linux-kernel - Re: [PATCH] [8/13] Enable the mask allocator for x86

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Date:	Fri, 7 Mar 2008 22:35:35 -0800
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Christoph Lameter" <clameter@....com>
Cc:	"Andi Kleen" <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] [8/13] Enable the mask allocator for x86

On Fri, Mar 7, 2008 at 6:37 PM, Christoph Lameter <clameter@....com> wrote:
> On Fri, 7 Mar 2008, Andi Kleen wrote:
>
>  > - Disable old ZONE_DMA
>  > No fixed size ZONE_DMA now anymore. All existing users of __GFP_DMA rely
>  > on the compat call to the maskable allocator in alloc/free_pages
>  > - Call maskable allocator initialization functions at boot
>  > - Add TRAD_DMA_MASK for the compat functions
>  > - Remove dma_reserve call
>
>  This looks okay for the disabling part. But note that there are various
>  uses of MAX_DMA_ADDRESS (sparsemem, bootmem allocator) that are currently
>  suboptimal because they set a boundary at 16MB for allocation of
>  potentially large operating system structures. That boundary continues to
>  exist despite the removal of ZONE_DMA?
>
>  It would be better to remove ZONE_DMA32 instead and enlarge ZONE_DMA so
>  that it can take over the role of ZONE_DMA. Set the boundary for
>  MAX_DMA_ADDRESS to the boundary for ZONE_DMA32. Then the
>  allocations for sparse and bootmem will be allocated above 4GB which
>  leaves lots of the lower space available for 32 bit DMA capable devices.

good. i like the idea...

How about system with only 4G or less?

YH
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