIABLE_TYPE	BOOLEAN
+-VARIABLE_COMMENT	Enable checking of wrong mutex usage
+-NUMERIC_MIN_VALUE	NULL
+-NUMERIC_MAX_VALUE	NULL
+-NUMERIC_BLOCK_SIZE	NULL
+-ENUM_VALUE_LIST	OFF,ON
+-READ_ONLY	YES
+-COMMAND_LINE_ARGUMENT	OPTIONAL
+ VARIABLE_NAME	DEBUG_NO_THREAD_ALARM
+ SESSION_VALUE	NULL
+ GLOBAL_VALUE	OFF

mysql-test/suite/sys_vars/r/sysvars_innodb,32bit.rdiff

---- suite/sys_vars/r/sysvars_innodb.result	2017-05-10 10:25:27.196836832 +0200
-+++ suite/sys_vars/r/sysvars_innodb.reject	2017-05-10 17:54:00.922046824 +0200
+--- suite/sys_vars/r/sysvars_innodb.result	2017-09-14 10:37:46.000000000 +0000
++++ suite/sys_vars/r/sysvars_innodb,32bit.reject	2017-09-26 13:13:23.685012523 +0000
 @@ -54,7 +54,7 @@
  GLOBAL_VALUE_ORIGIN	COMPILE-TIME
  DEFAULT_VALUE	8
@@ -364,7 +364,7 @@
  VARIABLE_COMMENT	Maximum delay of user threads in micro-seconds
  NUMERIC_MIN_VALUE	0
  NUMERIC_MAX_VALUE	10000000
-@@ -1692,10 +1692,10 @@
+@@ -1678,10 +1678,10 @@
  GLOBAL_VALUE_ORIGIN	COMPILE-TIME
  DEFAULT_VALUE	0
  VARIABLE_SCOPE	GLOBAL
@@ -377,7 +377,7 @@
  NUMERIC_BLOCK_SIZE	0
  ENUM_VALUE_LIST	NULL
  READ_ONLY	YES
-@@ -1720,7 +1720,7 @@
+@@ -1706,7 +1706,7 @@
  GLOBAL_VALUE_ORIGIN	COMPILE-TIME
  DEFAULT_VALUE	4
  VARIABLE_SCOPE	GLOBAL
@@ -386,7 +386,7 @@
  VARIABLE_COMMENT	Page cleaner threads can be from 1 to 64. Default is 4.
  NUMERIC_MIN_VALUE	1
  NUMERIC_MAX_VALUE	64
-@@ -1748,7 +1748,7 @@
+@@ -1734,7 +1734,7 @@
  GLOBAL_VALUE_ORIGIN	COMPILE-TIME
  DEFAULT_VALUE	16
  VARIABLE_SCOPE	GLOBAL
@@ -395,7 +395,7 @@
  VARIABLE_COMMENT	Number of rw_locks protecting buffer pool page_hash. Rounded up to the next power of 2
  NUMERIC_MIN_VALUE	1
  NUMERIC_MAX_VALUE	1024
-@@ -1762,7 +1762,7 @@
+@@ -1748,7 +1748,7 @@
  GLOBAL_VALUE_ORIGIN	COMPILE-TIME
  DEFAULT_VALUE	16384
  VARIABLE_SCOPE	GLOBAL
@@ -404,7 +404,7 @@
  VARIABLE_COMMENT	Page size to use for all InnoDB tablespaces.
  NUMERIC_MIN_VALUE	4096
  NUMERIC_MAX_VALUE	65536
-@@ -1804,7 +1804,7 @@
+@@ -1790,7 +1790,7 @@
  GLOBAL_VALUE_ORIGIN	COMPILE-TIME
  DEFAULT_VALUE	300
  VARIABLE_SCOPE	GLOBAL
@@ -413,7 +413,7 @@
  VARIABLE_COMMENT	Number of UNDO log pages to purge in one batch from the history list.
  NUMERIC_MIN_VALUE	1
  NUMERIC_MAX_VALUE	5000
-@@ -1818,7 +1818,7 @@
+@@ -1804,7 +1804,7 @@
  GLOBAL_VALUE_ORIGIN	COMPILE-TIME
  DEFAULT_VALUE	128
  VARIABLE_SCOPE	GLOBAL
@@ -422,7 +422,7 @@
  VARIABLE_COMMENT	Dictates rate at which UNDO records are purged. Value N means purge rollback segment(s) on every Nth iteration of purge invocation
  NUMERIC_MIN_VALUE	1
  NUMERIC_MAX_VALUE	128
-@@ -1860,7 +1860,7 @@
+@@ -1846,7 +1846,7 @@
  GLOBAL_VALUE_ORIGIN	COMPILE-TIME
  DEFAULT_VALUE	4
  VARIABLE_SCOPE	GLOBAL
@@ -431,7 +431,7 @@
  VARIABLE_COMMENT	Purge threads can be from 1 to 32. Default is 4.
  NUMERIC_MIN_VALUE	1
  NUMERIC_MAX_VALUE	32
-@@ -1888,7 +1888,7 @@
+@@ -1874,7 +1874,7 @@
  GLOBAL_VALUE_ORIGIN	COMPILE-TIME
  DEFAULT_VALUE	56
  VARIABLE_SCOPE	GLOBAL
@@ -440,7 +440,7 @@
  VARIABLE_COMMENT	Number of pages that must be accessed sequentially for InnoDB to trigger a readahead.
