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
next prev parent reply other threads:[~2018-11-06 14:35 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-02 13:31 [PATCH v6 1/3] printk: Add line-buffered printk() API 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
2018-11-06 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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