On Fri, 26 Apr 2024 21:16:03 GMT, Vladimir Kozlov <k...@openjdk.org> wrote:
> Move immutable nmethod's data from CodeCache to C heap. It includes > `dependencies, nul_chk_table, handler_table, scopes_pcs, scopes_data, > speculations, jvmci_data`. It amounts for about 30% (optimized VM) of space > in CodeCache. > > Use HotSpot's `os::malloc()` to allocate memory in C heap for immutable > nmethod's data. Bail out compilation if allocation failed. > > Shuffle fields order and change some fields size from 4 to 2 bytes to avoid > nmethod's header size increase. > > Tested tier1-5, stress,xcomp > > Our performance testing does not show difference. > > Example of updated `-XX:+PrintNMethodStatistics` output is in JBS comment. It only makes sense if the immutable data heap is not also used for other critical resources. If malloc or metaspace were used as the immutable data heap, normally failures in those heaps are fatal, because other critical resources (monitors, classes, etc) are allocated from there, so any failure means the JVM is about to die. There's no reason to find a fall-back method to allocate a new nmethod in that case. ------------- PR Comment: https://git.openjdk.org/jdk/pull/18984#issuecomment-2081364009
