Hi Nicholas, I have a smoker that runs the cpan shell for about 10 days in a single process. Its duty is simply to smoke all distros currently on the CPAN in a random order. I have gathered experiences with this smoker for about three years: up until v5.35.5 I never observed that it ran out of memory. Now, with v5.35.5 it did run out of memory. This is reproducable. To provide an estimate of the scale of the impact: the VM that runs the smoker is equipped with 12G memory plus 0.5G swap; for a smoke run with v5.35.4 munin showed that it had reached an amount of memory committed of 6G after having run for ten days; with v5.35.5 the smoker was killed with OOM after about three days; that means in a third of the time we consumed twice as much memory, so I estimate the scale impact to be sixfold. Bisect to the rescue: 94ee6ed79dbca73d0345b745534477e4017fb990 is the first bad commit commit 94ee6ed79dbca73d0345b745534477e4017fb990 Author: Nicholas Clark <nick@ccl4.org> Date: Fri Aug 20 15:20:13 2021 +0000 Split the XPVHV body into two variants "normal" and "with aux" Default to the smaller body, and switch to the larger body if we need to allocate a C<struct xpvhv_aux> (eg need an iterator). This restores the previous small size optimisation for hashes used as objects. :100644 100644 ff3729fa5f176adffacb7d2088707fab601782a7 749ede6f5b5d2998a17d18bdabdadc5fb96fa638 M embed.fnc :100644 100644 954eb493d651ab12dcafcf6d6df670b2ba19bcbd 7e8f286859f3cb04dbe2300c1a63d69cba7f56c6 M hv.c :100644 100644 285a004a5f4c6be21370557ff03ac0fd0da5e9b2 c7aeb7de572631a42181ee2056ce6f815114129f M hv.h :100644 100644 0fe96719b0252434423253fc432da2b5b1da1acc 7b65b1390cfe3742f05c2529b8b574e3aa5a39d2 M proto.h :100644 100644 5dfe3d9c8911ff949aa7c75e301dab1910476dc6 989017d5abfb887b38eca28dd72f447ae4919b86 M sv.c :100644 100644 83fa92380b757a38d068e014626f107994c1784c c4ee1529890d5217cbfd916f17fac8d22a8e4d43 M sv.h Let me know which other infos I should provide to give you a better picture of the situation. Greetings from Berlin, -- andreasThread Next