Issue #21856 has been updated by byroot (Jean Boussier). Subject changed from Nokogiri performance degradation since Ruby 4.0 to Massive performance degradation of `rb_obj_free` for `T_CLASS` since Ruby 4.0 I spent some time trying to fix this, I think it's possible but is a pretty major refactoring. In 3.4: Classes have a `subclasses` doubly-linked list, which is necessary to be able to iterate subclasses efficiently. As to be able to purge these list effectively, each class also keep a direct reference to the node than contain themselves in the parent linked list (`subclass_entry`). They also have another linked list with all the module its been included on. All this allows to efficiently remove all the references to a given class. In 4.0: It's roughly the same, except the 3 references above are all behind an extra st_table indirection. So before you can access any of these lists, you need to do an extra hash lookup. To be very honest I don't understand why it is necessary, given these lists are inside `rb_classext_t` and from my understanding classes have one `rb_classext_t` per box, so that indirection seem redundant to me. But then again, I don't understand the box design well, so I may be overlooking something, and I don't know if that's something I can reasonably fix. cc @tagomoris @ko1 ---------------------------------------- Bug #21856: Massive performance degradation of `rb_obj_free` for `T_CLASS` since Ruby 4.0 https://bugs.ruby-lang.org/issues/21856#change-116257 * Author: ahorek (Pavel Rosický) * Status: Open * ruby -v: ruby 4.1.0dev (2026-01-31T09:41:30Z master 7ef8c470d2) +PRISM [x86_64-linux] * Backport: 3.2: DONTNEED, 3.3: DONTNEED, 3.4: DONTNEED, 4.0: REQUIRED ---------------------------------------- Loofah sanitization is noticeably slower ``` Ruby: 3.4.8 Loofah: 2.25.0 Nokogiri: 1.19.0 Iterations: 100000 user system total real Loofah.fragment + scrub!(:prune) 26.091872 0.000000 26.091872 ( 25.110925) Loofah.scrub_fragment(:prune) 25.913185 0.010392 25.923577 ( 24.948464) Nokogiri HTML parse only 3.852690 0.000000 3.852690 ( 3.705930) Ruby: 4.0.0 & 4.0.1 Loofah: 2.25.0 Nokogiri: 1.19.0 Iterations: 100000 user system total real Loofah.fragment + scrub!(:prune) 38.094207 0.041753 38.135960 ( 36.669463) Loofah.scrub_fragment(:prune) 40.168795 0.000045 40.168840 ( 38.561806) Nokogiri HTML parse only 4.012936 0.052024 4.064960 ( 3.913272) Ruby: 4.1.0 (ruby 4.1.0dev (2026-01-31T09:41:30Z master 7ef8c470d2) +PRISM [x86_64-linux]) Loofah: 2.25.0 Nokogiri: 1.19.0 Iterations: 100000 user system total real Loofah.fragment + scrub!(:prune) 39.004228 0.000000 39.004228 ( 37.694873) Loofah.scrub_fragment(:prune) 39.043199 0.031284 39.074483 ( 37.182785) Nokogiri HTML parse only 3.889100 0.010427 3.899527 ( 3.741622) ``` Originally reported https://www.redmine.org/issues/43737 ---Files-------------------------------- benchmark.rb (1002 Bytes) -- https://bugs.ruby-lang.org/