When an archive region is deallocated (e.g. if we did not manage to map in or find an archive), the G1CollectedHeap::dealloc_archive_regions() method shrinks the heap (i.e. uncommits the region) unconditionally.

This is wrong in case this would decrease the allocated heap below -Xms.

Particularly noticeable with -Xms == -Xmx and running with gc+region=trace debugging: at the beginning G1 allocates a region as closed archive, but then *uncommits* it.

This may cause really minor performance hiccups/regressions, but often G1 re-commits that region later anyway.

Afaict this is a bug introduced with the initial archive regions support.