Free memory said 78%, and macOS still ran out of application memory

A developer fixed a memory-pressure guard in the open-source mac-yolo-safeguards project after a 48 GB Mac reported "out of application memory" while free memory still read 77–79 percent and swap sat at 14.4 of 15 GB. The revised check now flags swap as pressure only when at least 8 GB is in use and the swap area is mostly full, warning at 80 percent and going critical at 90 percent, and it also corrects a rounding bug that turned 89.5 percent into a critical 90. When memory is critical and no leftover agent processes remain, the guard shows a notice naming the reason and the three biggest memory owners, at most every 30 minutes.

On November 14 a 48 GB Mac showed "your system has run out of application memory" while a pile of coding agents was running. The odd part is that free memory had read 77 to 79 percent all morning. Swap was at 14.4 of 15 GB. Our guard had a rule that said swap size alone is never pressure, and for good reason. macOS adds swap files as it needs them and leaves cold pages in them, so a big swap number on a healthy Mac is common. We took that too far. That was the bug. "Large swap is not pressure" is true. "Nearly full swap is not pressure" is not. The fix The pressure check now treats swap as a signal only when both things hold: at least 8 GB is in use, and the swap area is mostly full. At 80 percent it warns, and at 90 percent it is critical. js const SWAP FULL MIN MB = 8192; const SWAP FULL WARN PCT = 80; const SWAP FULL CRITICAL PCT = 90; const swapFull = memory.swapUsedPct = null && memory.swapUsedMB = SWAP FULL MIN MB; if swapFull && memory.swapUsedPct = SWAP FULL CRITICAL PCT raise 'critical', swap is ${Math.round memory.swapUsedPct }% full ; else if swapFull && memory.swapUsedPct = SWAP FULL WARN PCT raise 'warn', swap is ${Math.round memory.swapUsedPct }% full ; The 8 GB floor matters. A 1.9 GB swap that is 95 percent full is just a small swap file, and we have a test that keeps it at normal. The second thing we found was a rounding bug. The percentage was rounded to a whole number when we read it, so 89.5 percent became 90 and tipped over into critical. We now keep the raw number for the comparison and round only when printing the reason. There is a test for 89.5 percent staying a warning and 79.6 percent staying normal. What the guard does about it Before this, the cleanup could only stop leftover agent processes. Now, if memory is critical and nothing is left to stop, it shows one notice that names the reason and the three biggest owners, for example "swap is 94% full 14378 MB ... most is held by Codex 15.5 GB 318 processes , Claude 8.5 GB 131 processes , Google Chrome 4.2 GB 40 processes ". It shows that at most every 30 minutes, and if macOS refuses to show the notification, the 30 minute timer is not started. Check your own Mac sysctl vm.swapusage memory pressure | tail -1 If the swap line shows several gigabytes used and close to the total ours was 14.4 of 15 GB , and memory pressure reports less than about 20 percent free, you are near the wall no matter what the free memory figure says. A small swap area that is nearly full, like 1.9 GB at 95 percent, is normal on its own. The guard is open source: https://github.com/IgorGanapolsky/mac-yolo-safeguards https://github.com/IgorGanapolsky/mac-yolo-safeguards