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

[Wei Gao]

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?

Thanks for your such quick feedback :)
> 
> 
> 
> > > or, set `overcommit_memory` to 2 to prevent the OOM from occurring.
> > >     echo 2 > /proc/sys/vm/overcommit_memory
> > I have tried this option, oom still happen.
> >
> 
> Well, it looks like overcommit controlled by overcommit_memory is
> allowed for the entire system, not just the Cgroup.
> 
> 
> -- 
> Regards,
> Li Wang