linux-kernel - Re: [PATCH 12/13 v3] ring-buffer: Add cached pages when freeing reader page

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Message-ID: <1273885618.27703.3168.camel@gandalf.stny.rr.com>
Date:	Fri, 14 May 2010 21:06:58 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 12/13 v3] ring-buffer: Add cached pages when freeing
 reader page

[ Added Peter Zijlsta since he had an interest in this topic ]

On Fri, 2010-05-14 at 18:26 -0400, Mathieu Desnoyers wrote:
> * Steven Rostedt (rostedt@...dmis.org) wrote:

> Trying to understand the effect of splice() putting the page in the page
> cache and how it affects this patch.
> 
> Basically, how do you know you can call free_page() from splice() in the
> first place ? Answering this question will probably help us see if this
> page reuse is OK.

Actually, looking at the code, I'm not sure this is safe. I was thinking
that free_page() would always free the page. But I forgot that pages
have a ref count. And a get_page() will prevent a page from freeing.

So I need to revert this patch, or rather, make a core-5 that removes
this patch and fixes the spelling in the comment.

I can later add something that checks the page ref count, but that can
wait till .36.

-- Steve




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