"Your system has run out of application memory" on Mac: what it means and what to quit

What "your system has run out of application memory" actually means

macOS manages memory in layers. First it uses your RAM. When that is close to full, it compresses the memory of apps you are not actively using, which can roughly halve their footprint. When compression is not enough, it writes the least-used pages to a swap file on the SSD and reads them back when needed. This dialog appears when all three layers are full: RAM is taken, compressed memory is at its limit, and the swap file has grown as large as the free disk space and the kernel's own limits allow. At that point macOS cannot give any process more memory, so it stops the apps it can and asks you to choose.

That is why the dialog is not the same as "your Mac has 8 GB and you opened too many apps". Plenty of 8 GB Macs run all day in the yellow without ever seeing it. To get all the way to the dialog, something has usually gone wrong: one process has kept asking for memory and never giving it back. In software terms that is a leak. In practical terms it is one app that is ten times its normal size, and the moment you quit it the whole Mac comes back.

The companion number is Memory Pressure, the graph at the bottom of Activity Monitor's Memory tab. Green is fine, yellow means compression and swap are in play, red means the system is struggling. The dialog appears at the far end of red. The memory pressure guide explains the graph; this page is about what to do when you have gone past it.

What to click in the dialog

The dialog lists your open apps with the biggest memory user at the top, and it offers Force Quit. Pick the top entry and Force Quit it. You lose unsaved work in that one app, and nothing else. If the top entry is your browser, that is almost always right: one tab is usually the problem, and the browser will offer to restore your tabs on relaunch. Just do not restore the tab that caused it.

Do not click the dialog away and carry on. Some people do, and the Mac limps along for another minute before the dialog returns or an app crashes. Do not start opening and closing random windows either; by the time the dialog is up, there is no slack left, and every action you take needs memory it does not have. Quit the top app, let the Mac breathe for ten seconds, and then go and look at what happened.

If the Mac is so stuck that the dialog itself does not respond, hold the power button until the Mac turns off, wait a few seconds, and turn it back on. That is a hard reset, and it is safe for the hardware. You lose unsaved work in every app, which is the cost of waiting too long.

What a typical leak day looks like

Here is the pattern that ends in the dialog, drawn from what people describe in the forum threads and from watching Macs over a working day. The times are illustrative; the shape is what to recognize.

The timeline is why "I was only doing the same things as always" is such a common line in these threads. You were. One of the things you always do has a leak in it, and the dialog is just the moment the Mac could no longer hide it. One Apple Community poster with a 16 GB M2 Air described swap that "grows to crazy levels like 30GB of SWAP used for the exact same apps and browser tabs open", which is exactly this shape.

How do I find which app is using all the memory? Activity Monitor, Memory tab

Open Activity Monitor (⌘Space, type "Activity Monitor"). Click the Memory tab, then click the Memory column header so the biggest number is on top. The top five lines tell the story.

What normal looks like at the top of that list: your browser's processes totaling 2 to 6 GB across many entries, WindowServer at 1 to 2 GB, your biggest creative or developer app at a few gigabytes, then everything else well under 1 GB. The Memory column is each process's footprint: its own dirty memory plus what it has in compressed memory and swap, which is why it is the right column to sort by.

What a leak looks like: one entry that is three, five or ten times its normal size and still climbing when you check again in five minutes. The three usual shapes:

• A browser renderer. Chrome shows "Google Chrome Helper (Renderer)", Safari shows "Safari Web Content", each one a tab or a group of tabs. One of them is huge. The browser's own task manager (Chrome: Window, Task Manager; Safari: Develop menu) names the tab. Close that tab. The which tab uses memory guide walks through both browsers.
• One app. Video editors, design tools, Electron apps and chat clients all have had leaking versions. If a single app is at 10 GB and you are not doing anything that needs 10 GB, quit it and reopen it. Update it if a newer version exists.
• WindowServer. The process that draws the screen. It normally sits at 1 to 2 GB and grows with open windows. When it reaches 5, 10 or more gigabytes and closing windows does not bring it down, the fix is to log out and back in, which restarts it without a full reboot. Hacker News threads on this have people reporting it at tens of gigabytes after long uptimes; one noted that "closing windows does not help much at all" once it has got that far, and another that "reboots appear to be the only real solution". Log out first; reboot if that does not do it.

