linux-kernel - Re: [PATCH] remove PAGE_SIZE from headers

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Date:	Sat, 14 Jul 2007 20:19:47 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Albert Cahalan <acahalan@...il.com>
CC:	olaf@...fle.de, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] remove PAGE_SIZE from headers_install

Albert Cahalan wrote:
> 
> A real constant-value PAGE_SIZE is useful and doable.
> 
> It's useful because a getpagesize() can't be used for numerous
> things, such as setting the size of an array.
> 
> It's doable, even on architectures that support multiple page
> sizes, because ABIs specify alignment requirements. There are
> two alignments of interest here:
> 
> a. the smallest that mmap() will ever naturally return on any
>   correct implementation of the architecture's ABI ("naturally"
>   meaning that MAP_FIXED was not used)
> 
> b. the smallest that mprotect() will tolerate on all
>   correct implementations of the architecture
> 
> Pick either to be the Linux definition of PAGE_SIZE.
> 

If you specify it to be one of these, people will mis-use it for the
other.  This is a bad idea.

	-hpa
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