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From:   Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Date:   Wed, 10 Oct 2018 20:48:33 +0900
To:     Michal Hocko <mhocko@kernel.org>
Cc:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        syzbot <syzbot+77e6b28a7a7106ad0def@syzkaller.appspotmail.com>,
        hannes@cmpxchg.org, akpm@linux-foundation.org, guro@fb.com,
        kirill.shutemov@linux.intel.com, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, rientjes@google.com,
        syzkaller-bugs@googlegroups.com, yang.s@alibaba-inc.com,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Petr Mladek <pmladek@suse.com>
Subject: Re: INFO: rcu detected stall in shmem_fault
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On (10/10/18 13:35), Michal Hocko wrote:
> > Just flooding out of memory messages can trigger RCU stall problems.
> > For example, a severe skbuff_head_cache or kmalloc-512 leak bug is causing
> 
> [...]
> 
> Quite some of them, indeed! I guess we want to rate limit the output.
> What about the following?

A bit unrelated, but while we are at it:

  I like it when we rate-limit printk-s that lookup the system.
But it seems that default rate-limit values are not always good enough,
DEFAULT_RATELIMIT_INTERVAL / DEFAULT_RATELIMIT_BURST can still be too
verbose. For instance, when we have a very slow IPMI emulated serial
console -- e.g. baud rate at 57600. DEFAULT_RATELIMIT_INTERVAL and
DEFAULT_RATELIMIT_BURST can add new OOM headers and backtraces faster
than we evict them.

Does it sound reasonable enough to use larger than default rate-limits
for printk-s in OOM print-outs? OOM reports tend to be somewhat large
and the reported numbers are not always *very* unique.

What do you think?

	-ss