linux-kernel - Re: [rfc] no ZERO

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Date:	Wed, 4 Apr 2007 16:55:32 +0300
From:	Dan Aloni <da-x@...atomic.org>
To:	Andrea Arcangeli <andrea@...e.de>
Cc:	Nick Piggin <npiggin@...e.de>, Hugh Dickins <hugh@...itas.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	tee@....com, holt@....com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [rfc] no ZERO_PAGE?

On Wed, Apr 04, 2007 at 02:27:01PM +0200, Andrea Arcangeli wrote:
> On Wed, Apr 04, 2007 at 12:24:07PM +0200, Nick Piggin wrote:
> > But for a potential mainline merge, maybe starting with a CONFIG
> > option is a good idea -- defaulting to off, and we could start by
> > turning it on just in -rc kernels for a few releases, to get a bit
> > more confidence?
> 
> The only reason to do that is if there are many stupid apps pretending
> to get meaningful information from pages that cannot contain any
> information. The zero page in the anon page fault has been there
> forever so...

There might be a lot of applications like that, and I'm not sure that 
_all_ of them can be considered 'stupid' as you say.

How about applications that perform mmap() and R/W random-access on 
large *sparse* files? (e.g. a scientific app that uses a large sparse 
file as a big database look-up table). As I see it, these apps would
need to keep track of what's sparse and what's not...

-- 
Dan Aloni
XIV LTD, http://www.xivstorage.com
da-x (at) monatomic.org, dan (at) xiv.co.il
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