WangGuangxin commented on a change in pull request #34846:
URL: https://github.com/apache/spark/pull/34846#discussion_r769443684
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File path: core/src/main/scala/org/apache/spark/memory/MemoryManager.scala
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@@ -255,7 +256,17 @@ 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 we are using G1 GC, it's better to take the LONG_ARRAY_OFFSET into
consideration
+ // so that the requested memory size is power of 2 and can be divided by
G1 region size
+ // to reduce memory waste within one G1 region
+ if (Utils.isG1GarbageCollector &&
Review comment:
I prefer not to put it in `HeapMemoryAllocator.allocate` because it may
break the semantics. When we do `HeapMemoryAllocator.allocate(size)` we
expected to get memory with specified size or throw oom, but we internally
change it to another value `(size-Platform.LONG_ARRAY_OFFSET)`, which may crash
the caller's code or brings confusion
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