iOS and macOS share a program: jetsam. The tl;dr is that jetsam monitors memory usage, asks for memory when there isn't much free, and kills other programs that don't give back as much as was requested. This tool--a continuation from conradev's jetsamctl--serves to override the strict limits that jetsam sets on iOS devices with a simple command. All you need is a device with iOS 7 or later.
Type jetsamctl in a terminal to learn more about how to use. Here's some examples of what you can do:
Limit the Phone app to 48 MB of memory:
jetsamctl -l 48 MobilePhone
Set the priority of the Photos app to that of an iOS keyboard extension:
jetsamctl -p 8 MobileSlideShow
Here is a table of all of the priorities and their numerical values. A lower priority value obviously means that jetsam will bother it more.
| Priority | Value | Examples |
|---|---|---|
| Idle Head | -2 | |
| Default | -1 | |
| Idle | 0 | |
| Idle (Deferred) | 1 | |
| Background (Opportunistic) | 2 | |
| Background | 3 | |
| 4 | Apple Mail | |
| Phone | 5 | Phone app |
| UI Support | 8 | Keyboard extension |
| Foreground Support | 90 | Share extension |
| Foreground | 10 | Foreground application |
| Audio and Accessory | 12 | |
| Conductor | 13 | |
| Home | 16 | SpringBoard |
| Executive | 17 | |
| Important | 18 | |
| Critical | 19 | |
| Maximum | 21 |
Since iOS 16, all non-negative priorities has been multiplied by 10, so on iOS 16, the priority for SpringBoard is 160.
jetsamctl is available under the MIT license. See the LICENSE file for more info.