On Fri, 8 May 2026 17:19:59 GMT, Vladimir Kozlov <[email protected]> wrote:
>> src/hotspot/share/ci/ciEnv.cpp line 1124:
>>
>>> 1122: // No safepoints are allowed. Otherwise, class redefinition can
>>> occur in between.
>>> 1123: MutexLocker ml(Compile_lock);
>>> 1124: NoSafepointVerifier nsv;
>>
>> OK, so here is an interesting lifecycle oddity. We are here arming `NSV` for
>> class redefinition reasons. Looks fine until we go to
>> `ciEnv::make_code_usable`, which builds `MCS` for preloaded methods. But
>> `MCS` allocation is _Metaspace_ allocation, so it can trigger GC allocation
>> failure and GC safepoint. So this `NSV` may fail.
>
> In CompileBroker we generate MC unconditionally before creating compilation
> task:
>
> // Tiered policy requires MethodCounters to exist before adding a method to
> // the queue. Create if we don't have them yet.
> method->get_method_counters(thread);
>
>
> Also in `ciEnv::is_compilation_valid()` we have:
>
> // We require method counters to store some method state (max compilation
> levels) required by the compilation policy.
> if (method->get_method_counters(thread) == nullptr) {
> record_failure("can't create method counters");
> return false;
> }
>
>
> May be we should do the same check in CompileBroker.
I added check to CompileBroker code. And I moved `get_method_counters` from
`ciEnv::is_compilation_valid()` to callers before `NoSafepointVerifier nsv;`.
>> src/hotspot/share/code/aotCodeCache.cpp line 737:
>>
>>> 735:
>>> 736: size_t codeCacheSize = pointer_delta(CodeCache::high_bound(),
>>> CodeCache::low_bound(), 1);
>>> 737: if (codeCacheSize > _codeCacheSize) { // Only allow smaller or equal
>>> CodeCache size in production run
>>
>> It is not very clear to me why do we have this limit. What breaks if we have
>> a larger code cache in production run? Some branches become not easily
>> reachable, or something else? Let's polish the error message too: we need to
>> say "larger" or "smaller" explicitly, so users can figure out what to adjust.
>
> We will not be able to patch some branch/call instructions in AOT code if
> CodeCache become bigger in production.
> Remember that we have short branches and far branches. So distance to stubs,
> for example, could change with bigger CodeCache and it would not fit into
> short branch encoding.
New message: `it was created with smaller CodeCache size = %dKb vs current %dKb`
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/30778#discussion_r3210323187
PR Review Comment: https://git.openjdk.org/jdk/pull/30778#discussion_r3210170451
