Chrome Speed

How to Deal with Android Size Alerts

Not all alerts should not have a bug created for them. Please read on...

Step 1: Identify the Commit

Monochrome.minimal.apks Alerts (Single Commit)

  • Zoom in on the graph to make sure the alert is not off-by-one
    • Replace &num_points=XXXX with &rev=COMMIT_POSITION in the URL.
    • It will be obvious from this whether or not the point is off. Use the “nudge” feature to correct it when this happens.

Monochrome.minimal.apks Alerts (Multiple Commits or Rolls)

  • Bisects will not help you.
  • For rolls, you can sometimes guess the commit(s) that caused the regression by looking at the android-binary-size trybot result for the roll commit.
  • For V8 rolls, try checking the V8 size graph to see if any jumps correspond with a CL in the roll.
  • Otherwise, use diagnose_bloat.py in a local Android checkout to build all commits locally and find the culprit.
    • If there were multiple commits due to a build breakage, use --apply-patch with the fixing commit (last one in the range).

Example:

 tools/binary_size/diagnose_bloat.py AFTER_GIT_REV --reference-rev BEFORE_GIT_REV --all [--subrepo v8] [--apply-patch AFTER_GIT_REV]
  • You can usually find the before and after revs in the roll commit message (example)
    • You may need to click through for the list of changes to find the actual first commit hash since some rollers (e.g. v8's) use an extra commit for tagging. In the linked example BEFORE_GIT_REV would actually be 876f37c and not c1dec05f.

SystemWebviewGoogle.apk Alerts

  • Check if the same increase happened in Monochrome.minimal.apks.
    • The goal is to ensure nothing creeps into webview unintentionally.

Step 2: File Bug or Silence Alert

  • If the commit message's Binary-Size: footer clearly justifies the size increase, silence the alert.
  • If the regression is < 100kb and caused by an AFDO roll, silence the alert.

Otherwise, file a bug (TODO: Make this template automatic):

  • Change the bug's title from X% to XXkb
  • Assign to commit author
  • Set description to (replacing bold parts):

Caused by “First line of commit message”

Commit: abc123abc123abc123abc123abc123abc123abcd

Link to size graph: https://chromeperf.appspot.com/report?sid=6269078068c45a41e23f5ee257da65d3f02da342849cdf3bde6aed0d5c61e450&num_points=10&rev=$CRREV
Link to trybot result: https://ci.chromium.org/p/chromium/builders/luci.chromium.try/android-binary-size/$TRYJOB_NUMBER

Debugging size regressions is documented at: https://chromium.googlesource.com/chromium/src/+/master/docs/speed/apk_size_regressions.md#Debugging-Apk-Size-Increase

Based on the trybot result: 20kb of native code, 8kb of pngs. (or some other explanation as to what caused the growth).

It's not clear to me whether or not this increase was expected.
Please have a look and either:

  1. Close as “Won't Fix” with a short justification, or
  2. Land a revert / fix-up.

Optional addition:

It typically takes about a week of engineering time to reduce binary size by 50kb so we'd really appreciate you taking some time exploring options to address this regression!

  • If the regression is >50kb, add ReleaseBlock-Stable M-## (next branch cut).*
  • If the regression was caused by a non-Googler, assign it to the closest Googler to the patch (e.g. reviewer). The size graphs are not public.

Debugging Apk Size Increase

It typically takes about a week of engineering time to reduce binary size by 50kb so it's important that an effort is made to address all new regressions.

Step 1: Identify what Grew

Figure out which file within the .apk increased (native library, dex, pak resources, etc.) by looking at the trybot results or size graphs that were linked from the bug (if it was not linked in the bug, see above).

See //docs/speed/binary_size/metrics.md for a description of high-level binary size metrics.

See //tools/binary_size/README.md for a description of binary size tools.

Step 2: Analyze

Growth is from Translations

  • There is likely nothing that can be done. Translations are expensive.
  • Close as Won't Fix.

Growth is from Native Resources (pak files)

  • Ensure compress="gzip" is used for all chrome: pages.
  • Look at the SuperSize reports from the trybot to look for unexpected resources, or unreasonably large symbols.

Growth is from Images

Growth is from Native Code

  • Look at the SuperSize reports from the trybot to look for unexpected symbols, or unreasonably large symbols.
  • If the diff looks reasonable, close as Won't Fix.
  • Otherwise, try to refactor a bit (e.g. move code out of templates).
  • If symbols are larger than expected, use the Disassemble() feature of supersize console to see what is going on.

Growth is from Java Code

  • Look at the SuperSize reports from the trybot to look for unexpected methods.
  • Ensure any new Java deps are as specific as possible.

Growth is from “other lib size” or “Unknown files size”

You Would Like Assistance

Step 3: Give Up :/

If you have spent O(days) trying to reduce the size overhead of your patch and are pretty sure that your implementation is efficient, then add a comment to the bug with the following:

  1. A description of where the size is coming from (show that you spent the time to understand why your code translated to a large binary size).
  2. What things you tried to reduce the size (show that you've at least read this doc and tried any relevant guidance).
  3. Why your commit is “worth” the size increase. For new features, feel free to link to a design doc (which presumably includes the motivation for adding the feature).

Close the bug as “Won't Fix”.

For Binary Size Sheriffs

Step 1: Check Work Queue Daily

  • Bugs requiring sheriffs to take a look at are labeled Performance-Sheriff and Performance-Size here.
  • After resolving the bug by finding an owner or debugging or commenting, remove the Performance-Sheriff label.

Step 2: Check Alerts Regularly

Step 3: Ping / Clear out Old Regression Bugs