[PATCH v2 0/2] selftests: cgroup: Report failed checks in test_memcontrol

[Sebastian Chlad <sebastianchlad@gmail.com>]

test_memcontrol fails intermittently, but most of its checks fail
silently, so a "not ok" line gives no indication of how far off the
measured value was. This series makes those failures print the observed
and expected values. It does not change any threshold or pass/fail
behaviour.

Patch 1 converts the terminal tolerance checks to values_close_report(),
as was done for test_cpu in commit 4cdde87d723a ("selftests: cgroup: Use
values_close_report in test_cpu"). values_close() is kept where it is a
loop or retry condition, where a mismatch is expected.

Patch 2 reports the "memory.current < 50M" check in
alloc_pagecache_50M_check(). Because test_memcg_high() calls the same
helper expecting it to fail, it gets a quiet variant. An alternative
would be to pass the flag through the currently unused void *arg of
the cg_run() callback; I am happy to switch to that if preferred.

With patch 1 applied, we observe at times failures like these:

  not ok 3 test_memcg_min
  [FAIL] actual=18722816 expected=30408704 | diff=11685888 | limit=7369725 | tolerance=15% | actual_error=23.78%

  not ok 4 test_memcg_low
  [FAIL] actual=20852736 expected=30408704 | diff=9555968 | limit=7689210 | tolerance=15% | actual_error=18.64%

  not ok 4 test_memcg_low
  [FAIL] actual=14364672 expected=22020096 | diff=7655424 | limit=7276940 | tolerance=20% | actual_error=21.04%

These are the child memory.current checks in test_memcg_protection()
(expected ~29M and ~21M). Their tolerances were already raised in commit
d2def68ae06a ("selftests: memcg: increase error tolerance of child
memory.current check in test_memcg_protection()"), and the values above
still fall outside them. In the first case the child is about 38% below
the expected 29M. This series only makes such failures visible; whether
the expectations or the tolerances should change is left for a separate
discussion.

Changes in v2:
- Patch 1: pass the measured value first in the alloc_anon_50M_check()
  values_close_report() call, so that a failure prints actual and
  expected the right way round (reported by Sashiko AI review).

v1: https://lore.kernel.org/all/20260926034923.31718-1-sebastian.chlad@suse.com/

Sebastian Chlad (2):
  selftests: cgroup: Use values_close_report in test_memcontrol
  selftests: cgroup: Report memory.current shortfall in
    alloc_pagecache_50M_check

 .../selftests/cgroup/test_memcontrol.c        | 50 +++++++++++++------
 1 file changed, 36 insertions(+), 14 deletions(-)

-- 
2.51.0