Use top-down direction for heap allocation on zLinux #7344
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Object heap allocation logic for zLinux running with Concurrent Scavenger with HW support (Guarded Storage) has not been changed by this PR and still use bottom-up direction. |
dmitripivkine
commented
May 23, 2024
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@amicic Would you please review? |
amicic
reviewed
May 23, 2024
amicic
reviewed
May 23, 2024
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looks good to me |
amicic
reviewed
May 23, 2024
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Correspondent issue: eclipse-openj9/openj9#19490 |
amicic
approved these changes
May 23, 2024
Current heap allocation direction for zLinux is bottom-up. The motivation for this is on Z platforms shift operation executes faster for smaller shift value. However with bottom-up direction object heap takes all available memory below 4G bar. This does not allow Suballocator to expand if necessary and might lead to OOM below 4G bar. The intention for this fix is to improve this situation. Switching to top-down increases chances that less memory below 4G bar is going to be used (but worst case scenario still be the same as now). In order to keep smaller shift performance benefit an allocation shift scheme should stay 0-1-2-3-4. All other platforms still use 0-3-4. Heap allocation logic for Concurrent Scavenger with HW support (Guarded Storage) hasn't been changed and still be bottom-up. The behaviour for all other platforms hasn't been changed. Signed-off-by: Dmitri Pivkine <Dmitri_Pivkine@ca.ibm.com>
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jenkins build all |
babsingh
approved these changes
May 24, 2024
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Current heap allocation direction for zLinux is bottom-up. The motivation for this is on Z platforms shift operation executes faster for smaller shift value. However with bottom-up direction object heap takes all available memory below 4G bar. This does not allow Suballocator to expand if necessary and might lead to OOM below 4G bar. The intention for this fix is to improve this situation. Switching to top-down increases chances that less memory below 4G bar is going to be used (but worst case scenario still be the same as now). In order to keep smaller shift performance benefit an allocation shift scheme should stay 0-1-2-3-4. All other platforms still use 0-3-4. The behaviour for all other platforms has not been changed.