MDEV-26790 InnoDB read-ahead may cause page writes

buf_LRU_get_free_block(): Replace the Boolean parameter with a
ternary parameter, so that have_no_mutex_soft can be specified
reduce the chances of initiating page eviction flushing in read-ahead.

buf_read_acquire(): Invoke buf_LRU_get_free_block(have_no_mutex_soft)
and check in each caller for a nullptr return value.

storage/innobase/buf/buf0buddy.cc

 /*****************************************************************************
 
 Copyright (c) 2006, 2016, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2018, 2021, MariaDB Corporation.
+Copyright (c) 2018, 2022, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -454,7 +454,7 @@ byte *buf_buddy_alloc_low(ulint i, bool *lru)
 	}
 
 	/* Try replacing an uncompressed page in the buffer pool. */
-	block = buf_LRU_get_free_block(true);
+	block = buf_LRU_get_free_block(have_mutex);
 	if (lru) {
 		*lru = true;
 	}

storage/innobase/buf/buf0buf.cc

@@ -2416,7 +2416,7 @@ buf_page_get_low(
 			goto loop;
 		}
 
-		buf_block_t *new_block = buf_LRU_get_free_block(false);
+		buf_block_t *new_block = buf_LRU_get_free_block(have_no_mutex);
 		buf_block_init_low(new_block);
 
 wait_for_unfix:

storage/innobase/buf/buf0lru.cc

@@ -386,14 +386,15 @@ we put it to free list to be used.
   * scan whole LRU list
   * scan LRU list even if buf_pool.try_LRU_scan is not set
 
-@param have_mutex  whether buf_pool.mutex is already being held
-@return the free control block, in state BUF_BLOCK_MEMORY */
-buf_block_t *buf_LRU_get_free_block(bool have_mutex)
+@param get  how to allocate the block
+@return the free control block, in state BUF_BLOCK_MEMORY
+@retval nullptr if get==have_no_mutex_soft and memory was not available */
+buf_block_t* buf_LRU_get_free_block(buf_LRU_get get)
 {
 	ulint		n_iterations	= 0;
 	ulint		flush_failures	= 0;
 	MONITOR_INC(MONITOR_LRU_GET_FREE_SEARCH);
-	if (have_mutex) {
+	if (UNIV_UNLIKELY(get == have_mutex)) {
 		mysql_mutex_assert_owner(&buf_pool.mutex);
 		goto got_mutex;
 	}
@@ -405,13 +406,14 @@ buf_block_t *buf_LRU_get_free_block(bool have_mutex)
 	DBUG_EXECUTE_IF("ib_lru_force_no_free_page",
 		if (!buf_lru_free_blocks_error_printed) {
 			n_iterations = 21;
+			block = nullptr;
 			goto not_found;});
 
 retry:
 	/* If there is a block in the free list, take it */
 	if ((block = buf_LRU_get_free_only()) != nullptr) {
 got_block:
-		if (!have_mutex) {
+		if (UNIV_LIKELY(get != have_mutex)) {
 			mysql_mutex_unlock(&buf_pool.mutex);
 		}
 		block->page.zip.clear();
@@ -435,6 +437,11 @@ buf_block_t *buf_LRU_get_free_block(bool have_mutex)
 		buf_pool.try_LRU_scan = false;
 	}
 
+	if (get == have_no_mutex_soft) {
+		mysql_mutex_unlock(&buf_pool.mutex);
+		return nullptr;
+	}
+
 	for (;;) {
 		if ((block = buf_LRU_get_free_only()) != nullptr) {
 			goto got_block;

storage/innobase/buf/buf0rea.cc

@@ -272,7 +272,7 @@ buf_read_page_low(
 /** Acquire a buffer block. */
 static buf_block_t *buf_read_acquire()
 {
-  return buf_LRU_get_free_block(false);
+  return buf_LRU_get_free_block(have_no_mutex_soft);
 }
 
 /** Free a buffer block if needed. */
@@ -341,7 +341,9 @@ ulint buf_read_ahead_random(const page_id_t page_id, ulint zip_size)
     goto no_read_ahead;
 
   /* Read all the suitable blocks within the area */
-  buf_block_t *block= zip_size ? nullptr : buf_read_acquire();
+  buf_block_t *block= nullptr;
+  if (!zip_size && !(block= buf_read_acquire()))
+    goto no_read_ahead;
 
   for (page_id_t i= low; i < high; ++i)
   {
@@ -354,8 +356,8 @@ ulint buf_read_ahead_random(const page_id_t page_id, ulint zip_size)
     {
       count++;
       ut_ad(!block);
-      if (!zip_size)
-        block= buf_read_acquire();
+      if (!zip_size && !(block= buf_read_acquire()))
+        break;
     }
   }
 