  NUMERIC_MIN_VALUE	0
  NUMERIC_MAX_VALUE	64
-@@ -1902,7 +1902,7 @@
+@@ -1888,7 +1888,7 @@
  GLOBAL_VALUE_ORIGIN	CONFIG
  DEFAULT_VALUE	4
  VARIABLE_SCOPE	GLOBAL
@@ -449,7 +449,7 @@
  VARIABLE_COMMENT	Number of background read I/O threads in InnoDB.
  NUMERIC_MIN_VALUE	1
  NUMERIC_MAX_VALUE	64
-@@ -1930,10 +1930,10 @@
+@@ -1916,10 +1916,10 @@
  GLOBAL_VALUE_ORIGIN	COMPILE-TIME
  DEFAULT_VALUE	0
  VARIABLE_SCOPE	GLOBAL
@@ -462,7 +462,7 @@
  NUMERIC_BLOCK_SIZE	0
  ENUM_VALUE_LIST	NULL
  READ_ONLY	NO
-@@ -1958,7 +1958,7 @@
+@@ -1944,7 +1944,7 @@
  GLOBAL_VALUE_ORIGIN	COMPILE-TIME
  DEFAULT_VALUE	128
  VARIABLE_SCOPE	GLOBAL
@@ -471,7 +471,7 @@
  VARIABLE_COMMENT	Number of undo logs to use (deprecated).
  NUMERIC_MIN_VALUE	1
  NUMERIC_MAX_VALUE	128
-@@ -1972,7 +1972,7 @@
+@@ -1958,7 +1958,7 @@
  GLOBAL_VALUE_ORIGIN	COMPILE-TIME
  DEFAULT_VALUE	0
  VARIABLE_SCOPE	GLOBAL
@@ -480,7 +480,7 @@
  VARIABLE_COMMENT	An InnoDB page number.
  NUMERIC_MIN_VALUE	0
  NUMERIC_MAX_VALUE	4294967295
-@@ -2028,7 +2028,7 @@
+@@ -2014,7 +2014,7 @@
  GLOBAL_VALUE_ORIGIN	COMPILE-TIME
  DEFAULT_VALUE	1048576
  VARIABLE_SCOPE	GLOBAL
@@ -489,7 +489,7 @@
  VARIABLE_COMMENT	Memory buffer size for index creation
  NUMERIC_MIN_VALUE	65536
  NUMERIC_MAX_VALUE	67108864
-@@ -2238,7 +2238,7 @@
+@@ -2224,7 +2224,7 @@
  GLOBAL_VALUE_ORIGIN	COMPILE-TIME
  DEFAULT_VALUE	1
  VARIABLE_SCOPE	GLOBAL
@@ -498,7 +498,7 @@
  VARIABLE_COMMENT	Size of the mutex/lock wait array.
  NUMERIC_MIN_VALUE	1
  NUMERIC_MAX_VALUE	1024
-@@ -2266,10 +2266,10 @@
+@@ -2252,10 +2252,10 @@
  GLOBAL_VALUE_ORIGIN	COMPILE-TIME
  DEFAULT_VALUE	30
  VARIABLE_SCOPE	GLOBAL
@@ -511,7 +511,7 @@
  NUMERIC_BLOCK_SIZE	0
  ENUM_VALUE_LIST	NULL
  READ_ONLY	NO
-@@ -2308,7 +2308,7 @@
+@@ -2294,7 +2294,7 @@
  GLOBAL_VALUE_ORIGIN	COMPILE-TIME
  DEFAULT_VALUE	0
  VARIABLE_SCOPE	GLOBAL
@@ -520,7 +520,7 @@
  VARIABLE_COMMENT	Helps in performance tuning in heavily concurrent environments. Sets the maximum number of threads allowed inside InnoDB. Value 0 will disable the thread throttling.
  NUMERIC_MIN_VALUE	0
  NUMERIC_MAX_VALUE	1000
-@@ -2322,7 +2322,7 @@
+@@ -2308,7 +2308,7 @@
  GLOBAL_VALUE_ORIGIN	COMPILE-TIME
  DEFAULT_VALUE	10000
  VARIABLE_SCOPE	GLOBAL
@@ -529,7 +529,7 @@
  VARIABLE_COMMENT	Time of innodb thread sleeping before joining InnoDB queue (usec). Value 0 disable a sleep
  NUMERIC_MIN_VALUE	0
  NUMERIC_MAX_VALUE	1000000
-@@ -2392,7 +2392,7 @@
+@@ -2378,7 +2378,7 @@
  GLOBAL_VALUE_ORIGIN	COMPILE-TIME
  DEFAULT_VALUE	128
  VARIABLE_SCOPE	GLOBAL
@@ -538,7 +538,7 @@
  VARIABLE_COMMENT	Number of undo logs to use.
  NUMERIC_MIN_VALUE	1
  NUMERIC_MAX_VALUE	128
-@@ -2420,7 +2420,7 @@
+@@ -2406,7 +2406,7 @@
  GLOBAL_VALUE_ORIGIN	COMPILE-TIME
  DEFAULT_VALUE	0
  VARIABLE_SCOPE	GLOBAL
@@ -547,7 +547,7 @@
  VARIABLE_COMMENT	Number of undo tablespaces to use.
  NUMERIC_MIN_VALUE	0
  NUMERIC_MAX_VALUE	127
-@@ -2476,7 +2476,7 @@
+@@ -2448,7 +2448,7 @@
  GLOBAL_VALUE_ORIGIN	CONFIG
  DEFAULT_VALUE	4
  VARIABLE_SCOPE	GLOBAL

