Re: [PATCH v3 6/7] selftest/mm: ksm_functional_tests: test in mmap_and_merge_range() if anything got merged

[David Hildenbrand]

On 03.08.23 21:05, Peter Xu wrote:
> On Thu, Aug 03, 2023 at 04:32:07PM +0200, David Hildenbrand wrote:
> > Let's extend mmap_and_merge_range() to test if anything in the current
> > process was merged. range_maps_duplicates() is too unreliable for that
> > use case, so instead look at KSM stats.
> >
> > Trigger a complete unmerge first, to cleanup the stable tree and
> > stabilize accounting of merged pages.
> >
> > Note that we're using /proc/self/ksm_merging_pages instead of
> > /proc/self/ksm_stat, because that one is available in more existing
> > kernels.
> >
> > If /proc/self/ksm_merging_pages can't be opened, we can't perform any
> > checks and simply skip them.
> >
> > We have to special-case the shared zeropage for now. But the only user
> > -- test_unmerge_zero_pages() -- performs its own merge checks.
> >
> > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>

Hi Peter,

thanks for the review!

> Acked-by: Peter Xu <peterx@xxxxxxxxxx>
>
> One nitpick:
>
> > ---
> >   .../selftests/mm/ksm_functional_tests.c       | 47 +++++++++++++++++++
> >   1 file changed, 47 insertions(+)
> >
> > diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
> > index 0de9d33cd565..cb63b600cb4f 100644
> > --- a/tools/testing/selftests/mm/ksm_functional_tests.c
> > +++ b/tools/testing/selftests/mm/ksm_functional_tests.c
> > @@ -30,6 +30,7 @@
> >   static int ksm_fd;
> >   static int ksm_full_scans_fd;
> >   static int proc_self_ksm_stat_fd;
> > +static int proc_self_ksm_merging_pages_fd;
> >   static int ksm_use_zero_pages_fd;
> >   static int pagemap_fd;
> >   static size_t pagesize;
> > @@ -88,6 +89,22 @@ static long get_my_ksm_zero_pages(void)
> >   	return my_ksm_zero_pages;
> >   }
> >   
> > +static long get_my_merging_pages(void)
> > +{
> > +	char buf[10];
> > +	ssize_t ret;
> > +
> > +	if (proc_self_ksm_merging_pages_fd < 0)
> > +		return proc_self_ksm_merging_pages_fd;
>
> Better do the fds check all in main(), e.g. not all callers below considers
> negative values, so -1 can pass "if (get_my_merging_pages())" etc.

The two existing callers should be handling it correctly:

if (get_my_merging_pages() > 0)
	-> fail

if (val && !get_my_merging_pages()
	-> fail

Both will pass on negative values, unless I am missing something.

I tried to keep the test working also on older kernels where 
ksm_merging_pages does not exist yet (it's ~1 year old).


Anyhow, if you think it's better to make the test fail on these setups, 
I can change it.

--
Cheers,

David / dhildenb