Re: WARNING in try_charge

: [  366.454963] memory+swap: usage 0kB, limit 9007199254740988kB, failcnt 0
: [  366.461787] kmem: usage 0kB, limit 9007199254740988kB, failcnt 0
: [  366.467946] Memory cgroup stats for /ile0: cache:12KB rss:0KB rss_huge:0KB shmem:0KB mapped_file:0KB dirty:0KB writeback:0KB swap:0KB inactive_anon:0KB active_anon:0KB inactive_file:0KB active_file:0KB unevictable:0KB

There are only 3 pages charged to this memcg!

: [  366.487490] Tasks state (memory values in pages):
: [  366.492349] [  pid  ]   uid  tgid total_vm      rss pgtables_bytes swapents oom_score_adj name
: [  366.501237] [  23766]     0 23766    17620     8221   126976        0             0 syz-executor3
: [  366.510367] [  23767]     0 23767    17618     8218   126976        0             0 syz-executor2
: [  366.519409] Memory cgroup out of memory: Kill process 23766 (syz-executor3) score 8252000 or sacrifice child
: [  366.529422] Killed process 23766 (syz-executor3) total-vm:70480kB, anon-rss:116kB, file-rss:32768kB, shmem-rss:0kB
: [  366.540456] oom_reaper: reaped process 23766 (syz-executor3), now anon-rss:0kB, file-rss:32000kB, shmem-rss:0kB

The oom reaper cannot reclaim file backed memory  from a large part. I
assume this is are shared mappings which are living outside of memcg
because of the counter.

: [...]
: [  367.085870] oom-kill:constraint=CONSTRAINT_MEMCG,nodemask=(null),cpuset=/,mems_allowed=0,oom_memcg=/ile0,task_memcg=/ile0,task=syz-executor2,pid=23767,uid=0
: [  367.100073] memory: usage 112kB, limit 0kB, failcnt 1615
: [  367.105549] memory+swap: usage 0kB, limit 9007199254740988kB, failcnt 0
: [  367.112428] kmem: usage 0kB, limit 9007199254740988kB, failcnt 0
: [  367.118593] Memory cgroup stats for /ile0: cache:12KB rss:0KB rss_huge:0KB shmem:0KB mapped_file:0KB dirty:0KB writeback:0KB swap:0KB inactive_anon:0KB active_anon:0KB inactive_file:0KB active_file:0KB unevictable:0KB
: [  367.138136] Tasks state (memory values in pages):
: [  367.142986] [  pid  ]   uid  tgid total_vm      rss pgtables_bytes swapents oom_score_adj name
: [  367.151889] [  23766]     0 23766    17620     8002   126976        0             0 syz-executor3
: [  367.160946] [  23767]     0 23767    17618     8218   126976        0             0 syz-executor2
: [  367.169994] Memory cgroup out of memory: Kill process 23767 (syz-executor2) score 8249000 or sacrifice child
: [  367.180119] Killed process 23767 (syz-executor2) total-vm:70472kB, anon-rss:104kB, file-rss:32768kB, shmem-rss:0kB
: [  367.192101] oom_reaper: reaped process 23767 (syz-executor2), now anon-rss:0kB, file-rss:32000kB, shmem-rss:0kB
: [  367.202986] ------------[ cut here ]------------
: [  367.207845] Memory cgroup charge failed because of no reclaimable memory! This looks like a misconfiguration or a kernel bug.
: [  367.207965] WARNING: CPU: 1 PID: 23767 at mm/memcontrol.c:1710 try_charge+0x734/0x1680
: [  367.227540] Kernel panic - not syncing: panic_on_warn set ...

This is unexpected though. We have killed a task (23767) which is trying
to charge the memory which means it should
trigger the charge retry and that one should force the charge

        /*
         * Unlike in global OOM situations, memcg is not in a physical
         * memory shortage.  Allow dying and OOM-killed tasks to
         * bypass the last charges so that they can exit quickly and
         * free their memory.
         */
        if (unlikely(tsk_is_oom_victim(current) ||
                     fatal_signal_pending(current) ||
                     current->flags & PF_EXITING))
                goto force;

There doesn't seem to be any other sign of OOM killer invocation which
could then indeed lead to the warning as there is no other task to kill
(both syz-executor[23] have been killed and oom_reaped already). So I
would be curious what happened between 367.180119 which was the last
successful oom invocation and 367.207845. An additional printk in
mem_cgroup_out_of_memory might tell us more.

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 4603ad75c9a9..852cd3dbdcd9 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c

@@ -1388,6 +1388,8 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
        bool ret;

        mutex_lock(&oom_lock);
+       pr_info("task=%s pid=%d invoked memcg oom killer. oom_victim=%d\n",
+                       current->comm, current->pid, tsk_is_oom_victim(current));
        ret = out_of_memory(&oc);
        mutex_unlock(&oom_lock);
        return ret;

Anyway your memcg setup is indeed misconfigured. Memcg with 0 hard limit
and basically no memory charged by existing tasks is not going to fly
and the warning is exactly to call that out.