mysql-test/suite/sys_vars/r/sysvars_innodb.result

@@ -1712,8 +1712,8 @@ NUMERIC_MIN_VALUE	1
 NUMERIC_MAX_VALUE	64
 NUMERIC_BLOCK_SIZE	0
 ENUM_VALUE_LIST	NULL
-READ_ONLY	YES
-COMMAND_LINE_ARGUMENT	OPTIONAL
+READ_ONLY	NO
+COMMAND_LINE_ARGUMENT	REQUIRED
 VARIABLE_NAME	INNODB_PAGE_CLEANER_DISABLED_DEBUG
 SESSION_VALUE	NULL
 GLOBAL_VALUE	OFF

mysql-test/suite/sys_vars/r/sysvars_server_notembedded,32bit.rdiff

---- a/mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result
-+++ b/mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result
+--- suite/sys_vars/r/sysvars_server_notembedded.result	2017-09-14 10:37:46.000000000 +0000
++++ suite/sys_vars/r/sysvars_server_notembedded,32bit.reject	2017-09-26 13:04:02.733012523 +0000
 @@ -57,7 +57,7 @@
  GLOBAL_VALUE_ORIGIN	CONFIG
  DEFAULT_VALUE	1

mysql-test/suite/sys_vars/t/innodb_page_cleaners_basic.test

 # Variable name: innodb_page_cleaners
 # Scope: Global
-# Access type: Static
+# Access type: Dynamic
 # Data type: numeric
 
