Reducing FOOMs in the Facebook iOS app

Meta's iOS team faced a silent killer: crashes that left no trace, no stack trace, no clue. Just frustrated users and a mystery to solve.

Facebook's engineering team documented how they identified and reduced FOOMs (foreground out-of-memory events) in their iOS app. These crashes are invisible to traditional crash reporting because iOS simply terminates the app when memory runs out, leaving developers blind to the problem.

Key Takeaways

• Tracked six restart reasons to isolate OOMs through process of elimination
• Migrating from UIWebView to WKWebView dramatically reduced memory footprint
• Eliminating temporary 30MB allocations improved reliability by 30 percent
• Built custom C++ allocation tracker to monitor Objective-C object counts
• Automated regression detection using CT-Scan infrastructure for memory tracking

The method swizzling technique they used to build an in-app profiler reveals how deep they went to catch memory leaks.