linux-kernel - Re: [PATCH V2 1/2] ftrace: Make saved_cmdlines use seq

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Message-ID: <20140529230828.4d10eb3d@gandalf.local.home>
Date:	Thu, 29 May 2014 23:08:28 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com>
Cc:	Namhyung Kim <namhyung@...nel.org>, linux-kernel@...r.kernel.org,
	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Ingo Molnar <mingo@...hat.com>, yrl.pp-manager.tt@...achi.com
Subject: Re: [PATCH V2 1/2] ftrace: Make saved_cmdlines use seq_read

On Thu, 20 Feb 2014 17:44:31 +0900
Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com> wrote:

> Current tracing_saved_cmdlines_read() implementation is naive;
> simply allocate a big buffer, construct output data on the
> buffer for each read operation, and then copy a portion of
> the buffer to the user space buffer.  This can cause a couple of
> issues such as a slow memory allocation, high cpu usage, and a
> corruption of the output data.
> 
> To address these issues, make saved_cmdlines use seq_read.

I changed the subject and change log to the following. The patch is
untouched:

    tracing: Have saved_cmdlines use the seq_read infrastructure
    
    Current tracing_saved_cmdlines_read() implementation is naive; It
    allocates a large buffer, constructs output data to that buffer for
    each read operation, and then copies a portion of the buffer to the
    user space buffer. This has several issues such as slow memory
    allocation, high CPU usage, and even corruption of the output data.
    
    The seq_read infrastructure is made to handle this type of work.
    By converting it to use seq_read() the code becomes smaller,
    simplified, as well as correct.


-- Steve
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