 --source include/have_innodb.inc
@@ -8,12 +8,38 @@
 SELECT COUNT(@@GLOBAL.innodb_page_cleaners);
 --echo 1 Expected
 
-SELECT COUNT(@@innodb_page_cleaners);
+SELECT @@innodb_page_cleaners;
 --echo 1 Expected
 
---error ER_INCORRECT_GLOBAL_LOCAL_VAR
+SET @@GLOBAL.innodb_page_cleaners=2;
+--echo Expected to pass
+
+SELECT @@innodb_page_cleaners;
+--echo 2 Expected
+
 SET @@GLOBAL.innodb_page_cleaners=1;
---echo Expected error 'Read-only variable'
+--echo Expected to pass
+
+SELECT @@innodb_page_cleaners;
+--echo 1 Expected
+
+SET @@GLOBAL.innodb_page_cleaners=6;
+--echo Expected to pass
+
+SELECT @@innodb_page_cleaners;
+--echo 6 Expected
+
+SET @@GLOBAL.innodb_page_cleaners=4;
+--echo Expected to pass
+
+SELECT @@innodb_page_cleaners;
+--echo 4 Expected
+
+SET @@GLOBAL.innodb_page_cleaners=0;
+--echo Warning expected
+
+SELECT @@innodb_page_cleaners;
+--echo 1 Expected
 
 --Error ER_BAD_FIELD_ERROR
 SELECT innodb_page_cleaners = @@SESSION.innodb_page_cleaners;

storage/innobase/buf/buf0flu.cc

@@ -149,6 +149,8 @@ struct page_cleaner_t {
 						threads. */
 	os_event_t		is_finished;	/*!< event to signal that all
 						slots were finished. */
+	os_event_t		is_started;	/*!< event to signal that
+						thread is started/exiting */
 	volatile ulint		n_workers;	/*!< number of worker threads
 						in existence */
 	bool			requested;	/*!< true if requested pages
@@ -2728,6 +2730,7 @@ buf_flush_page_cleaner_init(void)
 
 	page_cleaner->is_requested = os_event_create("pc_is_requested");
 	page_cleaner->is_finished = os_event_create("pc_is_finished");
+	page_cleaner->is_started = os_event_create("pc_is_started");
 
 	page_cleaner->n_slots = static_cast<ulint>(srv_buf_pool_instances);
 
@@ -2757,6 +2760,7 @@ buf_flush_page_cleaner_close(void)
 
 	os_event_destroy(page_cleaner->is_finished);
 	os_event_destroy(page_cleaner->is_requested);
+	os_event_destroy(page_cleaner->is_started);
 
 	ut_free(page_cleaner);
 
@@ -3478,6 +3482,39 @@ DECLARE_THREAD(buf_flush_page_cleaner_coordinator)(void*)
 	OS_THREAD_DUMMY_RETURN;
 }
 
