A year and a half ago (already), I landed replace-malloc, a feature that allows more memory allocator flexibility in Firefox. It enabled building tools such as the dark matter detector (aka DMD) more easily. It also allows to replace our default allocator, (moz)jemalloc.
Until now, you had to explicitly enable the feature with –enable-replace-malloc. As of writing, it is enabled by default on all builds except Windows builds with jemalloc disabled (but that’s due to change too). Note Windows debug builds, as well as local Windows builds have jemalloc disabled by default.
It currently is only on mozilla-inbound, but should propagate quickly to other branches. It won’t, however, ride the trains: it will stay disabled on aurora, beta, release, esr.
Relatedly, two years ago (already), I landed jemalloc 3.0.0, and updated it until 3.2.0 six months later. It was and still is disabled by default. Sadly, it hasn’t seen an update since then. The recent increase in activity around improving the memory footprint of our own fork of jemalloc (dating back to before version 1.0) made me want to update it at last.
This is now done, and the tree contains a (slightly patched) copy of jemalloc 3.6.0. And combined with replace-malloc, it is now possible to test it on nightly builds (well, starting from the one after the next mozilla-inbound merge to mozilla-central) with the following:
- On GNU/Linux:
$ LD_PRELOAD=/path/to/libreplace_jemalloc.so firefox
- On OSX:
$ DYLD_INSERT_LIBRARIES=/path/to/libreplace_jemalloc.dylib firefox
- On Windows:
$ MOZ_REPLACE_MALLOC_LIB=drive:\path\to\replace_jemalloc.dll firefox
No, you don’t need to rebuild Firefox to test it with jemalloc 3.6.0. The relevant library is now shipped in the nightly builds. Except on Android, as I haven’t figured where to put it, but you can take the
.so file from a local build and use it with a nightly build.
I would appreciate if several people could start using jemalloc 3.x this way. There is still work to do to make it the default. In fact, the list of dependencies of the tracking bug still has the same bugs I filed a long time ago. Hopefully, the ease of use will make someone want to scratch those itches. Please ping me if you want to take one of those bugs.