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[SPARK-23516][CORE] It is unnecessary to transfer unroll memory to storage memory #20676

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[SPARK-23516][CORE] It is unnecessary to transfer unroll memory to storage memory #20676

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21 changes: 12 additions & 9 deletions core/src/main/scala/org/apache/spark/storage/memory/MemoryStore.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -246,18 +246,18 @@ private[spark] class MemoryStore(
val amountToRequest = size - unrollMemoryUsedByThisBlock
keepUnrolling = reserveUnrollMemoryForThisTask(blockId, amountToRequest, memoryMode)
if (keepUnrolling) {
unrollMemoryUsedByThisBlock += amountToRequest
unrollMemoryUsedByThisBlock = size
}
} else if (size < unrollMemoryUsedByThisBlock) {
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@Ngone51 Ngone51 Feb 27, 2018

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#19285 miss this check before? Oops! This could waste storage memory. Thanks for adding this.
Also, cc @cloud-fan @ConeyLiu

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@ConeyLiu ConeyLiu Feb 28, 2018

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In #19285, we first release unrollMemoryUsedByThisBlock unroll memory, and then we request entry.size storage memory. So, there is no waste of resources here.

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@10110346 10110346 Feb 28, 2018

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There is no problem before,because it releases all unroll memory in 257 line

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@Ngone51 Ngone51 Feb 28, 2018

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Ah, I see, glad to hear that.

releaseUnrollMemoryForThisTask(memoryMode, unrollMemoryUsedByThisBlock - size)
unrollMemoryUsedByThisBlock = size
}

if (keepUnrolling) {
val entry = entryBuilder.build()
// Synchronize so that transfer is atomic
memoryManager.synchronized {
releaseUnrollMemoryForThisTask(memoryMode, unrollMemoryUsedByThisBlock)
val success = memoryManager.acquireStorageMemory(blockId, entry.size, memoryMode)
assert(success, "transferring unroll memory to storage memory failed")
}
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@Ngone51 Ngone51 Feb 27, 2018

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It's a concept difference between unroll memory and storage memory. And it seems reasonable to transfer unroll memory to storage memory from the view of their concept, though, it makes no big difference underlying storage memory. I'm not sure will this change cause some side effect, if none, I'll approve of it.

// In fact, unroll memory is also storage memory, it is unnecessary to
// release unroll memory really
releaseUnrollMemoryForThisTask(memoryMode, unrollMemoryUsedByThisBlock, false)
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@Ngone51 Ngone51 Feb 27, 2018

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Did you check other calls on this function? Are you sure all other calls' third param default to be true, except here only?

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@10110346 10110346 Feb 28, 2018 •
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I am sure all other calls' third param default to be true

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@Ngone51 Ngone51 Feb 28, 2018

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Well, it seems a little awkward. How about change transferUnrollToStorage()'s(which is removed after #19285, see L242 ) behavior , rather than releaseUnrollMemoryForThisTask ?


entries.synchronized {
entries.put(blockId, entry)
Expand Down Expand Up @@ -565,7 +565,8 @@ private[spark] class MemoryStore(
* Release memory used by this task for unrolling blocks.
* If the amount is not specified, remove the current task's allocation altogether.
*/
def releaseUnrollMemoryForThisTask(memoryMode: MemoryMode, memory: Long = Long.MaxValue): Unit = {
def releaseUnrollMemoryForThisTask(memoryMode: MemoryMode, memory: Long = Long.MaxValue,
releaseMemoryReally: Boolean = true): Unit = {
val taskAttemptId = currentTaskAttemptId()
memoryManager.synchronized {
val unrollMemoryMap = memoryMode match {
Expand All @@ -576,7 +577,9 @@ private[spark] class MemoryStore(
val memoryToRelease = math.min(memory, unrollMemoryMap(taskAttemptId))
if (memoryToRelease > 0) {
unrollMemoryMap(taskAttemptId) -= memoryToRelease
memoryManager.releaseUnrollMemory(memoryToRelease, memoryMode)
if (releaseMemoryReally) {
memoryManager.releaseUnrollMemory(memoryToRelease, memoryMode)
}
}
if (unrollMemoryMap(taskAttemptId) == 0) {
unrollMemoryMap.remove(taskAttemptId)
Expand Down