Question about memory usage

[Michał Kondraciuk]

Hello,

Originally I wanted to report this to bug-gnu-emacs, but it's so basic 
that I thought I'd ask here instead.

Basically, when I run the sexp below in emacs -Q, Emacs keeps allocating 
a lot of memory. In 10 minutes, it goes from 18 MB to over 200 MB.

(while t
  (with-temp-buffer
    (setq buffer-undo-list nil)
    (insert "a")))


Calling garbage-collect afterwards or even inside the body of the loop 
doesn't help (except the loop obviously runs slower, so after 10 
minutes, Emacs uses ~100 MB of memory).
So I want to know if this behavior is expected for some reason? Does 
Emacs reuse this memory somehow (to make future allocations faster)? I 
tested on newest master and 25.3 and the behavior is the same.