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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@rostedt.homelinux.com
Subject: Re: [PATCH v4] printk: Add console owner and waiter logic to loadbalance console writes
Date: Thu, 9 Nov 2017 20:03:30 +0900	[thread overview]
Message-ID: <201711092003.ACJ86411.FOFtFMVOJOSLHQ@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <20171109102613.hp6waybyxbkb3crz@dhcp22.suse.cz>

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")

WARNING: multiple messages have this Message-ID (diff)
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 20:03:30 +0900	[thread overview]
Message-ID: <201711092003.ACJ86411.FOFtFMVOJOSLHQ@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <20171109102613.hp6waybyxbkb3crz@dhcp22.suse.cz>

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")

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  reply	other threads:[~2017-11-09 11:03 UTC|newest]

Thread overview: 44+ 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
2017-11-08 15:27 ` Steven Rostedt
2017-11-09 10:12 ` Michal Hocko
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 10:22     ` Tetsuo Handa
2017-11-09 10:26     ` Michal Hocko
2017-11-09 10:26       ` Michal Hocko
2017-11-09 11:03       ` Tetsuo Handa [this message]
2017-11-09 11:03         ` Tetsuo Handa
2017-11-09 11:31         ` Michal Hocko
2017-11-09 11:31           ` Michal Hocko
2017-11-09 12:07           ` Tetsuo Handa
2017-11-09 12:07             ` Tetsuo Handa
2017-11-24 15:54 ` [PATCH v4] printk: Add console owner and waiter logic to load balance " Petr Mladek
2017-11-24 15:54   ` Petr Mladek
2017-11-24 15:58   ` Petr Mladek
2017-11-24 15:58     ` Petr Mladek
2017-11-27  8:53     ` Byungchul Park
2017-11-27  8:53       ` Byungchul Park
2017-11-28  1:42     ` Byungchul Park
2017-11-28  1:42       ` Byungchul Park
2017-12-08 14:00       ` Petr Mladek
2017-12-08 14:00         ` Petr Mladek
2017-12-12  5:39         ` Sergey Senozhatsky
2017-12-12  5:39           ` Sergey Senozhatsky
2017-12-12 19:27           ` Steven Rostedt
2017-12-12 19:27             ` Steven Rostedt
2017-12-13  1:50             ` Sergey Senozhatsky
2017-12-13  1:50               ` Sergey Senozhatsky
2017-12-14 14:34             ` Petr Mladek
2017-12-14 14:34               ` Petr Mladek
2017-12-14 13:51     ` Petr Mladek
2017-12-14 13:51       ` Petr Mladek
2017-11-27  8:48 ` Byungchul Park
2017-11-27  8:48   ` Byungchul Park
2017-11-28  6:23   ` Sergey Senozhatsky
2017-11-28  6:23     ` Sergey Senozhatsky
2017-12-22 10:31 ` Petr Mladek
2017-12-22 10:31   ` Petr Mladek
2017-12-22 12:44   ` Steven Rostedt
2017-12-22 12:44     ` Steven Rostedt
2018-01-10 12:50     ` Petr Mladek
2018-01-10 12:50       ` Petr Mladek

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