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/*
* 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
import scala.collection.mutable
import org.apache.spark.Logging
/**
* Implements policies and bookkeeping for sharing a adjustable-sized pool of memory between tasks.
*
* Tries to ensure that each task gets a reasonable share of memory, instead of some task ramping up
* to a large amount first and then causing others to spill to disk repeatedly.
*
* If there are N tasks, it ensures that each task can acquire at least 1 / 2N of the memory
* before it has to spill, and at most 1 / N. Because N varies dynamically, we keep track of the
* set of active tasks and redo the calculations of 1 / 2N and 1 / N in waiting tasks whenever this
* set changes. This is all done by synchronizing access to mutable state and using wait() and
* notifyAll() to signal changes to callers. Prior to Spark 1.6, this arbitration of memory across
* tasks was performed by the ShuffleMemoryManager.
*
* @param lock a [[MemoryManager]] instance to synchronize on
* @param poolName a human-readable name for this pool, for use in log messages
*/
private[memory] class ExecutionMemoryPool(
lock: Object,
poolName: String
) extends MemoryPool(lock) with Logging {
/**
* Map from taskAttemptId -> memory consumption in bytes
*/
@GuardedBy("lock")
private val memoryForTask = new mutable.HashMap[Long, Long]()
override def memoryUsed: Long = lock.synchronized {
memoryForTask.values.sum
}
/**
* Returns the memory consumption, in bytes, for the given task.
*/
def getMemoryUsageForTask(taskAttemptId: Long): Long = lock.synchronized {
memoryForTask.getOrElse(taskAttemptId, 0L)
}
/**
* Try to acquire up to `numBytes` of memory for the given task and return the number of bytes
* obtained, or 0 if none can be allocated.
*
* This call may block until there is enough free memory in some situations, to make sure each
* task has a chance to ramp up to at least 1 / 2N of the total memory pool (where N is the # of
* active tasks) before it is forced to spill. This can happen if the number of tasks increase
* but an older task had a lot of memory already.
*
* @return the number of bytes granted to the task.
*/
def acquireMemory(numBytes: Long, taskAttemptId: Long): Long = lock.synchronized {
assert(numBytes > 0, s"invalid number of bytes requested: $numBytes")
// Add this task to the taskMemory map just so we can keep an accurate count of the number
// of active tasks, to let other tasks ramp down their memory in calls to `acquireMemory`
if (!memoryForTask.contains(taskAttemptId)) {
memoryForTask(taskAttemptId) = 0L
// This will later cause waiting tasks to wake up and check numTasks again
lock.notifyAll()
}
// Keep looping until we're either sure that we don't want to grant this request (because this
// task would have more than 1 / numActiveTasks of the memory) or we have enough free
// memory to give it (we always let each task get at least 1 / (2 * numActiveTasks)).
// TODO: simplify this to limit each task to its own slot
while (true) {
val numActiveTasks = memoryForTask.keys.size
val curMem = memoryForTask(taskAttemptId)
// How much we can grant this task; don't let it grow to more than 1 / numActiveTasks;
// don't let it be negative
val maxToGrant =
math.min(numBytes, math.max(0, (poolSize / numActiveTasks) - curMem))
// Only give it as much memory as is free, which might be none if it reached 1 / numTasks
val toGrant = math.min(maxToGrant, memoryFree)
if (curMem < poolSize / (2 * numActiveTasks)) {
// We want to let each task get at least 1 / (2 * numActiveTasks) before blocking;
// if we can't give it this much now, wait for other tasks to free up memory
// (this happens if older tasks allocated lots of memory before N grew)
if (memoryFree >= math.min(maxToGrant, poolSize / (2 * numActiveTasks) - curMem)) {
memoryForTask(taskAttemptId) += toGrant
return toGrant
} else {
logInfo(
s"TID $taskAttemptId waiting for at least 1/2N of $poolName pool to be free")
lock.wait()
}
} else {
memoryForTask(taskAttemptId) += toGrant
return toGrant
}
}
0L // Never reached
}
/**
* Release `numBytes` of memory acquired by the given task.
*/
def releaseMemory(numBytes: Long, taskAttemptId: Long): Unit = lock.synchronized {
val curMem = memoryForTask.getOrElse(taskAttemptId, 0L)
var memoryToFree = if (curMem < numBytes) {
logWarning(
s"Internal error: release called on $numBytes bytes but task only has $curMem bytes " +
s"of memory from the $poolName pool")
curMem
} else {
numBytes
}
if (memoryForTask.contains(taskAttemptId)) {
memoryForTask(taskAttemptId) -= memoryToFree
if (memoryForTask(taskAttemptId) <= 0) {
memoryForTask.remove(taskAttemptId)
}
}
lock.notifyAll() // Notify waiters in acquireMemory() that memory has been freed
}
/**
* Release all memory for the given task and mark it as inactive (e.g. when a task ends).
* @return the number of bytes freed.
*/
def releaseAllMemoryForTask(taskAttemptId: Long): Long = lock.synchronized {
val numBytesToFree = getMemoryUsageForTask(taskAttemptId)
releaseMemory(numBytesToFree, taskAttemptId)
numBytesToFree
}
}
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