linux-kernel - Re: [patch] cache pipe buf page address for non-highmem arch

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Message-ID: <20070324014024.GL17334@kvack.org>
Date:	Fri, 23 Mar 2007 21:40:24 -0400
From:	Benjamin LaHaise <bcrl@...ck.org>
To:	Christoph Hellwig <hch@...radead.org>,
	Ken Chen <kenchen@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] cache pipe buf page address for non-highmem arch

On Fri, Mar 23, 2007 at 10:14:52AM +0000, Christoph Hellwig wrote:
> I think you're fixing the symptom here and not the cause.  If calculating
> the virtual address of a page is so expensive on your setup it should
> define WANT_PAGE_VIRTUAL and we should always cache the virtual address
> in struct page.  There's a lot more code, epecially in filesystems that's
> rather upset about a slow page_address.

Andi shot that down when I brought it up a while ago, as it does show 
up in profiles for networking and other code paths.  His argument is that 
the loss of memory is excessive.  Personally, I think the benefits of a 
64 byte struct page on x86-64 outweigh the memory loss, as it means page 
index to address translations are a simple shift.

		-ben
-- 
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