MDEV-15058: Remove buf_pool_get_dirty_pages_count()

Starting with commit 1a6f708e
the function buf_pool_get_dirty_pages_count() is only used
in a debug check. It was dead code for non-debug builds.

buf_flush_dirty_pages(): Perform the debug check inline,
and replace the assertion
	ut_ad(first || buf_pool_get_dirty_pages_count(id) == 0);
with another one that is executed while holding the mutexes:
	ut_ad(id != bpage->id.space());

storage/innobase/buf/buf0flu.cc

@@ -3228,34 +3228,3 @@ void buf_flush_validate()
 }
 
 #endif /* UNIV_DEBUG || UNIV_BUF_DEBUG */
-
-/** Determine the number of dirty pages in a tablespace.
-@param[in]	id		tablespace identifier
-@return number of dirty pages */
-ulint buf_pool_get_dirty_pages_count(ulint id)
-{
-	ulint		count = 0;
-
-	mutex_enter(&buf_pool->mutex);
-	mutex_enter(&buf_pool->flush_list_mutex);
-
-	buf_page_t*	bpage;
-
-	for (bpage = UT_LIST_GET_FIRST(buf_pool->flush_list);
-	     bpage != 0;
-	     bpage = UT_LIST_GET_NEXT(list, bpage)) {
-
-		ut_ad(buf_page_in_file(bpage));
-		ut_ad(bpage->in_flush_list);
-		ut_ad(bpage->oldest_modification > 0);
-
-		if (id == bpage->id.space()) {
-			++count;
-		}
-	}
-
-	mutex_exit(&buf_pool->flush_list_mutex);
-	mutex_exit(&buf_pool->mutex);
-
-	return(count);
-}

storage/innobase/buf/buf0lru.cc

@@ -604,22 +604,34 @@ as they age and move towards the tail of the LRU list.
 @param[in]	first		first page to be flushed or evicted */
 static void buf_flush_dirty_pages(ulint id, bool flush, ulint first)
 {
-	for (;;) {
-		mutex_enter(&buf_pool->mutex);
-		bool freed = buf_flush_or_remove_pages(id, flush, first);
-		mutex_exit(&buf_pool->mutex);
-
-		ut_d(buf_flush_validate());
-
-		if (freed) {
-			break;
-		}
+  mutex_enter(&buf_pool->mutex);
+  while (!buf_flush_or_remove_pages(id, flush, first))
+  {
+    mutex_exit(&buf_pool->mutex);
+    ut_d(buf_flush_validate());
+    os_thread_sleep(2000);
+    mutex_enter(&buf_pool->mutex);
+  }
 
-		os_thread_sleep(2000);
-		ut_d(buf_flush_validate());
-	}
+#ifdef UNIV_DEBUG
+  if (!first)
+  {
+    mutex_enter(&buf_pool->flush_list_mutex);
+
+    for (buf_page_t *bpage= UT_LIST_GET_FIRST(buf_pool->flush_list); bpage;
+         bpage= UT_LIST_GET_NEXT(list, bpage))
+    {
+      ut_ad(buf_page_in_file(bpage));
+      ut_ad(bpage->in_flush_list);
+      ut_ad(bpage->oldest_modification > 0);
+      ut_ad(id != bpage->id.space());
+    }
+
+    mutex_exit(&buf_pool->flush_list_mutex);
+  }
+#endif
 
-	ut_ad(first || buf_pool_get_dirty_pages_count(id) == 0);
+  mutex_exit(&buf_pool->mutex);
 }
 
 /** Empty the flush list for all pages belonging to a tablespace.

storage/innobase/include/buf0flu.h

@@ -221,11 +221,6 @@ buf_flush_ready_for_flush(
 	buf_flush_t	flush_type)/*!< in: type of flush */
 	MY_ATTRIBUTE((warn_unused_result));
 
-/** Determine the number of dirty pages in a tablespace.
-@param[in]	id		tablespace identifier
-@return number of dirty pages */
-ulint buf_pool_get_dirty_pages_count(ulint id);
-
 /** Synchronously flush dirty blocks.
 NOTE: The calling thread is not allowed to hold any buffer page latches! */
 void buf_flush_sync();