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Date: Tue, 30 Sep 2008 13:41:23 -0400 (EDT)
From: Steven Rostedt <rostedt@goodmis.org>
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To: Peter Zijlstra <peterz@infradead.org>
cc: Linus Torvalds <torvalds@linux-foundation.org>,
       Jonathan Corbet <corbet@lwn.net>,
       Mathieu Desnoyers <compudj@krystal.dyndns.org>,
       LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>,
       Thomas Gleixner <tglx@linutronix.de>,
       Andrew Morton <akpm@linux-foundation.org>, prasad@linux.vnet.ibm.com,
       "Frank Ch. Eigler" <fche@redhat.com>, David Wilder <dwilder@us.ibm.com>,
       hch@lst.de, Martin Bligh <mbligh@google.com>,
       Christoph Hellwig <hch@infradead.org>,
       Masami Hiramatsu <mhiramat@redhat.com>,
       Steven Rostedt <srostedt@redhat.com>,
       Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Subject: Re: [PATCH v10 Golden] Unified trace buffer
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On Tue, 30 Sep 2008, Peter Zijlstra wrote:
> > 
> > Actually, looking at the code, there is no reason I need to keep this in 
> > the frame buffer itself. I've also encapsulated the accesses to the 
> > incrementing of the pointers so it would be trivial to try other 
> > approaches.
> > 
> > The problem we had with the big array struct is that we can want large 
> > buffers and to do that with pointers means we would need to either come up 
> > with a large allocator or use vmap.
> > 
> > But I just realized that I could also just make a link list of page 
> > pointers and do the exact same thing without having to worry about page 
> > frames.  Again, the way I coded this up, it is quite trivial to replace 
> > the handling of the pages with other schemes.
> 
> The list_head in the page frame should be available regardless of
> splice() stuffs.

Regardless, there's more info we want to store for each page than the list 
head.  Especially when we start converting this to lockless. I rather get 
out of the overlaying of the page frames, its nice to save the space, but 
really scares the hell out of me. I can just imagine this blowing up if we 
redo the paging, and I dislike this transparent coupling between the 
tracer buffer and the pages.

-- Steve