RFR: 8318817: Could not reserve enough space in CodeHeap 'profiled nmethods' (0K)

[Roberto Castañeda Lozano]

On Thu, 26 Oct 2023 09:33:16 GMT, Daniel Lundén <duke at openjdk.org> wrote:

> This changeset fixes an issue where certain large values of `-XX:NMethodSizeLimit` could cause code heap initialization to fail with the error message
> 
> Error occurred during initialization of VM
> Could not reserve enough space in CodeHeap 'profiled nmethods' (0K)
> 
> 
> Two components in `CodeCache::initialize_heaps` may cause the error:
> 1. The minimum size (`min_size = os::vm_page_size();`) for profiled and non-profiled code heaps is sometimes not large enough. Specifically, when `profiled_size` and/or `non_profiled_size` are set to `min_size` and `alignment > os::vm_page_size()`, the `align_down` below (from `CodeCache::initialize_heaps`) sets the size to 0.
>       ```
>       const size_t alignment = MAX2(ps, os::vm_allocation_granularity());
>       non_nmethod_size = align_up(non_nmethod_size, alignment);
>       profiled_size    = align_down(profiled_size, alignment);
>       non_profiled_size = align_down(non_profiled_size, alignment);
>       ```
> 2. The calculation for default code heap sizes does not consider the edge case when `cache_size > non_nmethod_size > cache_size - 2 * min_size`.
> 
> This changeset
> 1. ensures that `min_size >= alignment`, and
> 2. fixes the edge case.
> 
> The changeset includes new tests that exercise the above, also in combination with `-XX:+UseLargePages -XX:+UseTransparentHugePages` on Linux  to test the case when `os::can_execute_large_page_memory()` is true (which can affect `alignment`).
> 
> ### Testing (on all Oracle-supported platforms)
> `tier1`, `tier2`, `tier3`, `tier4`, `tier5`

src/hotspot/share/code/codeCache.cpp line 206:

> 204:   size_t min_size           = MAX3(os::vm_page_size(),
> 205:                                    os::vm_allocation_granularity(),
> 206:                                    ps);

Is there a VM configuration in which `ps` could be smaller than `os::vm_page_size()`? If not, we could simplify this expression to `MAX2(os::vm_allocation_granularity(), ps)`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16373#discussion_r1376355237