Re: Minor page faults from memory compaction causing in-band transitions

On 01.04.26 01:14, Brandon Ho wrote:
> Hi Xenomai team,
> 
> I'm working on a real-time control application using Xenomai and we've been
> experiencing unexpected in-band transitions caused by minor page faults during
> kernel memory compaction. Even though our RT threads use mlockall(MCL_CURRENT |
> MCL_FUTURE) and we've pre-faulted memory, the kernel's compaction process seems
> to temporarily invalidate PTEs on our locked pages, causing faults when the RT
> thread accesses them.
> 
> Has this issue come up before? I'm wondering if there's a mechanism to reserve
> a section of RAM that's excluded from compaction/migration entirely, or if
> there are kernel/Xenomai configurations we should be using to prevent this.
> 
> Any guidance would be appreciated!

Memory migration as well as compaction are not compatible with
deterministic system behavior. Both Xenomai 3 and 4 should warn about
them, and you should disabling these features in your kernel.
Unfortunately, current kernels do not allow a more fine-grained control.

Jan

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