+/** Adjust thread count for page cleaner workers.
+@param[in]	new_cnt		Number of threads to be used */
+void
+buf_flush_set_page_cleaner_thread_cnt(ulong new_cnt)
+{
+	mutex_enter(&page_cleaner->mutex);
+
+	if (new_cnt > srv_n_page_cleaners) {
+		/* User has increased the number of page
+		cleaner threads. */
+		uint add = new_cnt - srv_n_page_cleaners;
+		srv_n_page_cleaners = new_cnt;
+		for (uint i = 0; i < add; i++) {
+			os_thread_id_t cleaner_thread_id;
+			os_thread_create(buf_flush_page_cleaner_worker, NULL, &cleaner_thread_id);
+		}
+	} else if (new_cnt < srv_n_page_cleaners) {
+		/* User has decreased the number of page
+		cleaner threads. */
+		srv_n_page_cleaners = new_cnt;
+	}
+
+	mutex_exit(&page_cleaner->mutex);
+
+	/* Wait until defined number of workers has started. */
+	while (page_cleaner->is_running &&
+	       page_cleaner->n_workers != (srv_n_page_cleaners - 1)) {
+		os_event_set(page_cleaner->is_requested);
+		os_event_reset(page_cleaner->is_started);
+		os_event_wait_time(page_cleaner->is_started, 1000000);
+	}
+}
+
 /******************************************************************//**
 Worker thread of page_cleaner.
 @return a dummy parameter */
@@ -3490,9 +3527,19 @@ DECLARE_THREAD(buf_flush_page_cleaner_worker)(
 			os_thread_create */
 {
 	my_thread_init();
+	os_thread_id_t cleaner_thread_id = os_thread_get_curr_id();
 
 	mutex_enter(&page_cleaner->mutex);
+	ulint thread_no = page_cleaner->n_workers;
 	page_cleaner->n_workers++;
+
+	DBUG_LOG("ib_buf", "Thread "
+		<< cleaner_thread_id
+		<< " started n_workers "
+		<< page_cleaner->n_workers << ".");
+
+	/* Signal that we have started */
+	os_event_set(page_cleaner->is_started);
 	mutex_exit(&page_cleaner->mutex);
 
 #ifdef UNIV_LINUX
@@ -3515,11 +3562,31 @@ DECLARE_THREAD(buf_flush_page_cleaner_worker)(
 			break;
 		}
 
+		ut_ad(srv_n_page_cleaners >= 1);
+
+		/* If number of page cleaner threads is decreased
+		exit those that are not anymore needed. */
+		if (srv_shutdown_state == SRV_SHUTDOWN_NONE &&
+		    thread_no >= (srv_n_page_cleaners - 1)) {
+			DBUG_LOG("ib_buf", "Exiting "
+				<< thread_no
+				<< " page cleaner worker thread_id "
+				<< os_thread_pf(cleaner_thread_id)
+				<< " total threads " << srv_n_page_cleaners << ".");
+			break;
+		}
+
 		pc_flush_slot();
 	}
 
 	mutex_enter(&page_cleaner->mutex);
 	page_cleaner->n_workers--;
+
+	DBUG_LOG("ib_buf", "Thread " << cleaner_thread_id
+		<< " exiting n_workers " << page_cleaner->n_workers<< ".");
+
+	/* Signal that we have stopped */
+	os_event_set(page_cleaner->is_started);
 	mutex_exit(&page_cleaner->mutex);
 
 	my_thread_end();

storage/innobase/handler/ha_innodb.cc

@@ -19984,10 +19984,20 @@ static MYSQL_SYSVAR_STR(log_group_home_dir, srv_log_group_home_dir,
   PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_READONLY,
   "Path to InnoDB log files.", NULL, NULL, NULL);
 
+/** Update innodb_page_cleaners.
+@param[in]	save	the new value of innodb_page_cleaners */
+static
+void
+innodb_page_cleaners_threads_update(THD*, struct st_mysql_sys_var*, void*, const void *save)
+{
+	buf_flush_set_page_cleaner_thread_cnt(*static_cast<const ulong*>(save));
+}
+
 static MYSQL_SYSVAR_ULONG(page_cleaners, srv_n_page_cleaners,
-  PLUGIN_VAR_OPCMDARG | PLUGIN_VAR_READONLY,
+  PLUGIN_VAR_RQCMDARG,
   "Page cleaner threads can be from 1 to 64. Default is 4.",
-  NULL, NULL, 4, 1, 64, 0);
+  NULL,
+  innodb_page_cleaners_threads_update, 4, 1, 64, 0);
 
 static MYSQL_SYSVAR_DOUBLE(max_dirty_pages_pct, srv_max_buf_pool_modified_pct,
   PLUGIN_VAR_RQCMDARG,

