linux-kernel - How to alloc highmem page below 4GB on i386?

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Message-ID: <20080630200323.2a5992cd@mjolnir.drzeus.cx>
Date:	Mon, 30 Jun 2008 20:03:23 +0200
From:	Pierre Ossman <drzeus-list@...eus.cx>
To:	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: How to alloc highmem page below 4GB on i386?

Simple question. How do I allocate a page from highmem, that's still
within 32 bits? x86_64 has the DMA32 zone, but i386 has just HIGHMEM.
As most devices can't DMA above 32 bit, I have 3 GB of memory that's
not getting decent usage (or results in needless bouncing). What to do?

I tried just enabling CONFIG_DMA32 for i386, but there is some guard
against too many memory zones. I'm assuming this is there for a good
reason?

-- 
     -- Pierre Ossman

  Linux kernel, MMC maintainer        http://www.kernel.org
  rdesktop, core developer          http://www.rdesktop.org

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