I am trying to run a Java app which requires a large heap. It is running on AWS ECS inside a container. On a host with 128GB RAM. The container has ~115GB assigned.
The Dockerfile is based on eclipse-temurin:11
I am launching with the option -XX:MaxRAMPercentage=85.0 and also -XX:+PrintFlagsFinal to get feedback. This is what I get abridged (too large for SO) Full flags here https://pastebin.com/jm7Md2c8
2023-01-17 11:02:40 bool MaxFDLimit = true {product} {default}
2023-01-17 11:02:40 uintx MaxGCMinorPauseMillis = 18446744073709551615 {product} {default}
2023-01-17 11:02:40 uintx MaxGCPauseMillis = 200 {product} {default}
2023-01-17 11:02:40 uintx MaxHeapFreeRatio = 70 {manageable} {default}
2023-01-17 11:02:40 size_t MaxHeapSize = 32178700288 {product} {ergonomic}
2023-01-17 11:02:40 intx MaxInlineLevel = 15 {product} {default}
2023-01-17 11:02:40 intx MaxInlineSize = 35 {product} {default}
2023-01-17 11:02:40 size_t MaxMetaspaceExpansion = 5451776 {product} {default}
2023-01-17 11:02:40 uintx MaxMetaspaceFreeRatio = 70 {product} {default}
2023-01-17 11:02:40 size_t MaxMetaspaceSize = 18446744073709547520 {product} {default}
2023-01-17 11:02:40 size_t MaxNewSize = 19306381312 {product} {ergonomic}
2023-01-17 11:02:40 intx MaxNodeLimit = 80000 {C2 product} {default}
2023-01-17 11:02:40 uint64_t MaxRAM = 137438953472 {pd product} {default}
2023-01-17 11:02:40 uintx MaxRAMFraction = 4 {product} {default}
2023-01-17 11:02:40 double MaxRAMPercentage = 85.000000 {product} {command line}
2023-01-17 11:02:40 intx MaxRecursiveInlineLevel = 1 {product} {default}
2023-01-17 11:02:40 uintx MaxTenuringThreshold = 15 {product} {default}
2023-01-17 11:02:40 intx MaxTrivialSize = 6 {product} {default}
2023-01-17 11:02:40 intx MaxVectorSize = 32 {C2 product} {default}
2023-01-17 11:02:40 size_t MetaspaceSize = 21807104 {pd product} {default}
2023-01-17 11:02:40 bool MethodFlushing = true {product} {default}
2023-01-17 11:02:40 size_t MinHeapDeltaBytes = 4194304 {product} {ergonomic}
2023-01-17 11:02:40 uintx MinHeapFreeRatio = 40 {manageable} {default}
2023-01-17 11:02:40 intx MinInliningThreshold = 250 {product} {default}
2023-01-17 11:02:40 intx MinJumpTableSize = 10 {C2 pd product} {default}
2023-01-17 11:02:40 size_t MinMetaspaceExpansion = 339968 {product} {default}
2023-01-17 11:02:40 uintx MinMetaspaceFreeRatio = 40 {product} {default}
2023-01-17 11:02:40 uintx MinRAMFraction = 2 {product} {default}
2023-01-17 11:02:40 double MinRAMPercentage = 50.000000 {product} {default}
2023-01-17 11:02:40 uintx MinSurvivorRatio = 3 {product} {default}
2023-01-17 11:02:40 bool UseContainerSupport = true {product} {default}
So it seems reasonable, the JVM detected the host ram MaxRAM = 137438953472 = 128GB the option MaxRAMPercentage = 85.000000 was correctly set. UseContainerSupport = true so my understanding is these options should be applied.
So I dont understand why MaxHeapSize = 32178700288 which is only ~29.9GB? I think its 1/4 of the 115GB assigned to the container which seems to imply my settings are not being applied, why?.
Testing locally with
docker run --memory='2g' eclipse-temurin:11 java -XX:MaxRAMPercentage=85.0 -XX:+PrintFlagsFinal -version | grep MaxHeapSize
Appears to work as expected when varying the container memory assigned and the MaxRAMPercentage
Thanks to Andrey. The solution was to add -XX:-UseCompressedOops