New Feature Release - Memory Management! (Patreon)

Hey Patrons! We hope that you’re all healthy, staying safe, and finding interesting things to do while stuck at home! With our extra time indoors, and your generosity toward yuzu, several of us have been able to work on the project full time! And with that, we’ve got some pretty exciting updates for you to enjoy this weekend!

Today, we have a particularly major change for you: We’ve heard over and over again that some of our users have had problems with game stability and performance. Especially with regards to memory usage, you may know that it’s not terribly uncommon for yuzu to eat up 8GB, 16GB, or even more RAM. Over the past 2 months, we’ve been quietly rewriting all of yuzu’s memory management code, and today we’re ready to share that with our Patrons in yuzu Early Access. On average, you can expect this new release of yuzu to use 50% less RAM! 

You can try out this new release in the latest yuzu Early Access builds. Below shows the before and after memory usage for several popular titles, measured while in game:

This was accomplished by rewriting yuzu’s Virtual Memory Manager (VMM), the software component that allocates, maps, and frees memory that Switch games use. This is a part of the emulator that uses High Level Emulation (HLE) to replicate functionality of the Switch’s "Horizon" Operating System. Previously, yuzu used a rather simplified approach to the VMM, based on Citra 3DS Emulator. Citra’s approach has served us well in getting the emulator working, but it was really designed for a much simpler system that did not scale to the needs of Switch. 

In short, this old implementation would arbitrarily allocate and map host (your PC) memory on the fly, without respecting the guest (Nintendo Switch) memory layout. This could result in run-away host memory allocations that were never actually possible on a real Switch. Here is a more comprehensive before and after memory comparison for many popular Switch games in yuzu: 

With the new VMM implementation, we now more accurately implement and respect Switch’s memory layout. As a result, emulation should in general not exceed Switch’s 4GB of dedicated RAM, with the exception of games that eat memory for other purposes (for example, GPU, audio, and OS emulation may still push the emulator beyond this). That being said, you may now expect games to use 2GB to 4GB of RAM on average, rather than double that!

In addition to the memory improvements, we are excited to learn about any new games that might be fixed! In fact, the work on the new VMM is what led to Super Smash Bros. Ultimate being fixed in yuzu.

In parting – we’d like to tease with one other thing – the new VMM is a stepping stone for a major improvement to yuzu that many of you have been asking for. Expect a huge update on top of this in the coming weeks (or days maybe, we’ll leave you in suspense!)

As always – thank you for your support, and stay safe!

- The yuzu development team