storage/innobase/include/buf0flu.h

@@ -243,6 +243,12 @@ DECLARE_THREAD(buf_flush_page_cleaner_coordinator)(
 /*===============================================*/
 	void*	arg);		/*!< in: a dummy parameter required by
 				os_thread_create */
+
+/** Adjust thread count for page cleaner workers.
+@param[in]	new_cnt		Number of threads to be used */
+void
+buf_flush_set_page_cleaner_thread_cnt(ulong new_cnt);
+
 /******************************************************************//**
 Worker thread of page_cleaner.
 @return a dummy parameter */

storage/innobase/srv/srv0start.cc

@@ -1868,9 +1868,10 @@ innobase_start_or_create_for_mysql()
 		os_thread_create(buf_flush_page_cleaner_coordinator,
 				 NULL, NULL);
 
-		for (i = 1; i < srv_n_page_cleaners; ++i) {
-			os_thread_create(buf_flush_page_cleaner_worker,
-					 NULL, NULL);
+		/* Create page cleaner workers if needed. For example
+		mariabackup could set srv_n_page_cleaners = 0. */
+		if (srv_n_page_cleaners > 1) {
+			buf_flush_set_page_cleaner_thread_cnt(srv_n_page_cleaners);
 		}
 
 #ifdef UNIV_LINUX

sysvars_aria,32bit.rdiff

+--- sysvars_aria.result	2015-01-09 11:49:32.000000000 +0100
++++ sysvars_aria,32bit.result	2015-01-09 17:30:11.000000000 +0100
+@@ -7,7 +7,7 @@
+ GLOBAL_VALUE_ORIGIN	COMPILE-TIME
+ DEFAULT_VALUE	8192
+ VARIABLE_SCOPE	GLOBAL
+-VARIABLE_TYPE	BIGINT UNSIGNED
++VARIABLE_TYPE	INT UNSIGNED
+ VARIABLE_COMMENT	Block size to be used for Aria index pages.
+ NUMERIC_MIN_VALUE	1024
+ NUMERIC_MAX_VALUE	32768
+@@ -21,7 +21,7 @@
+ GLOBAL_VALUE_ORIGIN	COMPILE-TIME
+ DEFAULT_VALUE	30
+ VARIABLE_SCOPE	GLOBAL
+-VARIABLE_TYPE	BIGINT UNSIGNED
++VARIABLE_TYPE	INT UNSIGNED
+ VARIABLE_COMMENT	Interval between tries to do an automatic checkpoints. In seconds; 0 means 'no automatic checkpoints' which makes sense only for testing.
+ NUMERIC_MIN_VALUE	0
+ NUMERIC_MAX_VALUE	4294967295
+@@ -35,7 +35,7 @@
+ GLOBAL_VALUE_ORIGIN	COMPILE-TIME
+ DEFAULT_VALUE	1048576
+ VARIABLE_SCOPE	GLOBAL
+-VARIABLE_TYPE	BIGINT UNSIGNED
++VARIABLE_TYPE	INT UNSIGNED
+ VARIABLE_COMMENT	Number of bytes that the transaction log has to grow between checkpoints before a new checkpoint is written to the log.
+ NUMERIC_MIN_VALUE	0
+ NUMERIC_MAX_VALUE	4294967295
+@@ -63,7 +63,7 @@
+ GLOBAL_VALUE_ORIGIN	COMPILE-TIME
+ DEFAULT_VALUE	0
+ VARIABLE_SCOPE	GLOBAL
+-VARIABLE_TYPE	BIGINT UNSIGNED
++VARIABLE_TYPE	INT UNSIGNED
+ VARIABLE_COMMENT	Number of consecutive log recovery failures after which logs will be automatically deleted to cure the problem; 0 (the default) disables the feature.
+ NUMERIC_MIN_VALUE	0
+ NUMERIC_MAX_VALUE	255
+@@ -91,7 +91,7 @@
+ GLOBAL_VALUE_ORIGIN	COMPILE-TIME
+ DEFAULT_VALUE	0
