WangGuangxin opened a new pull request #34846:
URL: https://github.com/apache/spark/pull/34846
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### What changes were proposed in this pull request?
As we may know, a phenomenon called `humongous allocations` exists in G1GC
when allocations that are larger than 50% of the region size.
Spark's tungsten memory model usually tries to allocate memory by one `page`
each time and allocated by `long[pageSizeBytes/8]` in
`HeapMemoryAllocator.allocate`.
Remember that java long array needs extra object header (usually 16 bytes in
64bit system), so the really bytes allocated is `pageSize+16`.
Assume that the `G1HeapRegionSize` is 4M and `pageSizeBytes` is 4M as well.
Since every time we need to allocate 4M+16byte memory, so two regions are used
with one region only occupies 16byte. Then there are about **50%** memory waste.
It can happenes under different combinations of G1HeapRegionSize (varies
from 1M to 32M) and pageSizeBytes (varies from 1M to 64M).
This PR try to optimize the pageSize to avoid memory waste.
This case exists not only in `MemoryManagement`, but also in other places
such as `TorrentBroadcast.blockSize`. I would like to submit a followup PR if
this modification is reasonable.
### Why are the changes needed?
To avoid memory waste in G1 GC
### Does this PR introduce _any_ user-facing change?
No
### How was this patch tested?
Existing UT
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