linux-kernel - Re: [linus:master] [memcg] 1813e51eec: kernel-selftests.cgroup.test_kmem.test_kmem_memcg

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Date:   Thu, 1 Dec 2022 11:16:34 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     kernel test robot <yujie.liu@...el.com>
Cc:     Shakeel Butt <shakeelb@...gle.com>, oe-lkp@...ts.linux.dev,
        lkp@...el.com, Andrew Morton <akpm@...ux-foundation.org>,
        kernel test robot <oliver.sang@...el.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>,
        Feng Tang <feng.tang@...el.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Muchun Song <songmuchun@...edance.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Koutný <mkoutny@...e.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [linus:master] [memcg] 1813e51eec:
 kernel-selftests.cgroup.test_kmem.test_kmem_memcg_deletion.fail

On Thu 01-12-22 16:05:44, kernel test robot wrote:
> Greeting,
> 
> FYI, we noticed kernel-selftests.cgroup.test_kmem.test_kmem_memcg_deletion.fail due to commit (built with gcc-11):
> 
> commit: 1813e51eece0ad6f4aacaeb738e7cced46feb470 ("memcg: increase MEMCG_CHARGE_BATCH to 64")
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
> 
> [test failed on linux-next/master 700e0cd3a5ce6a2cb90d9a2aab729b52f092a7d6]
> 
> in testcase: kernel-selftests
> version: kernel-selftests-x86_64-2ed09c3b-1_20221128
> with following parameters:
> 
> 	group: cgroup
> 
> test-description: The kernel contains a set of "self tests" under the tools/testing/selftests/ directory. These are intended to be small unit tests to exercise individual code paths in the kernel.
> test-url: https://www.kernel.org/doc/Documentation/kselftest.txt
> 
> on test machine: 128 threads 2 sockets Intel(R) Xeon(R) Platinum 8358 CPU @ 2.60GHz (Ice Lake) with 128G memory
> 
> caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):
> 
> 
> # memory.current = 40161280
> # slab + anon + file + kernel_stack = 14478624
> # slab = 13453184
> # anon = 0
> # file = 0
> # kernel_stack = 0
> # pagetables = 0
> # percpu = 1025440
> # sock = 0
> # not ok 2 test_kmem_memcg_deletion  <--
> # ok 3 test_kmem_proc_kpagecgroup
> # ok 4 test_kmem_kernel_stacks
> # ok 5 test_kmem_dead_cgroups
> # ok 6 test_percpu_basic
> not ok 2 selftests: cgroup: test_kmem # exit=1

IIUC we need this
diff --git a/tools/testing/selftests/cgroup/test_kmem.c b/tools/testing/selftests/cgroup/test_kmem.c
index 22b31ebb3513..1d073e28254b 100644
--- a/tools/testing/selftests/cgroup/test_kmem.c
+++ b/tools/testing/selftests/cgroup/test_kmem.c
@@ -24,7 +24,7 @@
  * the maximum discrepancy between charge and vmstat entries is number
  * of cpus multiplied by 32 pages.
  */
-#define MAX_VMSTAT_ERROR (4096 * 32 * get_nprocs())
+#define MAX_VMSTAT_ERROR (4096 * 64 * get_nprocs())
 
 
 static int alloc_dcache(const char *cgroup, void *arg)

But honestly, I am rather dubious of tests like this one. Does it really
give us any useful testing coverage?
-- 
Michal Hocko
SUSE Labs