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From: John Ogness <john.ogness@linutronix.de>
To: Petr Mladek <pmladek@suse.com>
Cc: Andrea Parri <parri.andrea@gmail.com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
	Paul McKenney <paulmck@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	kexec@lists.infradead.org, linux-kernel@vger.kernel.org,
	Steven Rostedt <rostedt@goodmis.org>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: syslog size unread: was: [PATCH v3 3/3] printk: use the lockless ringbuffer
Date: Mon, 29 Jun 2020 23:51:40 +0200	[thread overview]
Message-ID: <87k0zp8rrn.fsf@jogness.linutronix.de> (raw)
In-Reply-To: <20200625152042.GI8444@alley> (Petr Mladek's message of "Thu, 25 Jun 2020 17:20:42 +0200")

On 2020-06-25, Petr Mladek <pmladek@suse.com> wrote:
> On Thu 2020-06-18 16:55:19, John Ogness wrote:
>> --- a/kernel/printk/printk.c
>> +++ b/kernel/printk/printk.c
>> @@ -1609,11 +1633,15 @@ int do_syslog(int type, char __user *buf, int len, int source)
>>  		break;
>>  	/* Number of chars in the log buffer */
>>  	case SYSLOG_ACTION_SIZE_UNREAD:
>> +		if (source != SYSLOG_FROM_PROC) {
>> +			text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
>> +			if (!text)
>> +				return -ENOMEM;
>
> The buffer is needed only to count lines to count the size of added
> prefixes. Could we use the new prb_read_valid_info() that allows to
> get the number of lines without actually reading the buffer?

Yes!

For the next version I introduce a macro to iterate just the meta data:

#define prb_for_each_info(from, rb, s, i, lc) \
for ((s) = from; prb_read_valid_info(rb, s, i, lc); (s) = (i)->seq + 1)

This can be used in all 3 locations where prb_count_lines() is used. In
all three places, there is no need to be copying the data. And for
SYSLOG_ACTION_SIZE_UNREAD, there is no need for the record and kmalloc'd
buffer.

This also means that prb_count_lines() will become a private static
helper of the ringbuffer.

John Ogness

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  reply	other threads:[~2020-06-29 21:51 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-18 14:49 [PATCH v3 0/3] printk: replace ringbuffer John Ogness
2020-06-18 14:49 ` [PATCH v3 1/3] crash: add VMCOREINFO macro to define offset in a struct declared by typedef John Ogness
2020-06-24  8:49   ` Petr Mladek
2020-07-04  9:30   ` Baoquan He
2020-06-18 14:49 ` [PATCH v3 2/3] printk: add lockless ringbuffer John Ogness
2020-06-29 15:32   ` Paul E. McKenney
2020-07-02  8:35   ` Petr Mladek
2020-06-18 14:49 ` [PATCH v3 3/3] printk: use the " John Ogness
2020-06-18 18:23   ` kernel test robot
2020-06-18 18:23   ` [RFC PATCH] printk: _printk_rb_static_dict can be static kernel test robot
2020-06-19  6:49     ` John Ogness
2020-06-19 12:29       ` Steven Rostedt
2020-06-25  8:16   ` truncate dict: was: Re: [PATCH v3 3/3] printk: use the lockless ringbuffer Petr Mladek
2020-06-26 13:48     ` John Ogness
2020-06-25  8:28   ` buffer allocation: was: " Petr Mladek
2020-06-26 15:02     ` John Ogness
2020-06-29 14:04       ` Petr Mladek
2020-06-29 21:57         ` John Ogness
2020-07-02 13:27           ` Petr Mladek
2020-06-25 12:09   ` record_printk_text tricks: " Petr Mladek
2020-06-25 15:25     ` Petr Mladek
2020-06-26 23:25     ` John Ogness
2020-06-25 15:17   ` pending output optimization: " Petr Mladek
2020-07-01 19:58     ` John Ogness
2020-06-25 15:20   ` syslog size unread: " Petr Mladek
2020-06-29 21:51     ` John Ogness [this message]
2020-07-02  8:25   ` lijiang
2020-07-02  9:02     ` John Ogness
2020-07-02  9:43       ` lijiang
2020-07-02 13:31         ` Petr Mladek
2020-07-04  1:12           ` lijiang
2020-07-03 11:54         ` John Ogness
2020-07-08  5:50           ` lijiang
2020-06-25  7:19 ` [PATCH v3 0/3] printk: replace ringbuffer Dave Young
2020-06-25 14:13   ` John Ogness

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