[LTP] [RFC] [PATCH] move_pages12: Allocate and free hugepages prior the test

[Jan Stancek]

----- Original Message -----
> Hi!
> > > I've got a hint from our kernel devs that the problem may be that the
> > > per-node hugepage pool limits are set too low and increasing these
> > > seems to fix the issue for me. Apparently the /proc/sys/vm/nr_hugepages
> > > is global limit while the per-node limits are in sysfs.
> > > 
> > > Try increasing:
> > > 
> > > /sys/devices/system/node/node*/hugepages/hugepages-2048kB/nr_hugepages
> > 
> > I'm not sure how that explains why it fails mid-test and not immediately
> > after start. It reminds me of sporadic hugetlbfs testsuite failures
> > in "counters" testcase.
> 
> Probably some kind of lazy update / deffered freeing that still accounts
> for freshly removed pages.

That was my impression as well.

> 
> > diff --git a/testcases/kernel/syscalls/move_pages/move_pages12.c
> > b/testcases/kernel/syscalls/move_pages/move_pages12.c
> > index 443b0c6..fe8384f 100644
> > --- a/testcases/kernel/syscalls/move_pages/move_pages12.c
> > +++ b/testcases/kernel/syscalls/move_pages/move_pages12.c
> > @@ -84,6 +84,12 @@ static void do_child(void)
> >                         pages, nodes, status, MPOL_MF_MOVE_ALL));
> >                 if (TEST_RETURN) {
> >                         tst_res(TFAIL | TTERRNO, "move_pages failed");
> > +                       system("cat
> > /sys/devices/system/node/node*/hugepages/hugepages-2048kB/nr_hugepages");
> > +                       system("cat
> > /sys/devices/system/node/node*/hugepages/hugepages-2048kB/free_hugepages");
> >                         break;
> >                 }
> >         }
> 
> Well that is a few forks away after the failure, if the race window is
> small enough we will never see the real value but maybe doing open() and
> read() directly would show us different values.

For free/reserved, sure. But is the number of reserved huge pages on
each node going to change over time?

---

I was running with 20+20 huge pages over night and it hasn't failed
single time. So I'm thinking we allocate 3+3 or 4+4 to avoid any
issues related to lazy/deffered updates.

Regards,
Jan