Tab Discarding and Reloading

Why are my tabs reloading?

Your device is out of memory. Like your Android phone or tablet, Chrome is silently closing background tabs in order to make memory available. When you click on one of those tabs it reloads.

What's taking up all my memory?

Open the Task manager (under Tools > Tools > Task manager, or hit Shift-Esc) to see the usage of tabs and extensions. about:memory has more detailed information.

How can I make it stop?

Close some tabs or uninstall extensions that take a lot of memory. If there's a specific tab you don't want discarded, right-click on the tab and pin it.

How does Chrome choose which tab to discard?

You can go to about:discards to see the current ranking of your tabs. It discards in this order:

1. Internal pages like new tab page, bookmarks, etc.
2. Tabs selected a long time ago
3. Tabs selected recently
4. Tabs playing audio
5. Apps running in a window
6. Pinned tabs
7. The selected tab

How often are users affected by this?

The majority of Chrome OS users have only one or two tabs open. Even users with more tabs open rarely run out of memory. Some users who run out of memory never see a reload (they log out without ever looking at a discarded tab). We have internal UMA metrics on all these conditions. Googlers tend to have large numbers of tabs open to complex web sites and tend to hit reloads more often.

Why doesn't Chrome do this on Mac / Windows / Goobuntu?

Those machines swap memory out to disk when they get low on resources. Changing tabs then slows down as the data is loaded from disk.

Why doesn't Chrome OS use swap?

This was a very early design decision. My understanding of the rationale is:

* Chrome OS doesn't want to wear out the SSD / flash chips by constantly writing to them.

* To preserve device security it would have to encrypt the swap, which increases the CPU and battery usage.

* Rather than slowing down by swapping, Chrome OS should run fast until it hits a wall, then discard data and keep running fast.

Why doesn't Chrome OS tell me that I'm out of memory?

This is an intentional UI design decision. My understanding of the rationale is:

* Phones and tablets silently discard pages

* Users shouldn't have to worry about managing memory

Why do we discard tabs instead of doing something else?

Well, we used to do something worse. When the machine ran out of memory the kernel out-of-memory killer would kill a renderer, which would kill a semi-random set of tabs. Sometimes this included the selected tab, so the user would see a sad tab page (specifically, He's dead, Jim.). The tab discarder only drops one tab at a time and tries to be smart about what it discards. We tried other approaches without much success. For example, forcing JavaScript garbage collection is too slow. Dropping various graphics caches only frees memory for a short amount of time. Part of the difficulty is that the response to low memory conditions needs to be fast, reliable and lead to a persistent decrease in memory consumption.

Is there a long-term plan for this issue?

Sometimes these issues are caused by memory leaks or bloat, which we fix. davemoore@ has been particularly good at finding Chrome OS memory problems. We also need to systematically reduce the amount of memory Chrome uses. People across the browser, renderer and graphics teams are working on this. We're also investigating zram (a kind of in-memory swap). At some point we may want to revisit the design decisions above.

Where can I find more detailed information about what we do in low memory situations?

See the out of memory design document.