linux-kernel - Re: sparsemem usage

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Message-Id: <1154532280.23655.23.camel@localhost.localdomain>
Date:	Wed, 02 Aug 2006 16:24:40 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	moreau francis <francis_moreau2000@...oo.fr>
Cc:	linux-kernel@...r.kernel.org, apw@...dowen.org
Subject: Re: sparsemem usage

Ar Mer, 2006-08-02 am 13:44 +0000, ysgrifennodd moreau francis:
> #if (MAX_ORDER - 1 + PAGE_SHIFT) > SECTION_SIZE_BITS
> #error Allocator MAX_ORDER exceeds SECTION_SIZE
> #endif
> 
> I'm not sure to understand why there's such check. To fix this
> I should change MAX_ORDER to 6.
> 
> Is it the only way to fix that ?

The kernel allocates memory out using groups of blocks in a buddy
system. 128K is smaller than one of the blocks so the kernel cannot
handle this. You need 2MB (if I remember right) granularity for your
sections but nothing stops you marking most of the 2Mb section except
the 128K that exists as "in use"

Alan

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