From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: mhocko@kernel.org
Cc: rostedt@goodmis.org, linux-kernel@vger.kernel.org,
akpm@linux-foundation.org, linux-mm@kvack.org,
xiyou.wangcong@gmail.com, dave.hansen@intel.com,
hannes@cmpxchg.org, mgorman@suse.de, pmladek@suse.com,
sergey.senozhatsky@gmail.com, vbabka@suse.cz,
peterz@infradead.org, torvalds@linux-foundation.org,
jack@suse.cz, mathieu.desnoyers@efficios.com,
rostedt@home.goodmis.org
Subject: Re: [PATCH v4] printk: Add console owner and waiter logic to loadbalance console writes
Date: Thu, 9 Nov 2017 21:07:15 +0900 [thread overview]
Message-ID: <201711092107.BBE78653.tQLSOOFJMFVHOF@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <20171109113156.i36uazn4esxm2vzw@dhcp22.suse.cz>
Michal Hocko wrote:
> On Thu 09-11-17 20:03:30, Tetsuo Handa wrote:
> > Michal Hocko wrote:
> > > On Thu 09-11-17 19:22:58, Tetsuo Handa wrote:
> > > > Michal Hocko wrote:
> > > > > Hi,
> > > > > assuming that this passes warn stall torturing by Tetsuo, do you think
> > > > > we can drop http://lkml.kernel.org/r/1509017339-4802-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp
> > > > > from the mmotm tree?
> > > >
> > > > I don't think so.
> > > >
> > > > The rule that "do not try to printk() faster than the kernel can write to
> > > > consoles" will remain no matter how printk() changes. Unless asynchronous
> > > > approach like https://lwn.net/Articles/723447/ is used, I think we can't
> > > > obtain useful information.
> > >
> > > Does that mean that the patch doesn't pass your test?
> > >
> >
> > Test is irrelevant. See the changelog.
> >
> > Synchronous approach is prone to unexpected results (e.g. too late [1], too
> > frequent [2], overlooked [3]). As far as I know, warn_alloc() never helped
> > with providing information other than "something is going wrong".
> > I want to consider asynchronous approach which can obtain information
> > during stalls with possibly relevant threads (e.g. the owner of oom_lock
> > and kswapd-like threads) and serve as a trigger for actions (e.g. turn
> > on/off tracepoints, ask libvirt daemon to take a memory dump of stalling
> > KVM guest for diagnostic purpose).
> >
> > [1] https://bugzilla.kernel.org/show_bug.cgi?id=192981
> > [2] http://lkml.kernel.org/r/CAM_iQpWuPVGc2ky8M-9yukECtS+zKjiDasNymX7rMcBjBFyM_A@mail.gmail.com
> > [3] commit db73ee0d46379922 ("mm, vmscan: do not loop on too_many_isolated for ever")
>
> So you want to keep the warning out of the kernel even though the
> problems you are seeing are gone just to allow for an async approach
> nobody is very fond of? That is a very dubious approach.
You are assuming that there are no more bugs which will be caught by
an async approach. That is seriously wrong. [3] is just an example.
http://lkml.kernel.org/r/CABXGCsOzaorL0wKZFYRFKR7RSnUL+7=vspE36sFTENoimsJGSw@mail.gmail.com
is an example where async approach will help. For example, turn various tracepoints on
if stall lasted for 5 seconds and then turn them off when stall disappeared.
It is very unfortunate that we still do not have such trigger.
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next prev parent reply other threads:[~2017-11-09 12:08 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-08 15:27 [PATCH v4] printk: Add console owner and waiter logic to load balance console writes Steven Rostedt
2017-11-09 10:12 ` Michal Hocko
2017-11-09 10:22 ` [PATCH v4] printk: Add console owner and waiter logic to loadbalance " Tetsuo Handa
2017-11-09 10:26 ` Michal Hocko
2017-11-09 11:03 ` Tetsuo Handa
2017-11-09 11:31 ` Michal Hocko
2017-11-09 12:07 ` Tetsuo Handa [this message]
2017-11-24 15:54 ` [PATCH v4] printk: Add console owner and waiter logic to load balance " Petr Mladek
2017-11-24 15:58 ` Petr Mladek
2017-11-27 8:53 ` Byungchul Park
2017-11-28 1:42 ` Byungchul Park
2017-12-08 14:00 ` Petr Mladek
2017-12-12 5:39 ` Sergey Senozhatsky
2017-12-12 19:27 ` Steven Rostedt
2017-12-13 1:50 ` Sergey Senozhatsky
2017-12-14 14:34 ` Petr Mladek
2017-12-14 13:51 ` Petr Mladek
2017-11-27 8:48 ` Byungchul Park
2017-11-28 6:23 ` Sergey Senozhatsky
2017-12-22 10:31 ` Petr Mladek
2017-12-22 12:44 ` Steven Rostedt
2018-01-10 12:50 ` Petr Mladek
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