1. How to view it on iPhone

Set up – General – analyze – analyze data – jetsamevent + log to start the system log.

2. How to view this kind of analysis log on MAC

1. Mobile link MAC

2. Open iTunes and click the phone icon

3. Click the sync button

The log will be synchronized to the following directory in MAC/users/username/library/logs/crashreporter/mobiledevice/

3. Analysis of logs:

Jetsamevent can help us check the memory usage of APP cleaned by the system.

{"bug_type":"298","timestamp":"2019-04-18 00:41:32.72 +0800","os_version":"iPhone OS 11.3.1 (15E302)","incident_id":"65385412-FCF1-4F8B-B9BA-7E3457FA2C43"}
{
  "crashReporterKey" : "cb1b46c9b29603987f13d3af5624dfe0891dcd8b",
  "kernel" : "Darwin Kernel Version 17.5.0: Tue Mar 13 21:32:11 PDT 2018; root:xnu-4570.52.2~8\/RELEASE_ARM64_T8010",
  "product" : "iPhone9,1",
  "incident" : "65385412-FCF1-4F8B-B9BA-7E3457FA2C43",
  "date" : "2019-04-18 00:41:32.67 +0800",
  "build" : "iPhone OS 11.3.1 (15E302)",
  "timeDelta" : 5,
  "memoryStatus" : {
  "compressorSize" : 50024,
  "compressions" : 79275112,
  "decompressions" : 61573914,
  "zoneMapCap" : 402653184,
  "largestZone" : "APFS_4K_OBJS",
  "largestZoneSize" : 13451264,
  "pageSize" : 16384,
  "uncompressed" : 120159,
  "zoneMapSize" : 113508352,
  "memoryPages" : {
    "active" : 29786,
    "throttled" : 0,
    "fileBacked" : 15361,
    "wired" : 26461,
    "anonymous" : 29604,
    "purgeable" : 33,
    "inactive" : 13602,
    "free" : 2391,
    "speculative" : 1577
  }
}
...
,
  "largestProcess" : "JD4iPhone",
  "genCounter" : 1,
  "processes" : [
  {
    "uuid" : "89715e1a-af5d-3c31-920a-b842f063e8be",
    "states" : [
      "daemon",
      "idle"
    ],
    "lifetimeMax" : 235,
    "age" : 1270330434891,
    "purgeable" : 0,
    "fds" : 50,
    "coalition" : 366,
    "rpages" : 115,
    "pid" : 19692,
    "idleDelta" : 3632517,
    "name" : "revisiond",
    "cpuTime" : 2.8573390000000001
  },

...

{
    "uuid" : "616cc66b-7c0b-3bd5-89ff-af63bd94dbb7",
    "states" : [
      "suspended"
    ],
    "lifetimeMax" : 14774,
    "age" : 82573963110,
    "purgeable" : 0,
    "fds" : 100,
    "coalition" : 4389,
    "rpages" : 10898,
    "pid" : 20571,
    "idleDelta" : 14614331251,
    "name" : "JD4iPhone",
    "cpuTime" : 268.98448000000002
  },

This is part of the jetsamevent log generated by iPhone 7. You can basically guess the meaning of the following log: “largestprocess”: “jd4iphone”, which means that jd4iphone uses the most temporary memory. If you don’t guess wrong, it should be JD app.

It occupies a memory page of “rpages”: 10898, “PageSize”: 16384, the size of each page is 16384/1024 = 16K, so the memory temporarily used by this application is 10898 * 16K = 170m “states”: [“suspended”], and its status is suspended.

The process of “UUID”: “89715e1a-af5d-3c31-920a-b842f063e8be” is idle, and it is a guard thread, which is generally maintained by the system. Although it only takes up “rpages”: 115, 115 memory pages.

4. Single application maximum available memory value of different models of mobile phones

Research on IOS oom principle of APP maximum memory usage limit