+ VARIABLE_SCOPE	GLOBAL
+-VARIABLE_TYPE	BIGINT UNSIGNED
++VARIABLE_TYPE	INT UNSIGNED
+ VARIABLE_COMMENT	Interval between commite in microseconds (1/1000000c). 0 stands for no waiting for other threads to come and do a commit in "hard" mode and no sync()/commit at all in "soft" mode.  Option has only an effect if aria_group_commit is used
+ NUMERIC_MIN_VALUE	0
+ NUMERIC_MAX_VALUE	4294967295
+@@ -105,7 +105,7 @@
+ GLOBAL_VALUE_ORIGIN	CONFIG
+ DEFAULT_VALUE	1073741824
+ VARIABLE_SCOPE	GLOBAL
+-VARIABLE_TYPE	BIGINT UNSIGNED
++VARIABLE_TYPE	INT UNSIGNED
+ VARIABLE_COMMENT	Limit for transaction log size
+ NUMERIC_MIN_VALUE	8388608
+ NUMERIC_MAX_VALUE	4294967295
+@@ -147,10 +147,10 @@
+ GLOBAL_VALUE_ORIGIN	COMPILE-TIME
+ DEFAULT_VALUE	300
+ VARIABLE_SCOPE	GLOBAL
+-VARIABLE_TYPE	BIGINT UNSIGNED
++VARIABLE_TYPE	INT UNSIGNED
+ VARIABLE_COMMENT	This characterizes the number of hits a hot block has to be untouched until it is considered aged enough to be downgraded to a warm block. This specifies the percentage ratio of that number of hits to the total number of blocks in the page cache.
+ NUMERIC_MIN_VALUE	100
+-NUMERIC_MAX_VALUE	18446744073709551615
++NUMERIC_MAX_VALUE	4294967295
+ NUMERIC_BLOCK_SIZE	100
+ ENUM_VALUE_LIST	NULL
+ READ_ONLY	NO
+@@ -175,7 +175,7 @@
+ GLOBAL_VALUE_ORIGIN	COMPILE-TIME
+ DEFAULT_VALUE	100
+ VARIABLE_SCOPE	GLOBAL
+-VARIABLE_TYPE	BIGINT UNSIGNED
++VARIABLE_TYPE	INT UNSIGNED
+ VARIABLE_COMMENT	The minimum percentage of warm blocks in key cache
+ NUMERIC_MIN_VALUE	1
+ NUMERIC_MAX_VALUE	100
+@@ -189,7 +189,7 @@
+ GLOBAL_VALUE_ORIGIN	COMPILE-TIME
+ DEFAULT_VALUE	512
+ VARIABLE_SCOPE	GLOBAL
+-VARIABLE_TYPE	BIGINT UNSIGNED
++VARIABLE_TYPE	INT UNSIGNED
+ VARIABLE_COMMENT	Number of hash buckets for open and changed files.  If you have a lot of Aria files open you should increase this for faster flush of changes. A good value is probably 1/10 of number of possible open Aria files.
+ NUMERIC_MIN_VALUE	128
+ NUMERIC_MAX_VALUE	16384
+@@ -231,7 +231,7 @@
+ GLOBAL_VALUE_ORIGIN	COMPILE-TIME
+ DEFAULT_VALUE	1
+ VARIABLE_SCOPE	SESSION
+-VARIABLE_TYPE	BIGINT UNSIGNED
++VARIABLE_TYPE	INT UNSIGNED
+ VARIABLE_COMMENT	Number of threads to use when repairing Aria tables. The value of 1 disables parallel repair.
+ NUMERIC_MIN_VALUE	1
+ NUMERIC_MAX_VALUE	128
+@@ -248,7 +248,7 @@
+ VARIABLE_TYPE	BIGINT UNSIGNED
+ VARIABLE_COMMENT	The buffer that is allocated when sorting the index when doing a REPAIR or when creating indexes with CREATE INDEX or ALTER TABLE.
+ NUMERIC_MIN_VALUE	4096
+-NUMERIC_MAX_VALUE	18446744073709551615
++NUMERIC_MAX_VALUE	4294967295
+ NUMERIC_BLOCK_SIZE	1
+ ENUM_VALUE_LIST	NULL
+ READ_ONLY	NO

