I don't think it's actually any change in ceval per se, or any new buffers, just how the compiler code generation has changed due to this commit.

Based on some local testing, the triggering issue is the exclusion of the optimization pragma entirely in debug mode.  It appears that the existing code required the pragma to be enabled to stay within the available stack space.

A quick reproduction is running test_pickletools.  It fails abruptly and quickly, at least on the worker, without the pragma, but runs to completion if enabled.

Perhaps that aspect of the commit should be reverted, maybe with a separate flag for debugging ceval (but not normal testing)?  Alternatively, is there a way to increase the stack in debug mode to compensate?  Though I guess that would risk missing a release-build only stack issue.