Transition to using 16 KB page sizes for Android apps and games
android-developers.googleblog.com
Transition to using 16 KB page sizes for Android apps and games
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Re: Transition to using 16 KB page sizes for Android apps and games
#2Weird. AFAIK 4K and 64K were the common ARM64 page sizes, and 16K was the odd "think different" one that Apple uses. No mention of 16K in the Linux kernel docs:
Re: Transition to using 16 KB page sizes for Android apps and games
#3Weird. AFAIK 4K and 64K were the common ARM64 page sizes, and 16K was the odd "think different" one that Apple uses. No mention of 16K in the Linux kernel docs: https://www.kernel.org/doc/html/next/arm64/memory.html
16K is the weird one in practice, but ARM says they are implementation-defined.
https://developer.arm.com/documentation/101811/0104/Translat...
Re: Transition to using 16 KB page sizes for Android apps and games
#4I can understand the desire for google to want devs to recompile their apps, but I don't see the need to dump old apps from the app store... who cares if an old app that works wastes 12k if it only needs a single 4k page?
Re: Transition to using 16 KB page sizes for Android apps and games
#5I can understand the desire for google to want devs to recompile their apps, but I don't see the need to dump old apps from the app store... who cares if an old app that works wastes 12k if it only needs a single 4k page?
I am not familiar with Android, but Linux ELF binaries that specify 4KB alignment will not work on systems with 16KB page sizes, since the ELF interpreter will refuse to load them. This hit me recently when trying to run a 32-bit binary on a Linux ARM system that had 16KB size pages, since the 32-bit OpenSSL libraries specified 4KB alignment. Presumably, this was done for maximizing entropy available to ASLR, but it breaks the binaries when the page size increases.
In any case, I assume that there is something similar affecting Android.
Re: Transition to using 16 KB page sizes for Android apps and games
#6Weird. AFAIK 4K and 64K were the common ARM64 page sizes, and 16K was the odd "think different" one that Apple uses. No mention of 16K in the Linux kernel docs: https://www.kernel.org/doc/html/next/arm64/memory.html
The 64-bit kernel shipped for the Raspberry Pi 5 uses 16KB pages.
Re: Transition to using 16 KB page sizes for Android apps and games
#7I can understand the desire for google to want devs to recompile their apps, but I don't see the need to dump old apps from the app store... who cares if an old app that works wastes 12k if it only needs a single 4k page?
Apps that expect 4K pages will try to enforce memory protections at that granularity.
Re: Transition to using 16 KB page sizes for Android apps and games
#8I used to work closely with the Android team at Unity, and in my experience, shifting large native codebases to a new page size often uncovers subtle runtime assumptions beyond just replacing hardcoded constants like PAGE_SIZE. I’m optimistic Google’s tooling will help a lot, but interested about how effectively it catches these more nuanced compatibility issues like custom allocators or memory pooling tuned for 4K boundaries.
Re: Transition to using 16 KB page sizes for Android apps and games
#9I can understand the desire for google to want devs to recompile their apps, but I don't see the need to dump old apps from the app store... who cares if an old app that works wastes 12k if it only needs a single 4k page?
I am not familiar with Android, but Linux ELF binaries that specify 4KB alignment will not work on systems with 16KB page sizes, since the ELF interpreter will refuse to load them. This hit me recently when trying to run a 32-bit binary on a Linux ARM system that had 16KB size pages, since the 32-bit OpenSSL libraries specified 4KB alignment. Presumably, this was done for maximizing entropy available to ASLR, but it…
Page size impacts page permissions; it's not a matter of wasting 12k, it's that with 4kb pages you're allowed to have a consecutive 8kb region with different permissions. 16kb pages can't do that without segfaulting every time memory is used "wrong", and trying to fix that up transparently would be a nightmare.
Re: Transition to using 16 KB page sizes for Android apps and games
#10Earlier quoted context omitted.
I am not familiar with Android, but Linux ELF binaries that specify 4KB alignment will not work on systems with 16KB page sizes, since the ELF interpreter will refuse to load them. This hit me recently when trying to run a 32-bit binary on a Linux ARM system that had 16KB size pages, since the 32-bit OpenSSL libraries specified 4KB alignment. Presumably, this was done for maximizing entropy available to ASLR, but it…
Page size impacts page permissions; it's not a matter of wasting 12k, it's that with 4kb pages you're allowed to have a consecutive 8kb region with different permissions. 16kb pages can't do that without segfaulting every time memory is used "wrong", and trying to fix that up transparently would be a nightmare.
> 16kb pages can't do that without segfaulting every time memory is used "wrong", and trying to fix that up transparently would be a nightmare.
I would natively imagine the kernel could trap that and remap on the fly, at the tiny cost of murdering performance. Is that untrue, or is the perf so bad that it's not worth it?