8343153: compiler/codecache/CheckLargePages.java fails on linux with huge pages configured but its number set to 0

[dafedafe]

Issue

The third test of compiler/codecache/CheckLargePages.java checks that non-segmented 1GB code cache can be allocated with 1GB large pages.

On linux (the only supported platform) in order to allocate them, 1GB huge pages have to be enabled (checkable from /proc/meminfo and /sys/kernel/mm/hugepages/hugepages-xxxx) and their number has to be set to >0 (checkable from /sys/kernel/mm/hugepages/hugepages-xxxx/nr_hugepages).

If 1GB huge pages are enabled but their number is 0, the test fails because it looks for a string that matches CodeCache: min=1[gG] max=1[gG] base=[^ ]+ size=1[gG] page_size=1[gG] but the actual output is CodeCache: min=1G max=1G base=0x00007f4040000000 size=1G page_size=2M. This happens because the VM tries to allocate 1GB huge pages but it fails beause the number of allocatable ones is 0 and the VM reverts to smaller page sizes (2MB in this case).

Solution

The problem might be attributed to the VM only checking for 1GB huge pages to be supported, not how many there currently are. Nevertheless, this seems to be the correct behaviour, not least because their number can be changed dynamically.
So, the correct thing to do seems to be to "relax" the check made by the test to include both cases:

• when 1GB huge pages are supported and can be allocated correctly
• when 1GB huge pages are supported and cannot be allocated correctly (because there are none available)

---

Progress

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Issue

• JDK-8343153: compiler/codecache/CheckLargePages.java fails on linux with huge pages configured but its number set to 0 (Bug - P4)

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