linux-kernel - Re: [RFC][PATCHv6 00/12] printk: introduce printing kernel thread

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Message-ID: <20180109174750.2551c2a1@vmware.local.home>
Date:   Tue, 9 Jan 2018 17:47:50 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Jan Kara <jack@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Pavel Machek <pavel@....cz>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [RFC][PATCHv6 00/12] printk: introduce printing kernel thread

On Tue, 9 Jan 2018 14:17:05 -0800
Tejun Heo <tj@...nel.org> wrote:

> Hello, Steven.
> 
> On Tue, Jan 09, 2018 at 05:08:47PM -0500, Steven Rostedt wrote:
> > The scenario you listed would affect multiple CPUs and multiple CPUs
> > would be flooding printk. In that case my patch WILL help. Because the
> > current method, the first CPU to do the printk will get stuck doing the
> > printk for ALL OTHER CPUs. With my patch, the printk load will migrate
> > around and there will not be a single CPU that is stuck.  
> 
> Maybe it can break out eventually but that can take a really long
> time.  It's OOM.  Most of userland is waiting for reclaim.  There
> isn't all that much going on outside that and there can only be one
> CPU which is OOMing.  The kernel isn't gonna be all that chatty.

Are you saying that the OOM is stuck printing over and over on a single
CPU. Perhaps we should fix THAT.

-- Steve