linux-kernel - Re: [PATCH] x86: Construct 32 bit boot time page tables in native format.

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Message-ID: <47939363.8040603@kolumbus.fi>
Date:	Sun, 20 Jan 2008 20:30:59 +0200
From:	Mika Penttilä <mika.penttila@...umbus.fi>
To:	Ian Campbell <ijc@...lion.org.uk>
CC:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH] x86: Construct 32 bit boot time page tables in native
 format.


> + * This is how much memory *in addition to the memory covered up to
> + * and including _end* we need mapped initially.  We need one bit for
> + * each possible page, but only in low memory, which means
> + * 2^32/4096/8 = 128K worst case (4G/4G split.)
> + *
> + * Modulo rounding, each megabyte assigned here requires a kilobyte of
> + * memory, which is currently unreclaimed.
> + *
> + * This should be a multiple of a page.
> + */
> +#define INIT_MAP_BEYOND_END	(128*1024)
> +
> +/*
>   

You have dropped the requirement to map all of low memory (the boot 
allocator is used for instance to construct physical mem mapping). 
Either you should fix your INIT_MAP_BEYOND_END or make a big comment 
telling us why it isn't necessary anymore to map low mem.

--Mika
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