[systemd-devel] Looking for known memory leaks triggered by stress testing add/remove/up/down interfaces

[Lennart Poettering]

On Do, 18.02.21 11:48, Robert P. J. Day (rpjday at crashcourse.ca) wrote:

>   A colleague has reported the following apparent issue in a fairly
> old (v230) version of systemd -- this is in a Yocto Project Wind River
> Linux 9 build, hence the age of the package.
>
>   As reported to me (and I'm gathering more info), the system was
> being put through some "longevity testing" by repeatedly adding,
> removing, activating and de-activating network interfaces. According
> to the report, the result was heap space slowly but inexorably being
> consumed.
>
>   While waiting for more info, I'm going to examine the commit log for
> systemd from v230 moving forward to collect any commits that address
> memory leaks, then peruse them more carefully to see if they might
> resolve the problem.
>
>   I realize it's asking a bit for folks here to remember that far
> back, but does this issue sound at all familiar? Any pointers that
> might save me some time? Thanks.

Note that our hash tables operate with an allocation cache: when
adding entries to them and then removing them again the memory
required for that is not returned to the OS but added to a local
cache. When the next entry is then added again, we recycle the cached
entry instead of asking for new memory again. This allocation cache is
a bit quicker then going to malloc() all the time, but means if you
just watch the heap you'll assume there's a leak even though there
isn't really, the memory is not lost after all, and will be reused
eventually if we need it.

You may use the env var SYSTEMD_MEMPOOL=0 to turn this logic off, but
not sure v230 already knew that env var.

Lennart

--
Lennart Poettering, Berlin