Check your own memory pressure

Enter the figures from the bottom of your Activity Monitor Memory tab (Physical Memory, Memory Used, Swap Used, Compressed) and this tells you how close you are to the dialog and whether the problem is load or a leak.

Swap Used on its own is not the warning sign. A Mac that has been up for a week can show several gigabytes of swap and run perfectly, because that swap holds pages nothing has asked for in days. Swap that is growing while you watch, with pressure in the yellow, is the sign.

What to do about it, in order

1. Force Quit the top app in the dialog

   Usually the browser. This gives the Mac immediate room. Do not restore the tab that caused it if the browser offers to reopen your session.

2. Open Activity Monitor, Memory tab, sort by Memory

   Look for the one entry that is far bigger than normal. Browser renderer, a single app, or WindowServer above 5 GB are the three usual answers.

3. Quit and reopen the grower

   Quitting an app releases everything it had. Reopening it starts it at its normal size. If it climbs again within an hour, the leak is in that app, and you need the update or a different tool for that task.

4. If WindowServer is the grower, log out and back in

   Apple menu, Log Out. This restarts WindowServer without a full reboot. Close as many windows and tabs as you can first so it starts small.

5. Restart

   Swap goes to zero, compressed memory is released, every leak is reset. If you have been up for more than a week, restart before doing anything else and see whether the dialog comes back at all.

6. Free disk space if you are under 10 to 15 percent

   Swap lives on the startup disk. A nearly full disk means a small swap ceiling, which brings the dialog on sooner. The System Data guide covers the safe order for freeing space.

7. Update macOS and the app that keeps growing

   Leaks get fixed in point releases, both in macOS (WindowServer has had several) and in apps. Software Update in System Settings, then the App Store or the app's own updater.

Why 8 GB Macs see this more

An 8 GB Mac has less headroom at every layer. macOS itself and WindowServer take a chunk before you open anything; one Apple Community poster who booted into Safe Mode "found that there is only 4 of the 8 GB available to start with." A modern browser with a dozen tabs can take 3 to 4 GB. So an 8 GB Mac is already compressing and swapping during ordinary use, and a Hacker News commenter summed it up: "Again it comes down to the fact that 8GB means you are almost guaranteed to be on swap." That is fine on its own. macOS is good at it, and most 8 GB Macs feel fast most of the time.

The difference is how much a leak has to grow before it hits the wall. On a 32 GB Mac, a browser leaking to 11 GB is an annoyance you may never notice. On an 8 GB Mac, the same leak brings up the dialog by mid-afternoon. So the dialog on an 8 GB Mac does not always mean something is broken; sometimes it just means the same leak reached the limit faster. The fixes are the same, with two additions: keep fewer tabs open as a habit, and be quicker to quit apps you are not using rather than leaving them in the Dock. The web is the usual pressure point; as one poster put it, "there are too many websites which apparently shove large amounts of Javascript code into Safari-used memory."

Whether you need a bigger Mac is a separate question. If the dialog appears only after a specific app has been open all day, it is that app. If memory pressure is yellow within half an hour of a restart with only your normal work open, and you do that work every day, then 8 GB is genuinely the limit for your workload. Do not buy a memory cleaner app to postpone that decision; the memory cleaner apps page explains why they cannot help.

How to stop it coming back

Four habits cover almost every case. Restart once a week, or at least whenever Activity Monitor shows more than a few gigabytes of swap after a day of use. Keep an eye on the one app that has caused the dialog before; if it is at twice its normal size, quit and reopen it before lunch rather than after. Treat browser tabs as the memory cost they are: pinned tabs and background web apps keep their renderer processes alive, and Eclectic Light measured Safari at "an average of more than 120 MB per tab" even before a page does anything. And keep 10 to 15 percent of the disk free so swap has room.

If you want this watched rather than remembered, Safe to Quit tracks each process's memory over hours and flags the ones that grow, which is exactly the shape a leak has and exactly what a single glance at Activity Monitor misses. Either way, the point is to catch the grower at 14:30 on the timeline above, when quitting it costs nothing, rather than at 16:40, when the dialog chooses for you.