[LTP] [PATCH v4] mmap22.c: Test for new MAP_DROPPABLE flag for mmap

[Jan Stancek]

On Wed, May 14, 2025 at 2:44 PM Li Wang <liwang@redhat.com> wrote:
>
> Jan Stancek <jstancek@redhat.com> wrote:
>
> > > > I'll have a closer look and try manually. At first glance at test, I
> > > > suspect compiler
> > > > doing something clever for:
> > > >                 for (;;)
> > > >                         *(char *)malloc(page_size) = 'B';
> > >
> > > Probably,  -O2 is the default in LTP compiling.
> > >
> > > Or, you could also try disabling KSM when testing mmap22.c to see if it helps.
> >
> > In case of my VM, it looks like it's able to swap faster than what's
> > needed to drop the allocation.
> > With this I get PASS right away:
> >
> > diff --git a/testcases/kernel/syscalls/mmap/mmap22.c
> > b/testcases/kernel/syscalls/mmap/mmap22.c
> > index 0e589dfab..56fe412d1 100644
> > --- a/testcases/kernel/syscalls/mmap/mmap22.c
> > +++ b/testcases/kernel/syscalls/mmap/mmap22.c
> > @@ -32,6 +32,7 @@ static void test_mmap(void)
> >
> >         cg_child = tst_cg_group_mk(tst_cg, "child");
> >         SAFE_CG_PRINTF(tst_cg, "memory.max", "%d", MEM_LIMIT);
> > +       SAFE_CG_PRINTF(tst_cg, "memory.swap.max", "%d", 1);
>
> Why not set it to 0 to disable it completely?

Yes, I realized that when I was preparing the patch :-).

>
> I guess we need to do it separately for both Cgroup v1 and v2.
>   - Cgroup-v1: set it to MEM_LIMIT.
>   - Cgroup-v2: set it to 0.
> FYI: https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/mem/oom/oom03.c#L33

Thanks for pointer, I'll add it also for cgroup v1.

>
> Anyway, testing will be much faster with this patch.
>
> --
> Regards,
> Li Wang
>