[LTP] [PATCH v3] memcg/functional: fix memcg_failcnt intermittent timeout by disabling swap

[LTP] [PATCH v3] memcg/functional: fix memcg_failcnt intermittent timeout by disabling swap

[Xuewen Wang]

memcg_failcnt.sh tests the memory.failcnt counter by allocating
reclaimable memory (mmap-anon/mmap-file/shm) beyond a tiny cgroup
limit (1 page). It relies on the process being OOM-killed so that
signal_memcg_process()'s wait loop exits.

With swap enabled the kernel usually still OOM-kills the process,
but on arm64 reclaim (swap out) sometimes succeeds instead:
usage_in_bytes stays at the limit and the process keeps running,
so the wait loop times out (TBROK) intermittently.

Example failure on arm64 (kernel 6.6):
  memcg_failcnt 2 TBROK: timed out on memory.usage_in_bytes 4096 0 8192

Disable swap around the allocation and re-enable it afterwards,
mirroring what memcg_limit_in_bytes.sh already does for the same
reclaimable memory types.

Signed-off-by: Xuewen Wang <wangxuewen@kylinos.cn>
---
Changes in v2:
- Drop "2>/dev/null" from swapoff/swapon so that a failure to disable
  swap (or a missing swapoff binary) stays visible, instead of silently
  letting the intermittent timeout recur. Per the LTP AI review, the
  redirect hid the very error this fix relies on, and
  memcg_limit_in_bytes.sh does not redirect stderr either.

Changes in v3:
- Move swapoff to do_setup() and swapon to do_cleanup() per Li Wang,
  instead of wrapping each test iteration with swapoff/swapon in do_test().
---
 .../controllers/memcg/functional/memcg_failcnt.sh  | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/testcases/kernel/controllers/memcg/functional/memcg_failcnt.sh b/testcases/kernel/controllers/memcg/functional/memcg_failcnt.sh
index 3a02d16c2..93e8d4838 100755
--- a/testcases/kernel/controllers/memcg/functional/memcg_failcnt.sh
+++ b/testcases/kernel/controllers/memcg/functional/memcg_failcnt.sh
@@ -11,6 +11,20 @@
 MEMCG_TESTFUNC=do_test
 MEMCG_SHMMAX=1
 TST_TEST_DATA="--mmap-anon --mmap-file --shm"
+TST_SETUP=do_setup
+TST_CLEANUP=do_cleanup
+
+do_setup()
+{
+	memcg_setup
+	swapoff -a
+}
+
+do_cleanup()
+{
+	swapon -a
+	memcg_cleanup
+}
 
 do_test()
 {
-- 
2.25.1


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Re: [LTP] memcg/functional: fix memcg_failcnt intermittent timeout by disabling swap

[linuxtestproject.agent]

Hi Xuewen,

On Fri, Aug 7, 2026, Xuewen Wang wrote:
> memcg/functional: fix memcg_failcnt intermittent timeout by disabling swap

> +do_setup()
> +{
> +	memcg_setup
> +	swapoff -a
> +}

Could this use ROD so a failed swapoff aborts the test? swapoff can fail
when there is not enough memory to page the swap contents back in.
_tst_run_iterations() ignores the setup function's return status, so the
test proceeds with swap enabled and the original intermittent timeout
remains.

> +do_cleanup()
> +{
> +	swapon -a
> +	memcg_cleanup
> +}

Could cleanup restore only swap areas that were active before setup, and
only if swapoff was attempted? TST_DO_CLEANUP is set before do_setup(), so
a TCONF from memcg_setup() reaches this function before swapoff. swapon -a
can then activate previously inactive fstab entries. Conversely, dynamically
managed swap areas absent from fstab are disabled by swapoff -a but are not
restored by swapon -a.

Verdict - Needs revision

---
Note:

The agent can sometimes produce false positives although often its
findings are genuine. If you find issues with the review, please
comment this email or ignore the suggestions.

Regards,
LTP AI Reviewer

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Re: [LTP] [PATCH v3] memcg/functional: fix memcg_failcnt intermittent timeout by disabling swap

[Li Wang]

Patch merged, thanks!