@@ -398,7 +400,9 @@ dberr_t buf_read_page(const page_id_t page_id, ulint zip_size,
     return DB_TABLESPACE_DELETED;
   }
 
-  buf_block_t *block= zip_size ? nullptr : buf_LRU_get_free_block(false);
+  buf_block_t *block= zip_size
+    ? nullptr
+    : buf_LRU_get_free_block(have_no_mutex);
 
   /* Our caller should already have ensured that the page does not
   exist in buf_pool.page_hash. */
@@ -428,11 +432,14 @@ void buf_read_page_background(fil_space_t *space, const page_id_t page_id,
   buf_pool_t::hash_chain &chain= buf_pool.page_hash.cell_get(page_id.fold());
   if (buf_pool.page_hash_contains(page_id, chain))
   {
+  skip:
     space->release();
     return;
   }
 
-  buf_block_t *block= zip_size ? nullptr : buf_read_acquire();
+  buf_block_t *block= nullptr;
+  if (!zip_size && !(block= buf_read_acquire()))
+    goto skip;
 
   dberr_t err;
   if (buf_read_page_low(page_id, zip_size, chain, &err, space, block))
@@ -581,7 +588,9 @@ ulint buf_read_ahead_linear(const page_id_t page_id, ulint zip_size)
   }
 
   /* If we got this far, read-ahead can be sensible: do it */
-  buf_block_t *block= zip_size ? nullptr : buf_read_acquire();
+  buf_block_t *block= nullptr;
+  if (!zip_size && !(block= buf_read_acquire()))
+    goto fail;
 
   count= 0;
   for (; new_low != new_high_1; ++new_low)
@@ -595,8 +604,8 @@ ulint buf_read_ahead_linear(const page_id_t page_id, ulint zip_size)
     {
       count++;
       ut_ad(!block);
-      if (!zip_size)
-        block= buf_read_acquire();
+      if (!zip_size && !(block= buf_read_acquire()))
+        break;
     }
   }
 
@@ -635,7 +644,7 @@ void buf_read_recv_pages(uint32_t space_id, st_::span<uint32_t> page_nos)
 	}
 
 	const ulint zip_size = space->zip_size() | 1;
-	buf_block_t* block = buf_LRU_get_free_block(false);
+	buf_block_t* block = buf_LRU_get_free_block(have_no_mutex);
 
 	for (ulint i = 0; i < page_nos.size(); i++) {
 
@@ -672,7 +681,7 @@ void buf_read_recv_pages(uint32_t space_id, st_::span<uint32_t> page_nos)
 		if (buf_read_page_low(cur_page_id, zip_size, chain, &err, space,
 				      block)) {
 			ut_ad(!block);
-			block = buf_LRU_get_free_block(false);
+			block = buf_LRU_get_free_block(have_no_mutex);
 		}
 
 		if (err != DB_SUCCESS) {

storage/innobase/fsp/fsp0fsp.cc

@@ -499,7 +499,7 @@ dberr_t fsp_header_init(fil_space_t *space, uint32_t size, mtr_t *mtr)
 	const page_id_t page_id(space->id, 0);
 	const ulint zip_size = space->zip_size();
 
-	buf_block_t *free_block = buf_LRU_get_free_block(false);
+	buf_block_t *free_block = buf_LRU_get_free_block(have_no_mutex);
 
 	mtr->x_lock_space(space);
 
@@ -833,7 +833,7 @@ fsp_fill_free_list(
 
       if (i)
       {
-        buf_block_t *f= buf_LRU_get_free_block(false);
+        buf_block_t *f= buf_LRU_get_free_block(have_no_mutex);
         buf_block_t *block= buf_page_create(space, static_cast<uint32_t>(i),
                                             zip_size, mtr, f);
         if (UNIV_UNLIKELY(block != f))
@@ -845,7 +845,7 @@ fsp_fill_free_list(
 
       if (space->purpose != FIL_TYPE_TEMPORARY)
       {
-        buf_block_t *f= buf_LRU_get_free_block(false);
+        buf_block_t *f= buf_LRU_get_free_block(have_no_mutex);
         buf_block_t *block=
           buf_page_create(space, static_cast<uint32_t>(i + 1),
                           zip_size, mtr, f);
@@ -1053,7 +1053,7 @@ fsp_page_create(fil_space_t *space, page_no_t offset, mtr_t *mtr)
     }
   }
 
