[LTP] [PATCH v1] swapon01.c: Apply a margin to avoid oom

[Wei Gao]

On Fri, Mar 15, 2024 at 12:19:52PM +0800, Li Wang wrote:
> On Fri, Mar 15, 2024 at 12:09 PM Li Wang <liwang@redhat.com> wrote:
> 
> >
> >
> > On Fri, Mar 15, 2024 at 11:44 AM Wei Gao <wegao@suse.com> wrote:
> >
> >> On Fri, Mar 15, 2024 at 11:17:01AM +0800, Li Wang wrote:
> >> > On Fri, Mar 15, 2024 at 9:30 AM Wei Gao <wegao@suse.com> wrote:
> >> >
> >> > > On Thu, Mar 14, 2024 at 02:40:40PM +0800, Li Wang wrote:
> >> > > > Hi Wei,
> >> > > >
> >> > > > On Thu, Mar 14, 2024 at 9:33 AM Wei Gao via ltp <ltp@lists.linux.it
> >> >
> >> > > wrote:
> >> > > >
> >> > > > > During our test i find a oom error during test which triggered by
> >> > > > > tst_pollute_memory.
> >> > > > >
> >> > > > > kernel:
> >> > > > >
> >> > >
> >> oom-kill:constraint=CONSTRAINT_MEMCG,nodemask=(null),cpuset=/,mems_allowed=0-1,oom_memcg=/ltp/test-9552,task_memcg=/ltp/test-95520
> >> > > > > kernel: Memory cgroup out of memory: Killed process 9575
> >> (swapon01)
> >> > > > > total-vm:1051484kB, anon-rss:1046572kB, file-rss:1280kB,
> >> shmem-rss:0k0
> >> > > > >
> >> > > > > Signed-off-by: Wei Gao <wegao@suse.com>
> >> > > > > ---
> >> > > > >  testcases/kernel/syscalls/swapon/swapon01.c | 4 +++-
> >> > > > >  1 file changed, 3 insertions(+), 1 deletion(-)
> >> > > > >
> >> > > > > diff --git a/testcases/kernel/syscalls/swapon/swapon01.c
> >> > > > > b/testcases/kernel/syscalls/swapon/swapon01.c
> >> > > > > index d406e4bd9..357992525 100644
> >> > > > > --- a/testcases/kernel/syscalls/swapon/swapon01.c
> >> > > > > +++ b/testcases/kernel/syscalls/swapon/swapon01.c
> >> > > > > @@ -41,7 +41,9 @@ static void setup(void)
> >> > > > >         make_swapfile(SWAP_FILE, 10, 0);
> >> > > > >
> >> > > > >         SAFE_CG_PRINTF(tst_cg, "cgroup.procs", "%d", getpid());
> >> > > > > -       SAFE_CG_PRINTF(tst_cg, "memory.max", "%lu", TESTMEM);
> >> > > > > +
> >> > > > > +       /* Apply a margin to avoid oom during tst_pollute_memory
> >> */
> >> > > > > +       SAFE_CG_PRINTF(tst_cg, "memory.max", "%lu", TESTMEM +
> >> > > TESTMEM/100);
> >> > > > >
> >> > > >
> >> > > > Even with a bit of margin added there is still not guarantee to
> >> avoid OOM
> >> > > > completely.
> >> > > >
> >> > > > As the Cgroup V1 and V2 track memory and swap in two ways, if the
> >> margin
> >> > > is
> >> > > > too large that might not make the swap happen which is not our
> >> > > expectation.
> >> > > >
> >> > > > So other method I can think of is to disable the OOM in Cgoup,
> >> > > >     echo 1 > memory.oom_control
> >> > > This option not exist in cgroupv2, it seems no direct oom control for
> >> > > cgroupv2
> >> > >
> >> >
> >> > Ok, which version (found the OOM issue) did you test on?
> >> mount | grep cgroup
> >> cgroup2 on /sys/fs/cgroup type cgroup2
> >> (rw,nosuid,nodev,noexec,relatime,nsdelegate,memory_recursiveprot)
> >> > Maybe here we have to split the control work into two parts (V1 and V2).
> >>
> >
> >
> >> How to disable OOM and also let swap action happen at the same time for
> >> cgroup V2?
> >>
> >
> > The Cgroup v2 does not provide a way to disable OOM inside directly.
> >
> > If we want to avoid OOM happening, just have to manage OOM behavior
> > in cgroup v2 by setting appropriate values for 'memory.max', 'memory.high',
> > and using 'memory.oom.group' to determine whether the OOM killer should
> > target individual processes or the whole Cgroup.
> >
> > After looking back at this case again, I guess the main reason is that the
> > swapfile is too small to bear the memory load, one direct method is like
> > you to enlarge the 'memory.max' value, but that still does not resolve
> > problems eventually.
> >
> > One possible solution is crate a bit larger swapfile for the test, and
> > unlimited
> > the swap out size. Can you try this patch on your system?
This not work.
> >
> > --- a/testcases/kernel/syscalls/swapon/swapon01.c
> > +++ b/testcases/kernel/syscalls/swapon/swapon01.c
> > @@ -38,10 +38,14 @@ static void verify_swapon(void)
> >  static void setup(void)
> >  {
> >         is_swap_supported(SWAP_FILE);
> > -       make_swapfile(SWAP_FILE, 10, 0);
> > +       make_swapfile(SWAP_FILE, 1024, 0);
> >
> >         SAFE_CG_PRINTF(tst_cg, "cgroup.procs", "%d", getpid());
> >         SAFE_CG_PRINTF(tst_cg, "memory.max", "%lu", TESTMEM);
> > +       if (TST_CG_VER_IS_V1(tst_cg, "memory"))
> > +               SAFE_CG_PRINTF(tst_cg, "memory.swap.max", "%lu", ~0UL);
> > +       else
> > +               SAFE_CG_PRINT(tst_cg, "memory.swap.max", "max");
> >  }
> >
> >  static struct tst_test test = {
> >
> 
> If this still does not work as expected, then we need plus additional
> policy to shrink the pollute memory size.
> 
> -       tst_pollute_memory(TESTMEM, 0x41);
> +       tst_pollute_memory(TESTMEM * 9/10, 0x41);
This works.
> 
> >
> 
> -- 
> Regards,
> Li Wang