On Fri, Oct 16, 2026 at 05:48:11PM +0530, Sarthak Sharma wrote:
> > +/*
> > + * The owner of a file may page out its clean page-cache pages. Run as an
> > + * unprivileged owner, so that capabilities cannot stand in for ownership.
> > + */
> > +TEST_F(madvise, pageout_evicts_owned_file_page)
> > +{
> > + char *mapping, *control;
> > +
> > + if (!geteuid() && !drop_privileges())
> > + SKIP(return, "could not drop privileges");
> > + pin_to_current_cpu(_metadata);
>
> Is there a reason why we are pinning to the current CPU here and not in
> the next two tests?
Oversight on my part. I added it where i got a failure, but didn't
carry it forward to the other tests.
> > + ASSERT_EQ(mapping[0], 0);
> > + ASSERT_EQ(mapping[page_size], 0);
> > + mapping[0] = 1;
>
> If both pages are on CPU 1's per CPU LRU batch here and then hte task
> migrates to CPU 2 here
>
> > +
> > + ASSERT_EQ(madvise(mapping, 2 * page_size, MADV_PAGEOUT), 0);
>
> Then this can cause lru_add_drain() on CPU 2, and therefore both pages
> do not reach the main LRU list. Thus they won't be reclaimed and the
> test can skip here since the CoW page wasn't swapped.
I think there are other corner cases here as well. So yes i'll set up
thei pinning - probably worth it to just pin the entire suite of tests.
My original set had a bunch of this tested more explicitly, but this is
really implementation details that are not worth the additional test
complexity. I think we can just rid ourselves of that and just pin
every test and make sure it does what we expect in that case.
>
> > + ASSERT_TRUE(pagemap_is_populated(self->pagemap_fd,
> > + mapping + page_size));
> > + swapped = pagemap_is_swapped(self->pagemap_fd, mapping);
> > + ASSERT_EQ(mapping[0], 1);
> > + ASSERT_EQ(mapping[page_size], 0);
> > + if (!swapped)
> > + SKIP(return, "MADV_PAGEOUT did not swap the COW page");
>
> Also, here we skip if we couldn't swap out the CoW page. Won't it make
> more sense to check with pageout_until_swapped() first if pages can be
> skipped, and then fail here if the CoW page wasn't skipped after all the
> retries, similar to how some other tests implement it?
>
Ah yeah good catch. I'll adjust like this:
/* Ensure pageout-swap actually works first with a control page */
control[0] = 1;
if (!pageout_until_swapped(_metadata, control, page_size,
self->pagemap_fd))
SKIP(return, "MADV_PAGEOUT did not swap the control page");
/* Run the actual test */
ASSERT_EQ(mapping[0], 0);
ASSERT_EQ(mapping[page_size], 0);
mapping[0] = 1;
ASSERT_TRUE(pageout_until_swapped(_metadata, mapping, 2 * page_size,
self->pagemap_fd));
ASSERT_TRUE(pagemap_is_populated(self->pagemap_fd,
mapping + page_size));
ASSERT_EQ(mapping[0], 1);
ASSERT_EQ(mapping[page_size], 0);
~Gregory
