linux-kernel - Re: remove zero_page (was Re: -mm merge plans for 2.6.24)

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Date:	Tue, 9 Oct 2007 07:52:39 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Nick Piggin <nickpiggin@...oo.com.au>
cc:	Hugh Dickins <hugh@...itas.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: remove zero_page (was Re: -mm merge plans for 2.6.24)



On Tue, 9 Oct 2007, Nick Piggin wrote:
> 
> I have done some tests which indicate a couple of very basic common tools
> don't do much zero-page activity (ie. kbuild). And also combined with some
> logical arguments to say that a "sane" app wouldn't be using zero_page much.
> (basically -- if the app cares about memory or cache footprint and is using
> many pages of zeroes, then it should have a more compressed representation
> of zeroes anyway).

One of the things that zero-page has been used for is absolutely *huge* 
(but sparse) arrays in Fortan programs.

At least in traditional fortran, it was very hard to do dynamic 
allocations, so people would allocate the *maximum* array statically, and 
then not necessarily use everything. I don't know if the pages ever even 
got paged in, but this is the kind of usage which is *not* insane.

		Linus
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