Re: [PATCH v3 4/4] mm: pass the number of PTEs to move_pte()

[Imre Kaloz <kaloz@kernel.org>]

Hi David,

On 10/28/26 09:49, David Hildenbrand (Arm) wrote:
> But that's too complicated, requiring page table walks ....
> People running museum piece hardware and complaining about performance of mremap
> or memory reclaim should reconsider life choices.

I'm one of the museum folks myself, though more the kind who loves
running a modern kernel on old hardware than the kind who complains
about it :) A lot of these machines are still doing real work, and
these days not everyone can, or wants to, just buy a new computer.

Some of us spend our time keeping these platforms working, and I'm
not asking anyone else to carry that, which is why I tried to keep
all of it in sparc.

> So I'd say, make it as slow as you want while reducing core-MM complexity and
> not adding more arch complexity.

With C, move_pte() and __HAVE_ARCH_MOVE_PTE go away from
include/linux/pgtable.h and mm/mremap.c just like with A and B. The
walk lives in sparc's own flush_cache_range() and only runs on the
CPUs that need it.

B would be less sparc code, but every UltraSPARC I-IV machine would
pay 13-18% on reclaim for it, so I'd still lean towards C. If you feel
strongly about B, though, I'm happy to send that instead.


Best,
Imre