srinivasst commented on code in PR #9391: URL: https://github.com/apache/incubator-gluten/pull/9391#discussion_r2081154695
########## docs/developers/VeloxDynamicSizingOffheap.md: ########## @@ -0,0 +1,24 @@ +## Dynamic Off-heap Sizing +Spark requires setting both on-heap and off-heap memory sizes, which initializes different memory layouts. Improper configuration of these settings can lead to lower performance. Dynamic off-heap sizing is an experimental feature designed to simplify this process. When enabled, off-heap settings are ignored, and Velox uses the on-heap size as the memory size. +## Detail implementations +To understand the details, it's essential to learn the basics of JVM memory management. There are many resources discussing JVM internals: +- https://exia.dev/blog/2019-12-10/JVM-Memory-Model/ +- https://docs.oracle.com/cd/E13150_01/jrockit_jvm/jrockit/geninfo/diagnos/garbage_collect.html +- https://www.scaler.com/topics/memory-management-in-java/ +- https://developers.redhat.com/articles/2021/09/09/how-jvm-uses-and-allocates-memory# + +In general, the feature works as follows: + +- Spark first attempts to allocate memory based on the on-heap size. Note that the maximum memory size is controlled by spark.executor.memory. +- When Velox tries to allocate memory, Gluten attempts to allocate from system memory and records this in the memory allocator. +- If there is sufficient memory, allocations proceed normally. +- If memory is insufficient, Spark performs garbage collection (GC) to free on-heap memory, allowing Velox to allocate memory. Review Comment: In [gluten-core/src/main/java/org/apache/gluten/memory/memtarget/DynamicOffHeapSizingMemoryTarget.java](https://github.com/apache/incubator-gluten/blob/e9f65148a37bfc155b4b0c7bed60ce287cf0e37b/gluten-core/src/main/java/org/apache/gluten/memory/memtarget/DynamicOffHeapSizingMemoryTarget.java) the borrow code only checks for uncommitted memory (size + usedOffHeapMemory + totalHeapMemory <= TOTAL_MEMORY_SHARED). It does not acquire memory from the TaskMemoryManager How will this trigger spill / GC? -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
