RAM Class: Per-kind segment allocation and sizing #22530
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fyi @tajila |
tajila
reviewed
Sep 3, 2025
runtime/vm/createramclass.cpp
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| /* static slots fragment */ | ||
| allocationRequests[RAM_STATICS_FRAGMENT].prefixSize = 0; | ||
| allocationRequests[RAM_STATICS_FRAGMENT].alignment = sizeof(U_64); | ||
| allocationRequests[RAM_STATICS_FRAGMENT].alignedSize = totalStaticSlots * sizeof(UDATA); | ||
| allocationRequests[RAM_STATICS_FRAGMENT].address = NULL; | ||
| allocationRequests[RAM_STATICS_FRAGMENT].segmentKind = INFREQUENTLY_ACCESSED; |
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Updated. Now, only RAM_STATICS_FRAGMENT is tagged as FREQUENTLY_ACCESSED, and the rest are tagged as INFREQUENTLY_ACCESSED.
babsingh
commented
Sep 3, 2025
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| const UDATA headersPerSegment = 32; | ||
| classAllocationIncrement = sizeof(J9Class) * headersPerSegment; |
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Should alignment be considered here?
Suggested change
| const UDATA headersPerSegment = 32; | |
| classAllocationIncrement = sizeof(J9Class) * headersPerSegment; | |
| UDATA mask = J9_REQUIRED_CLASS_ALIGNMENT - 1; | |
| UDATA unitSegment = (sizeof(J9Class) + mask) & ~mask; | |
| const UDATA headersPerSegment = 32; | |
| classAllocationIncrement = unitSegment * headersPerSegment; |
Introduce distinct segment categories (SUB4G, FREQUENTLY_ACCESSED, INFREQUENTLY_ACCESSED). Separates hot vs. cold J9Class data for better memory efficiency. SUB4G segments are sized in multiples of aligned J9Class headers and tagged with MEMORY_TYPE_RAM_CLASS_SUB4G. Related: eclipse-openj9#20644 Co-authored-by: Nick Kamal <nick.kamal@ibm.com> Signed-off-by: Babneet Singh <sbabneet@ca.ibm.com>
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Introduce distinct segment categories (
SUB4G,FREQUENTLY_ACCESSED,INFREQUENTLY_ACCESSED).Separates hot vs. cold
J9Classdata for better memory efficiency.SUB4Gsegments are sized in multiples of alignedJ9Classheadersand tagged with
MEMORY_TYPE_RAM_CLASS_SUB4G.Related: #20644
Depends on eclipse-omr/omr#7916