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

[Li Wang]

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?
>
> --- 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);

>

-- 
Regards,
Li Wang