JDK-8261401 : Add sanity check for UseSHM large pages similar to the one used with hugetlb large pages
- Type: Enhancement
- Component: hotspot
- Sub-Component: gc
- Affected Version: 17
- Priority: P4
- Status: Resolved
- Resolution: Fixed
- Submitted: 2021-02-09
- Updated: 2021-03-02
- Resolved: 2021-02-17
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| JDK 17 |
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17 b11Fixed  |
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Description
When large pages are enabled on Linux (using -XX:+UseLargePages), both UseHugeTLBFS and UseSHM can be used. We prefer to use HugeTLBFS and first do a sanity check to see if this kind of large pages are available and if so we disable UseSHM. The problematic part is when HugeTLBFS pages are not available, then we disable this flag and without doing any sanity check for UseSHM, we mark large pages as enabled using SHM. The thing with SHM is that it requires the same type of explicitly allocated huge pages as HugeTLBFS and also privileges to lock memory. So it is likely that in the case of not being able to use HugeTLBFS we probably can't use SHM either. A fix for this would be to do a similar sanity check as currently done for HugeTLBFS and if it fails disable UseLargePages since we will always fail such allocation attempts anyways.
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