linux-kernel - Re: [PATCH] ring_bufer: fix BUF_PAGE

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Date:	Mon, 22 Dec 2008 12:57:28 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Lai Jiangshan <laijs@...fujitsu.com>
cc:	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ring_bufer: fix BUF_PAGE_SIZE


On Sat, 20 Dec 2008, Lai Jiangshan wrote:

> Ingo Molnar wrote:
> > * Lai Jiangshan <laijs@...fujitsu.com> wrote:
> > 
> >> impact: make BUF_PAGE_SIZE changeable.
> >>
> >> Except allocating/freeing page and the code using PAGE_MASK,
> >> all code expect buffer_page's length is BUF_PAGE_SIZE.
> >>
> >> This patch make this behavior more concordant.
> >>
> [...]
> > 
> > hm, why? Non-order-0 allocations are pretty evil - why would we ever want 
> > to do them?
> > 
> > 	Ingo
> > 
> 
> I think since we introduce BUF_PAGE_SIZE instead of PAGE_SIZE for
> buffer_page, we should make it changeable. We can use Non-order-0
> allocations, but it doesn't mean we have to use Non-order-0 allocations.
> 
> In the old codes, these lines confuse me:
> return (addr & ~PAGE_MASK) - (PAGE_SIZE - BUF_PAGE_SIZE);
> addr &= PAGE_MASK;
> This patch mostly make the codes concordant.

I need to rename the BUF_PAGE_SIZE to BUF_SIZE, since it is not really a 
page. I'm moving to keep a header on each page so that I can use splice 
and still be able to process the pages elsewhere. The BUF_SIZE is the size 
of the PAGE - that header.

I think it is too early to move the ringbuffer to bigger than a page sub 
buffers.

-- Steve

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