Re: [PATCH 2/4] ARM: Disable HIGHPTE on PREEMPT_RT kernels

Sebastian Andrzej Siewior
2024-12-11T14:04:05Z

On 2024-12-11 14:48:11 [+0100], To Arnd Bergmann wrote:
> I guess if you have boxes with 4GiB+ and can proof that the performance
> improves without HIGHPTE (since you don't have to map the page table).
> The question is then how much of low mem has to be used instead and when
> does it start to hurt.

Some numbers have been been documented in commit
14315592009c1 ("x86, mm: Allow highmem user page tables to be disabled at boot time")

and I would like cite:
| We could probably handwave up an argument for a threshold at 16G of total
| RAM.

which means HIGHPTE would make sense with >= 16GiB of memory.

Sebastian