Feature Request: Support for Jemalloc w/o Separate Build Pack

[ksylvest]

Does the team maintaining this buildpack have any interest in a PR to install jemalloc by default / set a LD_PRELOAD env variable w/ this buildpack? It seems like a more sensible default to include (especially since the latest versions of Rails are shipping w/ it installed via Docker):

https://github.com/rails/rails/pull/50943/files

[schneems]

The reason given is to reduce memory fragmentation. We're mitigating that in glibc via setting this environment variable by default https://github.com/heroku/heroku-buildpack-ruby/blob/633a1d170155c279e4a5803fc8352d93108ec1b9/changelogs/v205/malloc.md?plain=1.

I'm possibly interested in exploring doing something with jemalloc, but I think there are more caveats than that PR you linked to would lead you to believe. (Or at least I remember there being some caveats last time I looked into it).

I wouldn't do it here. I would do it on https://github.com/heroku/buildpacks-ruby which is the future. The path forward would look like: Making our own jemalloc buildpack, and then optionally requiring it to run before heroku/ruby based on some detection logic and making it disable-able as well.

[swrobel]

@schneems is there some sort of migration guide from traditional buildpacks like this one to CNB, assuming it's recommended to run them in prod on Heroku at this point?