linux-kernel - Re: [PATCH] perf: fix ring_buffer perf_output

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Message-ID: <CABPqkBRGutLBC+mO+F8fH5F-Yoe1NL8e_=yF9boxA28jNLO56g@mail.gmail.com>
Date:	Mon, 18 Mar 2013 14:03:22 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>, Jiri Olsa <jolsa@...hat.com>,
	Frédéric Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH] perf: fix ring_buffer perf_output_space() boundary calculation

On Mon, Mar 18, 2013 at 1:59 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, 2013-03-18 at 13:48 +0100, Stephane Eranian wrote:
>>         if (!rb->writable)
>> -               return true;
>> +               return false;
>
>
> writable means user writable (VM_WRITE); the difference is that a
> !VM_WRITE buffer will simply over-write its own tail whereas a VM_WRITE
> buffer will drop events.
>
> So returning true for !VM_WRITE makes sense, there's always space.
>
Ok, that was not so clear to me. I think this if() statment deserves a comment.
I will add that in V2.
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