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From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Petr Mladek <pmladek@suse.com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Dmitriy Vyukov <dvyukov@google.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Alexander Potapenko <glider@google.com>,
	Fengguang Wu <fengguang.wu@intel.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-mm@kvack.org, Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH v6 1/3] printk: Add line-buffered printk() API.
Date: Tue, 6 Nov 2018 23:35:02 +0900	[thread overview]
Message-ID: <20181106143502.GA32748@tigerII.localdomain> (raw)
In-Reply-To: <1541165517-3557-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>

On (11/02/18 22:31), Tetsuo Handa wrote:
>   (1) Call get_printk_buffer() and acquire "struct printk_buffer *".
> 
>   (2) Rewrite printk() calls in the following way. The "ptr" is
>       "struct printk_buffer *" obtained in step (1).
> 
>       printk(fmt, ...)     => printk_buffered(ptr, fmt, ...)
>       vprintk(fmt, args)   => vprintk_buffered(ptr, fmt, args)
>       pr_emerg(fmt, ...)   => bpr_emerg(ptr, fmt, ...)
>       pr_alert(fmt, ...)   => bpr_alert(ptr, fmt, ...)
>       pr_crit(fmt, ...)    => bpr_crit(ptr, fmt, ...)
>       pr_err(fmt, ...)     => bpr_err(ptr, fmt, ...)
>       pr_warning(fmt, ...) => bpr_warning(ptr, fmt, ...)
>       pr_warn(fmt, ...)    => bpr_warn(ptr, fmt, ...)
>       pr_notice(fmt, ...)  => bpr_notice(ptr, fmt, ...)
>       pr_info(fmt, ...)    => bpr_info(ptr, fmt, ...)
>       pr_cont(fmt, ...)    => bpr_cont(ptr, fmt, ...)
> 
>   (3) Release "struct printk_buffer" by calling put_printk_buffer().

[..]

> Since we want to remove "struct cont" eventually, we will try to remove
> both "implicit printk() users who are expecting KERN_CONT behavior" and
> "explicit pr_cont()/printk(KERN_CONT) users". Therefore, converting to
> this API is recommended.

- The printk-fallback sounds like a hint that the existing 'cont' handling
  better stay in the kernel. I don't see how the existing 'cont' is
  significantly worse than
		bpr_warn(NULL, ...)->printk() // no 'cont' support
  I don't see why would we want to do it, sorry. I don't see "it takes 16
  printk-buffers to make a thing go right" as a sure thing.

A question.

How bad would it actually be to:

- Allocate seq_buf 512-bytes buffer (GFP_ATOMIC) just-in-time, when we
  need it.
    // How often systems cannot allocate a 512-byte buffer? //

- OK, assuming that systems around the world are so badly OOM like all the
  time and even kmalloc(512) is absolutely impossible, then have a fallback
  to the existing 'cont' handling; it just looks to me better than a plain
  printk()-fallback with removed 'cont' support.

- Do not allocate seq_buf if we are in printk-safe or in printk-nmi mode.
  To avoid "buffering for the sake of buffering". IOW, when in printk-safe
  use printk-safe.

	-ss

  parent reply	other threads:[~2018-11-06 14:35 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-02 13:31 Tetsuo Handa
2018-11-02 13:31 ` [PATCH 2/3] mm: Use line-buffered printk() for show_free_areas() Tetsuo Handa
2018-11-07 14:07   ` Petr Mladek
2018-11-02 13:31 ` [PATCH 3/3] lockdep: Use line-buffered printk() for lockdep messages Tetsuo Handa
2018-11-02 13:36   ` Peter Zijlstra
2018-11-03  2:00     ` Tetsuo Handa
2018-11-06  8:38     ` Petr Mladek
2018-11-06  9:05       ` Sergey Senozhatsky
2018-11-06 12:57         ` Petr Mladek
2018-11-06  9:56       ` Tetsuo Handa
2018-11-07 15:19   ` Petr Mladek
2018-11-08  4:45     ` Sergey Senozhatsky
2018-11-08 11:37       ` Tetsuo Handa
2018-11-09  6:12         ` Sergey Senozhatsky
2018-11-09  9:55           ` Tetsuo Handa
2018-11-09 15:43             ` Petr Mladek
2018-11-10  2:42               ` Tetsuo Handa
2018-11-23 12:46                 ` Petr Mladek
2018-11-23 13:12                   ` Tetsuo Handa
2018-11-23 15:56                   ` Steven Rostedt
2018-11-24  0:24                     ` Tetsuo Handa
2018-11-26  4:34                       ` Sergey Senozhatsky
2018-11-28 13:29                     ` David Laight
2018-11-29 10:09                       ` Tetsuo Handa
2018-11-30 16:01                         ` Petr Mladek
2018-11-10  8:52               ` Tetsuo Handa
2018-11-23 12:52                 ` Petr Mladek
2018-11-09 14:08           ` Linus Torvalds
2018-11-09 14:42             ` Steven Rostedt
2018-11-08 11:53       ` Petr Mladek
2018-11-08 12:44         ` Sergey Senozhatsky
2018-11-08 14:21           ` Sergey Senozhatsky
2018-11-09  9:54     ` Tetsuo Handa
2018-11-02 14:40 ` [PATCH v6 1/3] printk: Add line-buffered printk() API Matthew Wilcox
2018-11-03  1:55   ` Tetsuo Handa
2018-11-02 18:12 ` kbuild test robot
2018-11-02 18:12   ` kbuild test robot
2018-11-06 14:35 ` Sergey Senozhatsky [this message]
2018-11-07 10:21   ` Petr Mladek
2018-11-07 12:54     ` Tetsuo Handa
2018-11-08  2:21     ` Sergey Senozhatsky
2018-11-08 11:24       ` Petr Mladek
2018-11-08 11:46         ` Tetsuo Handa
2018-11-08 12:30         ` Sergey Senozhatsky
2018-11-09 14:10           ` Petr Mladek
2018-11-12  7:59             ` Sergey Senozhatsky
2018-11-12 10:42               ` Tetsuo Handa
2018-11-17 10:14               ` Tetsuo Handa
2018-11-07 10:52   ` Tetsuo Handa
2018-11-07 11:01     ` David Laight
2018-11-07 12:00       ` Petr Mladek
2018-11-07 11:45     ` Petr Mladek
2018-11-08  2:30     ` Sergey Senozhatsky
2018-11-07 13:41 ` Petr Mladek
2018-11-07 14:06 ` Petr Mladek

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