-- 
Regards,
Li Wang

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Re: [LTP] memcg/functional: fix memcg_failcnt intermittent timeout by disabling swap

[Li Wang]

linuxtestproject.agent@gmail.com wrote:

> Hi Xuewen,
> 
> On Fri, Aug 7, 2026, Xuewen Wang wrote:
> > memcg/functional: fix memcg_failcnt intermittent timeout by disabling swap
> 
> > +do_setup()
> > +{
> > +	memcg_setup
> > +	swapoff -a
> > +}
> 
> Could this use ROD so a failed swapoff aborts the test? swapoff can fail
> when there is not enough memory to page the swap contents back in.
> _tst_run_iterations() ignores the setup function's return status, so the
> test proceeds with swap enabled and the original intermittent timeout
> remains.

Fair point that ignoring the return status defeats the purpose. But I'd
rather not TBROK on a swapoff failure, that's an environment limitation,
not a test failure. Especially swapoff here is an enhancement but not
a hard requirement for this test.

> 
> > +do_cleanup()
> > +{
> > +	swapon -a
> > +	memcg_cleanup
> > +}
> 
> Could cleanup restore only swap areas that were active before setup, and
> only if swapoff was attempted? TST_DO_CLEANUP is set before do_setup(), so
> a TCONF from memcg_setup() reaches this function before swapoff. swapon -a
> can then activate previously inactive fstab entries. Conversely, dynamically
> managed swap areas absent from fstab are disabled by swapoff -a but are not
> restored by swapon -a.

That is a bit over-engineering.

If an inactive fstab entry gets activated by swapon -a, that arguably
points to a misconfigured test host rather than something this test
should work around.


-- 
Regards,
Li Wang

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Re: [LTP] memcg/functional: fix memcg_failcnt intermittent timeout by disabling swap

[Andrea Cervesato via ltp]

Hi Li,

> Fair point that ignoring the return status defeats the purpose. But I'd
> rather not TBROK on a swapoff failure, that's an environment limitation,
> not a test failure. Especially swapoff here is an enhancement but not
> a hard requirement for this test.

I agree.

> That is a bit over-engineering.
> 
> If an inactive fstab entry gets activated by swapon -a, that arguably
> points to a misconfigured test host rather than something this test
> should work around.

And also here. Unfortunately we don't have enough data for shell tests,
so AI agent is not really working well in there..

Honestly I don't know how to fix this but adding more examples which
we don't have..

--
Andrea Cervesato
SUSE QE Automation Engineer Linux
andrea.cervesato@suse.com

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Re: [LTP] memcg/functional: fix memcg_failcnt intermittent timeout by disabling swap

[Li Wang]

Hi Xuewen, Andrea,

On Fri, Aug 07, 2026 at 05:34:49AM +0000, Andrea Cervesato wrote:
> Hi Li,
> 
> > Fair point that ignoring the return status defeats the purpose. But I'd
> > rather not TBROK on a swapoff failure, that's an environment limitation,
> > not a test failure. Especially swapoff here is an enhancement but not
> > a hard requirement for this test.
> 
> I agree.
> 
> > That is a bit over-engineering.
> > 
> > If an inactive fstab entry gets activated by swapon -a, that arguably
> > points to a misconfigured test host rather than something this test
> > should work around.
> 
> And also here. Unfortunately we don't have enough data for shell tests,
> so AI agent is not really working well in there..
> 
> Honestly I don't know how to fix this but adding more examples which
> we don't have..

No worries, AI agent being too strict in reviewing is not a bad thing.
It inspires me to think about something maybe in a different way.

Like this patch, I am now thinking if we can just limit it only
inside the cgroup:

--- a/testcases/kernel/controllers/memcg/functional/memcg_failcnt.sh
+++ b/testcases/kernel/controllers/memcg/functional/memcg_failcnt.sh
@@ -17,18 +17,17 @@ TST_CLEANUP=do_cleanup
 do_setup()
 {
        memcg_setup
-       swapoff -a
 }

 do_cleanup()
 {
-       swapon -a
        memcg_cleanup
 }

 do_test()
 {
        ROD echo $MEMORY_LIMIT \> memory.limit_in_bytes
+       ROD echo 0 \> memory.swappiness

        start_memcg_process $2 -s ${MEMORY_TO_ALLOCATE}
        ROD echo $MEMCG_PROCESS_PID \> tasks

@Xuewen, can you try this patch and see if it can solve your problem?

-- 
Regards,
Li Wang

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