Firefox 7 is currently in the Aurora channel. Its memory usage improvements have been getting a lot of attention this week, with many people reporting the 30% improvement claims from the official blog post. I was worried about the post claiming a specific percentage improvement, because there are various ways to measure memory usage, and it varies so greatly depending on the workload, but I haven’t seen anybody dispute it so far. In fact, the only non-Mozilla measurement I saw was one where a reviewer opened 117 bookmarks at once (one bookmark per tab) and saw a 40% reduction in private bytes on Windows! This was a pleasant surprise as we were expecting improvements mostly when users (a) closed lots of tabs, or (b) left the browser idle for a long time.
The most significant MemShrink-related landings this week were things that were subsequently backed out. Paul Biggar landed jemalloc support for Mac, then had to revert it due to some crashes and possible memory usage regressions. This support has ended up being an enormous hassle, and Paul’s been tirelessly battling various Mac OS X quirks and annoyances over a period of several months. An earlier appraisal that “It should be pretty trivial… I don’t think any of this would be a ton of work. Maybe a week of trying a few different things and running it through our unit tests?” turned out to be spectacularly wrong. Hopefully Paul will be able to fix the problems and re-land soon.
On the tools front:
- Per-compartment memory reporters have found several cases of “zombie compartments”, which is when a tab is closed but one or more of its compartments stay around. Bug 668871 is tracking these leaks; if you see any like this please report them there.
- Speaking of which, that “heap-unclassified” number is still higher than we’d like, often in the 35–45% range. If you see a particular site that causes “heap-unclassified” to go unusually high, please report it here.
Finally, here’s the MemShrink bug count, with the changes since last week:
- P1: 24 (+6)
- P2: 49 (+5)
- P3: 29 (+4)
- Unprioritized: 2 (+0)
The increases look bad, but I think that’s not because progress isn’t being made. Rather, it’s a reflection that MemShrink efforts are still ramping up, and people are coming up with lots of new ideas and filing bugs for them. The upwards trend will probably continue for several more weeks.