Re: [PATCH] mm/madvise: reclaim isolated folios if PTE restart fails

[Gregory Price <gourry@gourry.net>]

On Wed, Sep 16, 2026 at 04:48:04PM +0200, David Hildenbrand (Arm) wrote:
> On 9/16/26 16:42, Gregory Price wrote:
> > On Wed, Sep 16, 2026 at 03:12:53PM +0100, Lorenzo Stoakes (ARM) wrote:
> >>>
> >>> Going to spend a little more time testing and tweaking before I post it.
> >>>
> >>> I've been working on a making more extensive unit tests for certain
> >>> parts of mm/ and this might be a good time to look at whether I can
> >>> introduce a piece of it.
> >>
> >> Nice, curious as to how?
> >>
> >> Have you tried the userland VMA tests btw? Not tooting my own horn so to
> >> speak :P but it's nice, though it comes at a bit of a cost in how the files
> >> have to be set up...
> >>
> > 
> > Yes, in fact I used that as a start for exploring how I might make other
> > components testable the same way.
> > 
> > "Stubs... stubs everywhere"
> > 
> > There's basically 4 testing mechanisms i explored:
> > 
> > 1) selftest
> > 2) Usermode Linux (UML)
> > 3) Userland stuff like VMA
> > 4) Linux Test Project (for syscall and ABI testing)
> > 
> > selftests are really limited and actually create a maintenance burden,
> > they're not real unit tests and are highly dependent on the actual
> > machine configuration which is super annoying.
> > 
> > But, lets take the page allocator as an example.
> > 
> > The only piece of the page allocator that "should" (cough, simplifying
> > here a bit) be machine specific is zone and node configurations... but
> > I'm not convinced that this should require a full VM to unit-test.
> 
> I told Brendan exactly that (try stubbing it) and he tried ... and had to give
> up at some point because it just wasn't feasible. ;)
> 

LLM go brrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr

I'll try to clean up my current pile and see what I can pull out for
some select components.  Something is better than literally nothing.

I'm trying to be careful about not causing a bigger maintenance burden
while also having some confidence in my own code.

~Gregory