Re: [PATCH 3/8] selftests/mm: check MADV_COLD and MADV_PAGEOUT range handling

[Gregory Price <gourry@gourry.net>]

On Fri, Oct 16, 2026 at 09:22:54AM -0400, Gregory Price wrote:
> On Fri, Oct 16, 2026 at 05:47:57PM +0530, Sarthak Sharma wrote:
> > > +/*
> > > + * An unmapped gap in the range makes either hint fail with ENOMEM, after
> > > + * advising the mapped pages on both sides of the gap. Only MADV_PAGEOUT has
> > > + * an effect on those pages that the test can observe.
> > > + */
> > > +TEST_F(madvise, unmapped_gap_fails_after_advising)
> > > +{
> > > +	char *mapping, *control;
> > > +	bool swapped = false;
> > > +	int retry;
> > > +
> > > +	pin_to_current_cpu(_metadata);
> > > +
> > > +	/* Make sure MADV_PAGEOUT can swap at all before relying on it. */
> > > +	control = mmap(NULL, page_size, PROT_READ | PROT_WRITE,
> > > +		       MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> > > +	ASSERT_NE(control, MAP_FAILED);
> > > +	control[0] = 1;
> > > +	if (!pageout_until_swapped(_metadata, control, page_size,
> > > +				   self->pagemap_fd))
> > > +		SKIP(return, "MADV_PAGEOUT did not swap the page");
> > 
> > This test is checking for both MADV_COLD and MADV_PAGEOUT. So if we skip
> > here because we couldn't pageout, then we don't test for MADV_COLD
> > behaviour at all. Do we want it this way, or should the tests for both
> > of these be separate?
> > 
> 
> If swap is off, the behavior of COLD and PAGEOUT look pretty much the
> same, and we can't actually test them meaningfully.
> 
> We check that madvise(COLD) returns -1, but that's also largely
> meaningless if this initial pageout_until_swapped() call fails.
> 
> At least that's my thought.  If you think I should split it, I can.
> 

on second look, i will just move the cold checks above the rest, since
they're mostly checking failure paths.  those are mostly unchanging
regardless of swap status.

so basically no need to split, just a mild reorder.

~Gregory