OOM Crash in iOS Safari in the page editor as the pattern picker loads

[adamziel]

iOS safari sometimes crashes in the page editor as the pattern picker is loading. I can’t reliably reproduce it in a vanilla WordPress installation, but it happens every now and then. It’s much easier to reproduce in Playground where the memory usage is higher, making me think it’s an OOM error. It’s also consistent with other OOM symptoms I’ve seen in iOS Safari.

Steps to reproduce

1. In a vanilla WordPress installation, log in as admin and click the "New Page" link.
2. Wait for the pattern picker to show
3. Be lucky, witness the crash

Alternatively, reproduce the crash more reliably on https://playground.wordpress.net/ by visiting this link:

https://playground.wordpress.net/#ewogICJsYW5kaW5nUGFnZSI6ICIvd3AtYWRtaW4vcG9zdC1uZXcucGhwP3Bvc3RfdHlwZT1wYWdlIiwKICAibG9naW4iOiB0cnVlLAogICJzdGVwcyI6IFsKICAgIHsKICAgICAgInN0ZXAiOiAiZGVmaW5lV3BDb25maWdDb25zdHMiLAogICAgICAiY29uc3RzIjogewogICAgICAgICJQTEFZR1JPVU5EX0FMTE9XX1BBVFRFUk5fUElDS0VSIjogdHJ1ZQogICAgICB9LAogICAgICAibWV0aG9kIjogImRlZmluZS1iZWZvcmUtcnVuIgogICAgfQogIF0KfQ==

(Note it's not the default Playground. I had to disable that modal by default to Playground from crashing).

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[adamziel]

Here's some profiling data from Safari iOS.

Vanilla WP:

Playground WP:

The memory usage is high in both, but noticeably higher in Playground which is probably why it crashes more often there. The crash is still reproducible in both environments, though.

[adamziel]

@ellatrix said:

Hm well for a start it’s not paginated. Loads more than 10.
Hm, there are a lot of assets loaded in each frame, but should all be cached. It's probably the fact that each frame loads an editor on its own