MDEV-24537 innodb_max_dirty_pages_pct_lwm=0 lost its special meaning

In commit 3a9a3be1c64b14c05648e87ebe0f1dd96457de41 (MDEV-23855)
some previous logic was replaced with the condition
dirty_pct < srv_max_dirty_pages_pct_lwm, which caused
the default value of the parameter innodb_max_dirty_pages_pct_lwm=0
to lose its special meaning: 'refer to innodb_max_dirty_pages_pct instead'.

This implicit special meaning was visible in the function
af_get_pct_for_dirty(), which was removed in
commit f0c295e2de8c074c2ca72e19ff06e1d0e3ee6d2b (MDEV-24369).

page_cleaner_flush_pages_recommendation(): Restore the special
meaning that was removed in MDEV-24369.

buf_flush_page_cleaner(): If srv_max_dirty_pages_pct_lwm==0.0,
refer to srv_max_buf_pool_modified_pct. This fixes the observed
performance regression due to excessive page flushing.

buf_pool_t::page_cleaner_wakeup(): Revise the wakeup condition.

innodb_init(): Do initialize srv_max_io_capacity in Mariabackup.
It was previously constantly 0, which caused mariadb-backup --prepare
to hang in buf_flush_sync(), making no progress.

5 files changed, 30 insertions, 15 deletions

diff --git a/extra/mariabackup/xtrabackup.cc b/extra/mariabackup/xtrabackup.cc
index 217976e637c..b8cdf4cd9db 100644
--- a/extra/mariabackup/xtrabackup.cc
+++ b/extra/mariabackup/xtrabackup.cc
@@ -4,7 +4,7 @@ MariaBackup: hot backup tool for InnoDB
 Originally Created 3/3/2009 Yasufumi Kinoshita
 Written by Alexey Kopytov, Aleksandr Kuzminsky, Stewart Smith, Vadim Tkachenko,
 Yasufumi Kinoshita, Ignacio Nin and Baron Schwartz.
-(c) 2017, 2020, MariaDB Corporation.
+(c) 2017, 2021, MariaDB Corporation.
 Portions written by Marko Mäkelä.
 
 This program is free software; you can redistribute it and/or modify
@@ -2183,6 +2183,14 @@ error:
 static bool innodb_init()
 {
 	bool create_new_db = false;
+
+	if (srv_io_capacity >= SRV_MAX_IO_CAPACITY_LIMIT / 2) {
+		/* Avoid overflow. */
+		srv_max_io_capacity = SRV_MAX_IO_CAPACITY_LIMIT;
+	} else {
+		srv_max_io_capacity = std::max(2 * srv_io_capacity, 2000UL);
+	}
+
 	/* Check if the data files exist or not. */
 	dberr_t err = srv_sys_space.check_file_spec(&create_new_db, 5U << 20);
 
diff --git a/mysql-test/suite/sys_vars/r/sysvars_innodb.result b/mysql-test/suite/sys_vars/r/sysvars_innodb.result
index 591471cbbff..2a7d7b9a246 100644
--- a/mysql-test/suite/sys_vars/r/sysvars_innodb.result
+++ b/mysql-test/suite/sys_vars/r/sysvars_innodb.result
@@ -1322,7 +1322,7 @@ SESSION_VALUE	NULL
 DEFAULT_VALUE	0.000000
 VARIABLE_SCOPE	GLOBAL
 VARIABLE_TYPE	DOUBLE
-VARIABLE_COMMENT	Percentage of dirty pages at which flushing kicks in.
+VARIABLE_COMMENT	Percentage of dirty pages at which flushing kicks in. The value 0 (default) means 'refer to innodb_max_dirty_pages_pct'.
 NUMERIC_MIN_VALUE	0
 NUMERIC_MAX_VALUE	99.999
 NUMERIC_BLOCK_SIZE	NULL
diff --git a/storage/innobase/buf/buf0flu.cc b/storage/innobase/buf/buf0flu.cc
index 81095a6d0d2..934feadb437 100644
--- a/storage/innobase/buf/buf0flu.cc
+++ b/storage/innobase/buf/buf0flu.cc
@@ -1,7 +1,7 @@
 /*****************************************************************************
 
 Copyright (c) 1995, 2017, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2013, 2020, MariaDB Corporation.
+Copyright (c) 2013, 2021, MariaDB Corporation.
 Copyright (c) 2013, 2014, Fusion-io
 
