Github user tedyu commented on a diff in the pull request:
https://github.com/apache/spark/pull/9344#discussion_r44212316
--- Diff: core/src/main/scala/org/apache/spark/memory/MemoryPool.scala ---
@@ -0,0 +1,71 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.memory
+
+import javax.annotation.concurrent.GuardedBy
+
+/**
+ * Manages bookkeeping for an adjustable-sized region of memory. This
class is internal to
+ * the [[MemoryManager]]. See subclasses for more details.
+ *
+ * @param lock a [[MemoryManager]] instance, used for synchronization. We
purposely erase the type
+ * to `Object` to avoid programming errors, since this object
should only be used for
+ * synchronization purposes.
+ */
+abstract class MemoryPool(lock: Object) {
+
+ @GuardedBy("lock")
+ private[this] var _poolSize: Long = 0
+
+ /**
+ * Returns the current size of the pool, in bytes.
+ */
+ final def poolSize: Long = lock.synchronized {
+ _poolSize
+ }
+
+ /**
+ * Returns the amount of free memory in the pool, in bytes.
+ */
+ final def memoryFree: Long = lock.synchronized {
+ _poolSize - memoryUsed
+ }
+
+ /**
+ * Expands the pool by `delta` bytes.
+ */
+ final def incrementPoolSize(delta: Long): Unit = lock.synchronized {
+ require(delta >= 0)
+ _poolSize += delta
+ }
+
+ /**
+ * Shrinks the pool by `delta` bytes.
+ */
+ final def decrementPoolSize(delta: Long): Unit = lock.synchronized {
+ require(delta >= 0)
+ require(delta <= _poolSize)
+ require(_poolSize - delta >= memoryUsed)
--- End diff --
Can this check be modified such that at most _poolSize - memoryUsed bytes
are freed and the actual number of bytes freed is returned ?
This way shrinkPoolToFreeSpace() can check this return value and do
eviction accordingly.
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