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Adding 16 kb page size to Android

android-developers.googleblog.com

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Re: Adding 16 kb page size to Android

#41

Post by devit »

Seems pretty dubious to do this without adding support for having both 4KB and 16KB processes at once to the Linux kernel, since it means all old binaries break and emulators which emulate normal systems with 4KB pages (Wine, console emulators, etc.) might dramatically lose performance if they need to emulate the MMU.

Hopefully they don't actually ship a 16KB default before supporting 4KB pages as well in the same kernel.

Also it would probably be reasonable, along with making the Linux kernel change, to design CPUs where you can configure a 16KB pagetable entry to map at 4KB granularity and pagefault after the first 4KB or 8KB (requires 3 extra bits per PTE or 2 if coalesced with the invalid bit), so that memory can be saved by allocating 4KB/8KB pages when 16KB would have wasted padding.

Re: Adding 16 kb page size to Android

#42

Post by pantalaimon »

saagarjha wrote: post #30
andai wrote: post #22

Earlier quoted context omitted.

A lot of low level stuff is a lot slower on Windows, let alone the GUI. There's also entire blogs cataloging an abundance of pathological performance issues. The one I notice the most is the filesystem. Running Linux in VirtualBox, I got 7x the host speed for many small file operations. (On top of that Explorer itself has its own random lag.) I think a better question is how much performance are they leaving on the t…

None of this has to do with page size.

Death by 1000 cuts

Re: Adding 16 kb page size to Android

#43

Post by HeatrayEnjoyer »

jandrese wrote: post #17
evilduck wrote: post #13

Earlier quoted context omitted.

Question I wrote: > I encountered the typo "anablibg" in the sentence "I wonder how much help they had by asahi doing a lot of the kernel and ecosystem work anablibg 16k pages." What did they actually mean? GPT-4o and Sonnet 3.5 understood it perfectly. This isn't really a problem for the large models. For local small models: * Gemma2 9b did not get it and thought it meant "analyzing". * Codestral (22b) did not it ge…

Seems like there is a bit of a roll of the dice there. The ones that got it right may have just been lucky.

Ran it a few times in new sessions, 0 failures so far.

Re: Adding 16 kb page size to Android

#44

Post by mananaysiempre »

sweeter wrote: post #18
a1o wrote: post #7

> The very first 16 KB enabled Android system will be made available on select devices as a developer option. This is so you can use the developer option to test and fix > once an application is fixed to be page size agnostic, the same application binary can run on both 4 KB and 16 KB devices I am curious about this. When could an app NOT be agnostic to this? Like what an app must be doing to cause this to be noticea…

Wine doesn't work on 16 KB page size among other things.

This seems especially peculiar given Windows has a 64K mapping granularity.

Re: Adding 16 kb page size to Android

#45

Post by username81 »

devit wrote: post #41

Seems pretty dubious to do this without adding support for having both 4KB and 16KB processes at once to the Linux kernel, since it means all old binaries break and emulators which emulate normal systems with 4KB pages (Wine, console emulators, etc.) might dramatically lose performance if they need to emulate the MMU. Hopefully they don't actually ship a 16KB default before supporting 4KB pages as well in the same ke…

Shouldn't there be some kind of setting to change the page size per program? AFAIK AMD64 CPUs can do this.

Re: Adding 16 kb page size to Android

#46

Post by fouronnes3 »

devit wrote: post #41

Seems pretty dubious to do this without adding support for having both 4KB and 16KB processes at once to the Linux kernel, since it means all old binaries break and emulators which emulate normal systems with 4KB pages (Wine, console emulators, etc.) might dramatically lose performance if they need to emulate the MMU. Hopefully they don't actually ship a 16KB default before supporting 4KB pages as well in the same ke…

Could they upstream that or would that require a fork?

Re: Adding 16 kb page size to Android

#47

Post by nabla9 »

saagarjha wrote: post #31
monocasa wrote: post #2

I wonder how much help they had by asahi doing a lot of the kernel and ecosystem work anablibg 16k pages. RISC-V being fixed to 4k pages seems to be a bit of an oversight as well.

Probably very little, since the Android ecosystem is quite divorced from the Linux one.

Android kernel is a mainstream Linux kernel, with additional drivers, and other functionality.

Re: Adding 16 kb page size to Android

#48

Post by mgaunard »

devit wrote: post #41

Seems pretty dubious to do this without adding support for having both 4KB and 16KB processes at once to the Linux kernel, since it means all old binaries break and emulators which emulate normal systems with 4KB pages (Wine, console emulators, etc.) might dramatically lose performance if they need to emulate the MMU. Hopefully they don't actually ship a 16KB default before supporting 4KB pages as well in the same ke…

why does it break userland? if you need to know the page size, you should query sysconf SC_PAGESIZE.

Re: Adding 16 kb page size to Android

#49

Post by nullindividual »

andai wrote: post #22
jsheard wrote: post #19

Earlier quoted context omitted.

Makes me wonder how much performance Windows is leaving on the table with its primitive support for large pages. It does support them, but it doesn't coalesce pages transparently like Linux does, and explicitly allocating them requires special permissions and is very likely to fail due to fragmentation if the system has been running for a while. In practice it's scarcely used outside of server software which immediat…

A lot of low level stuff is a lot slower on Windows, let alone the GUI. There's also entire blogs cataloging an abundance of pathological performance issues. The one I notice the most is the filesystem. Running Linux in VirtualBox, I got 7x the host speed for many small file operations. (On top of that Explorer itself has its own random lag.) I think a better question is how much performance are they leaving on the t…

> The one I notice the most is the filesystem.

This is due to the extensible file system filter model in place; I'm not aware of another OS that implements this feature and is primarily used for antivirus, but can be used by any developer for any purpose.

It applies to all file systems on Windows.

DevDrive[0] is Microsoft's current solution to this.

> Meanwhile Win10 Explorer opens after a noticeable delay

This could be, again, largely due to 3rd party hooks (or 1st party software that doesn't ship with Windows) into Explorer.

[0] https://devblogs.microsoft.com/visualstudio/devdrive/

Re: Adding 16 kb page size to Android

#50

Post by akdev1l »

mgaunard wrote: post #48
devit wrote: post #41

Seems pretty dubious to do this without adding support for having both 4KB and 16KB processes at once to the Linux kernel, since it means all old binaries break and emulators which emulate normal systems with 4KB pages (Wine, console emulators, etc.) might dramatically lose performance if they need to emulate the MMU. Hopefully they don't actually ship a 16KB default before supporting 4KB pages as well in the same ke…

why does it break userland? if you need to know the page size, you should query sysconf SC_PAGESIZE.

Assumptions in the software.

Jemalloc is infamous for this: https://github.com/sigp/lighthouse/issues/5244

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