What does Jetsam really do?

Question

In a question I asked several months ago, I asked if the effect of Jetsam on memory usage can be observed. I answered my own question using instruments, finding that apps killed by Jetsam still had the same memory footprint that they had before they were terminated.

Even today, I still see jettisoned apps in the running task bar recently-used app list. I don't get any performance improvement unless I remove them myself, even after Jetsam has killed them.

If that's the case, what is the purpose of Jetsam and what is it doing (other than killing apps)? I don't see any benefits. Is this a bug?

Answer 1

Even today, I still see jettisoned apps in the running task bar. I don't get any performance improvement unless I remove them myself, even after Jetsam has killed them.

Poppycock. There's no such thing as a "running task bar". You're thinking of the list of recently-used apps. The presence of an app in this bar does not indicate that the app is still running, and removing killed apps from this bar has no effect on performance/memory. The only thing removing an app does from this bar that is beneficial is it kills the app if it was still running.

As for jetsammed apps, it's not surprising that the app will have the same memory footprint after it's relaunched. Apps are typically jetsammed because they're suspended and the foreground app needs more memory. The fact that an app is jetsammed does not indicate that the app was necessarily using an unacceptable amount of memory.