sysvars_debug,32bit.rdiff

+--- suite/sys_vars/r/sysvars_debug.result	2017-09-14 10:37:46.000000000 +0000
++++ suite/sys_vars/r/sysvars_debug,32bit.reject	2017-09-26 13:15:14.197012523 +0000
+@@ -21,7 +21,7 @@
+ GLOBAL_VALUE_ORIGIN	CONFIG
+ DEFAULT_VALUE	0
+ VARIABLE_SCOPE	GLOBAL
+-VARIABLE_TYPE	BIGINT UNSIGNED
++VARIABLE_TYPE	INT UNSIGNED
+ VARIABLE_COMMENT	Extra sleep (in microseconds) to add to binlog fsync(), for debugging
+ NUMERIC_MIN_VALUE	0
+ NUMERIC_MAX_VALUE	4294967295

sysvars_wsrep,32bit.rdiff

+--- suite/sys_vars/r/sysvars_wsrep.result	2014-10-10 13:33:55.000000000 +0300
++++ suite/sys_vars/r/sysvars_wsrep,32bit.reject	2014-10-10 19:38:09.000000000 +0300
+@@ -245,7 +245,7 @@
+ GLOBAL_VALUE_ORIGIN	COMPILE-TIME
+ DEFAULT_VALUE	131072
+ VARIABLE_SCOPE	GLOBAL
+-VARIABLE_TYPE	BIGINT UNSIGNED
++VARIABLE_TYPE	INT UNSIGNED
+ VARIABLE_COMMENT	Max number of rows in write set
+ NUMERIC_MIN_VALUE	1
+ NUMERIC_MAX_VALUE	1048576
+@@ -259,7 +259,7 @@
+ GLOBAL_VALUE_ORIGIN	COMPILE-TIME
+ DEFAULT_VALUE	1073741824
+ VARIABLE_SCOPE	GLOBAL
+-VARIABLE_TYPE	BIGINT UNSIGNED
++VARIABLE_TYPE	INT UNSIGNED
+ VARIABLE_COMMENT	Max write set size (bytes)
+ NUMERIC_MIN_VALUE	1024
+ NUMERIC_MAX_VALUE	4294901759
+@@ -273,7 +273,7 @@
+ GLOBAL_VALUE_ORIGIN	COMPILE-TIME
+ DEFAULT_VALUE	0
+ VARIABLE_SCOPE	GLOBAL
+-VARIABLE_TYPE	BIGINT UNSIGNED
++VARIABLE_TYPE	INT UNSIGNED
+ VARIABLE_COMMENT	mysql replication group commit 
+ NUMERIC_MIN_VALUE	0
+ NUMERIC_MAX_VALUE	1000
+@@ -455,7 +455,7 @@
+ GLOBAL_VALUE_ORIGIN	COMPILE-TIME
+ DEFAULT_VALUE	1
+ VARIABLE_SCOPE	SESSION
+-VARIABLE_TYPE	BIGINT UNSIGNED
++VARIABLE_TYPE	INT UNSIGNED
+ VARIABLE_COMMENT	Max number of times to retry a failed autocommit statement
+ NUMERIC_MIN_VALUE	0
+ NUMERIC_MAX_VALUE	10000
+@@ -483,7 +483,7 @@
+ GLOBAL_VALUE_ORIGIN	COMPILE-TIME
+ DEFAULT_VALUE	1
+ VARIABLE_SCOPE	GLOBAL
+-VARIABLE_TYPE	BIGINT UNSIGNED
++VARIABLE_TYPE	INT UNSIGNED
+ VARIABLE_COMMENT	Number of slave appliers to launch
+ NUMERIC_MIN_VALUE	1
+ NUMERIC_MAX_VALUE	512