-  free_block= buf_LRU_get_free_block(false);
+  free_block= buf_LRU_get_free_block(have_no_mutex);
 got_free_block:
   block= buf_page_create(space, static_cast<uint32_t>(offset),
                          space->zip_size(), mtr, free_block);

storage/innobase/include/buf0buf.inl

@@ -90,7 +90,7 @@ inline bool buf_page_peek_if_too_old(const buf_page_t *bpage)
 @return own: the allocated block, in state BUF_BLOCK_MEMORY */
 inline buf_block_t *buf_block_alloc()
 {
-  return buf_LRU_get_free_block(false);
+  return buf_LRU_get_free_block(have_no_mutex);
 }
 
 /********************************************************************//**

storage/innobase/include/buf0lru.h

 /*****************************************************************************
 
 Copyright (c) 1995, 2016, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2017, 2021, MariaDB Corporation.
+Copyright (c) 2017, 2022, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -62,6 +62,17 @@ bool buf_LRU_scan_and_free_block(ulint limit= ULINT_UNDEFINED);
 @retval	NULL	if the free list is empty */
 buf_block_t* buf_LRU_get_free_only();
 
+/** How to acquire a block */
+enum buf_LRU_get {
+  /** The caller is not holding buf_pool.mutex */
+  have_no_mutex= 0,
+  /** The caller is holding buf_pool.mutex */
+  have_mutex,
+  /** The caller is not holding buf_pool.mutex and is OK if a block
+  cannot be allocated. */
+  have_no_mutex_soft
+};
+
 /** Get a block from the buf_pool.free list.
 If the list is empty, blocks will be moved from the end of buf_pool.LRU
 to buf_pool.free.
@@ -83,9 +94,10 @@ we put it to free list to be used.
   * scan whole LRU list
   * scan LRU list even if buf_pool.try_LRU_scan is not set
 
-@param have_mutex  whether buf_pool.mutex is already being held
-@return the free control block, in state BUF_BLOCK_MEMORY */
-buf_block_t* buf_LRU_get_free_block(bool have_mutex)
+@param get  how to allocate the block
+@return the free control block, in state BUF_BLOCK_MEMORY
+@retval nullptr if get==have_no_mutex_soft and memory was not available */
+buf_block_t* buf_LRU_get_free_block(buf_LRU_get get)
 	MY_ATTRIBUTE((malloc,warn_unused_result));
 
 /** @return whether the unzip_LRU list should be used for evicting a victim

storage/innobase/log/log0recv.cc

@@ -726,7 +726,7 @@ static struct
   {
 retry:
     bool fail= false;
-    buf_block_t *free_block= buf_LRU_get_free_block(false);
+    buf_block_t *free_block= buf_LRU_get_free_block(have_no_mutex);
     mysql_mutex_lock(&recv_sys.mutex);
 
     for (auto d= defers.begin(); d != defers.end(); )
@@ -3284,7 +3284,7 @@ inline buf_block_t *recv_sys_t::recover_low(const page_id_t page_id,
 @retval nullptr if the page cannot be initialized based on log records */
 buf_block_t *recv_sys_t::recover_low(const page_id_t page_id)
 {
-  buf_block_t *free_block= buf_LRU_get_free_block(false);
+  buf_block_t *free_block= buf_LRU_get_free_block(have_no_mutex);
   buf_block_t *block= nullptr;
 
   mysql_mutex_lock(&mutex);
@@ -3404,7 +3404,7 @@ void recv_sys_t::apply(bool last_batch)
 
     fil_system.extend_to_recv_size();
 
-    buf_block_t *free_block= buf_LRU_get_free_block(false);
+    buf_block_t *free_block= buf_LRU_get_free_block(have_no_mutex);
 
     for (map::iterator p= pages.begin(); p != pages.end(); )
     {
@@ -3451,7 +3451,7 @@ void recv_sys_t::apply(bool last_batch)
         {
 next_free_block:
           mysql_mutex_unlock(&mutex);
-          free_block= buf_LRU_get_free_block(false);
+          free_block= buf_LRU_get_free_block(have_no_mutex);
           mysql_mutex_lock(&mutex);
           break;
         }