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

[Catalin Marinas <catalin.marinas@xxxxxxx>]

On Tue, Jan 28, 2020 at 02:07:10PM -0500, Qian Cai wrote:
> On Jan 28, 2020, at 12:47 PM, Catalin Marinas <catalin.marinas@xxxxxxx> wrote:
> > 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.
> 
> This still does not answer the fundamental question. If this test is
> simply inefficient to find bugs,

Who said this is inefficient (other than you)?

> who wants to spend time to use it regularly? 

Arch maintainers, mm maintainers introducing new macros or assuming
certain new semantics of the existing macros.

> If this is just one off test that may get running once in a few years
> (when introducing a new arch), how does it justify the ongoing cost to
> maintain it?

You are really missing the point. It's not only for a new arch but
changes to existing arch code. And if the arch code churn in this area
is relatively small, I'd expect a similarly small cost of maintaining
this test.

If you only turn DEBUG_VM on once every few years, don't generalise this
to the rest of the kernel developers (as others pointed out, this test
is default y if DEBUG_VM).

Anyway, I think that's a pointless discussion, so not going to reply
further (unless you have technical content to add).

-- 
Catalin