Re: [PATCH V12] mm/debug: Add tests validating architecture page table helpers

Catalin Marinas
2020-01-28T17:47:19Z

On Mon, Jan 27, 2020 at 09:11:53PM -0500, Qian Cai wrote:
> On Jan 27, 2020, at 8:28 PM, Anshuman Khandual <Anshuman.Khandual@arm.com> wrote:
> > This adds tests which will validate architecture page table helpers and
> > other accessors in their compliance with expected generic MM semantics.
> > This will help various architectures in validating changes to existing
> > page table helpers or addition of new ones.
[...]
> What’s the value of this block of new code? It only supports x86 and
> arm64 which are supposed to be good now. Did those tests ever find any
> regression or this is almost only useful for new architectures which
> only happened once in a few years?

The primary goal here is not finding regressions but having clearly
defined semantics of the page table accessors across architectures. x86
and arm64 are a good starting point and other architectures will be
enabled as they are aligned to the same semantics.

See for example this past discussion:

https://lore.kernel.org/linux-mm/20190628102003.GA56463@arrakis.emea.arm.com/

These tests should act as the 'contract' between the generic mm code and
the architecture port. Without clear semantics, some bugs may be a lot
subtler than a boot failure.

FTR, I fully support this patch (and I should get around to review it
properly; thanks for the reminder ;)).

--
Catalin