undefined | Better HN

0 pointssanxiyn2y ago0 comments

For example, Windows kernel's write watch feature is useful for writing a GC. Linux lacked (and as far as I know, still lacks) this feature, so Microsoft had to rewrite .NET runtime.

https://devblogs.microsoft.com/dotnet/working-through-things...

0 comments

kouteiheika2y ago

> Linux lacked (and as far as I know, still lacks) this feature

AFAIK it is possible to do this on Linux (either through mprotect + SIGSEGV or userfaultfd) but it's slow. But there's a work-in-progress patch that the Collabora folks (probably on a contract from Valve if I'd had to guess, as some games do use this) are working on which will add a new fast way of doing this.

sanxiynOP2y ago

userfaultfd was ~2015 (https://lwn.net/Articles/636226/), so Microsoft couldn't use it at the time. It could be better, but yes, Linux is making progress.

Even in current form, userfaultfd is useful for GC, so Linux's lack of the feature in 2015 was unfortunate. Android 13 added a new GC taking advantage of userfaultfd: https://android-developers.googleblog.com/2022/08/android-13....

> A new garbage collector based on the Linux kernel feature userfaultfd is coming to ART on Android 13... The new garbage collector... leading to as much as ~10% reduction in compiled code size.

j / k navigate · click thread line to collapse