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

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Date:	Sat, 20 Dec 2008 17:31:25 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Steven Rostedt <rostedt@...dmis.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ring_bufer: fix BUF_PAGE_SIZE

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.

	Lai


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