 This program is free software; you can redistribute it and/or modify it under
@@ -129,11 +129,13 @@ static void buf_flush_validate_skip()
 /** Wake up the page cleaner if needed */
 inline void buf_pool_t::page_cleaner_wakeup()
 {
-  if (page_cleaner_idle() &&
-      (srv_max_dirty_pages_pct_lwm == 0.0 ||
-       srv_max_dirty_pages_pct_lwm <=
-       double(UT_LIST_GET_LEN(buf_pool.flush_list)) * 100.0 /
-       double(UT_LIST_GET_LEN(buf_pool.LRU) + UT_LIST_GET_LEN(buf_pool.free))))
+  if (!page_cleaner_idle())
+    return;
+  double dirty_pct= double(UT_LIST_GET_LEN(buf_pool.flush_list)) * 100.0 /
+    double(UT_LIST_GET_LEN(buf_pool.LRU) + UT_LIST_GET_LEN(buf_pool.free));
+  double pct_lwm= srv_max_dirty_pages_pct_lwm;
+  if ((pct_lwm != 0.0 && pct_lwm <= dirty_pct) ||
+      srv_max_buf_pool_modified_pct <= dirty_pct)
   {
     page_cleaner_is_idle= false;
     mysql_cond_signal(&do_flush_list);
@@ -1989,7 +1991,9 @@ static ulint page_cleaner_flush_pages_recommendation(ulint last_pages_in,
 		sum_pages = 0;
 	}
 
-	const ulint pct_for_dirty = static_cast<ulint>
+	const ulint pct_for_dirty = srv_max_dirty_pages_pct_lwm == 0
+		? (dirty_pct >= max_pct ? 100 : 0)
+		: static_cast<ulint>
 		(max_pct > 0.0 ? dirty_pct / max_pct : dirty_pct);
 	ulint pct_total = std::max(pct_for_dirty, pct_for_lsn);
 
@@ -2129,7 +2133,11 @@ unemployed:
     const double dirty_pct= double(dirty_blocks) * 100.0 /
       double(UT_LIST_GET_LEN(buf_pool.LRU) + UT_LIST_GET_LEN(buf_pool.free));
 
-    if (dirty_pct < srv_max_dirty_pages_pct_lwm && !lsn_limit)
+    if (lsn_limit);
+    else if (dirty_pct < srv_max_buf_pool_modified_pct)
+      goto unemployed;
+    else if (srv_max_dirty_pages_pct_lwm == 0.0 ||
+             dirty_pct < srv_max_dirty_pages_pct_lwm)
       goto unemployed;
 
     const lsn_t oldest_lsn= buf_pool.get_oldest_modified()
diff --git a/storage/innobase/handler/ha_innodb.cc b/storage/innobase/handler/ha_innodb.cc
index 227b63674b9..92cfd81e97b 100644
--- a/storage/innobase/handler/ha_innodb.cc
+++ b/storage/innobase/handler/ha_innodb.cc
@@ -19032,7 +19032,8 @@ static MYSQL_SYSVAR_DOUBLE(max_dirty_pages_pct, srv_max_buf_pool_modified_pct,
 static MYSQL_SYSVAR_DOUBLE(max_dirty_pages_pct_lwm,
   srv_max_dirty_pages_pct_lwm,
   PLUGIN_VAR_RQCMDARG,
-  "Percentage of dirty pages at which flushing kicks in.",
+  "Percentage of dirty pages at which flushing kicks in. "
+  "The value 0 (default) means 'refer to innodb_max_dirty_pages_pct'.",
   NULL, innodb_max_dirty_pages_pct_lwm_update, 0, 0, 99.999, 0);
 
 static MYSQL_SYSVAR_DOUBLE(adaptive_flushing_lwm,
diff --git a/storage/innobase/include/srv0srv.h b/storage/innobase/include/srv0srv.h
index 7c90c7f8864..adb679dfa3c 100644
--- a/storage/innobase/include/srv0srv.h
+++ b/storage/innobase/include/srv0srv.h
@@ -3,7 +3,7 @@
 Copyright (c) 1995, 2017, Oracle and/or its affiliates. All rights reserved.
 Copyright (c) 2008, 2009, Google Inc.
 Copyright (c) 2009, Percona Inc.
-Copyright (c) 2013, 2020, MariaDB Corporation.
+Copyright (c) 2013, 2021, MariaDB Corporation.
 
 Portions of this file contain modifications contributed and copyrighted by
 Google, Inc. Those modifications are gratefully acknowledged and are described
@@ -373,7 +373,7 @@ extern ulong	srv_innodb_stats_method;
 
 extern ulint	srv_max_n_open_files;
 
-extern double	srv_max_dirty_pages_pct;
+extern double	srv_max_buf_pool_modified_pct;
 extern double	srv_max_dirty_pages_pct_lwm;
 
 extern double	srv_adaptive_flushing_lwm;
@@ -400,10 +400,8 @@ extern my_bool			srv_stats_sample_traditional;
 extern my_bool	srv_use_doublewrite_buf;
 extern ulong	srv_checksum_algorithm;
 
-extern double	srv_max_buf_pool_modified_pct;
 extern my_bool	srv_force_primary_key;
 
-extern double	srv_max_buf_pool_modified_pct;
 extern ulong	srv_max_purge_lag;
 extern ulong	srv_max_purge_lag_delay;