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

On Mon, Jan 27, 2020 at 09:11:53PM -0500, Qian Cai wrote:

On Jan 27, 2020, at 8:28 PM, Anshuman Khandual [off-list ref] wrote:

quoted

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/ (local)

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