Github user JoshRosen commented on a diff in the pull request:
https://github.com/apache/spark/pull/18296#discussion_r122344684
--- Diff:
core/src/main/scala/org/apache/spark/memory/UnifiedMemoryManager.scala ---
@@ -171,7 +171,8 @@ private[spark] class UnifiedMemoryManager
private[memory] (
if (numBytes > storagePool.memoryFree) {
// There is not enough free memory in the storage pool, so try to
borrow free memory from
// the execution pool.
- val memoryBorrowedFromExecution = Math.min(executionPool.memoryFree,
numBytes)
+ val memoryBorrowedFromExecution = Math.min(executionPool.memoryFree,
+ numBytes - storagePool.memoryFree)
--- End diff --
This change makes sense: if we hit this branch then we've failed to acquire
enough memory to store a block. In particular, we might need `M` bytes of
memory but only `A` are available in storage. In this case, we should only
request the `(M - A)` bytes of extra memory that we need, but the old code was
incorrectly requesting all `M` which would cause us to over-evict. Therefore, I
think this change is correct.
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