srowen commented on a change in pull request #34846:
URL: https://github.com/apache/spark/pull/34846#discussion_r767166638
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File path: core/src/main/scala/org/apache/spark/memory/MemoryManager.scala
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@@ -255,7 +256,15 @@ private[spark] abstract class MemoryManager(
}
val size = ByteArrayMethods.nextPowerOf2(maxTungstenMemory / cores /
safetyFactor)
val default = math.min(maxPageSize, math.max(minPageSize, size))
- conf.get(BUFFER_PAGESIZE).getOrElse(default)
+ val sizeAsBytes = conf.get(BUFFER_PAGESIZE).getOrElse(default)
+ if (conf.get(MEMORY_ONHEAP_PAGESIZE_OPTIMIZE_ENABLED) &&
+ tungstenMemoryMode == MemoryMode.ON_HEAP &&
+ sizeAsBytes % (1024 * 1024) == 0 &&
+ Utils.isHumongousAllocation(sizeAsBytes)) {
+ sizeAsBytes - Platform.LONG_ARRAY_OFFSET
Review comment:
I suppose we lose a few bytes in the allocation, and maybe that makes
some nice power-of-two data structure not fit, but, I wonder if that's pretty
rare and if we can just go with this always indeed
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