linux-kernel - Re: [RFC] Initial alpha-0 for new page allocator API

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Date:	Fri, 22 Sep 2006 13:41:44 -0700
From:	Jesse Barnes <jesse.barnes@...el.com>
To:	Christoph Lameter <clameter@....com>
Cc:	Martin Bligh <mbligh@...igh.org>, Andi Kleen <ak@...e.de>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, akpm@...gle.com,
	linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	James Bottomley <James.Bottomley@...eleye.com>,
	linux-mm@...ck.org
Subject: Re: [RFC] Initial alpha-0 for new page allocator API

On Friday, September 22, 2006 1:23 pm, Christoph Lameter wrote:
> Here is an iniitial patch of alloc_pages_range (untested, compiles).
> Directed reclaim missing. Feedback wanted. There are some comments in
> the patch where I am at the boundary of my knowledge and it would be
> good if someone could supply the info needed.
>
> Index: linux-2.6.18-rc7-mm1/arch/i386/kernel/pci-dma.c
> ===================================================================
> --- linux-2.6.18-rc7-mm1.orig/arch/i386/kernel/pci-dma.c	2006-09-22
> 15:10:42.246731179 -0500 +++
> linux-2.6.18-rc7-mm1/arch/i386/kernel/pci-dma.c	2006-09-22
> 15:11:10.449709078 -0500 @@ -26,6 +26,8 @@ void
> *dma_alloc_coherent(struct device *
>  			   dma_addr_t *dma_handle, gfp_t gfp)
>  {
>  	void *ret;
> +	unsigned long low = 0L;
> +	unsigned long high = 0xffffffff;
>  	struct dma_coherent_mem *mem = dev ? dev->dma_mem : NULL;
>  	int order = get_order(size);
>  	/* ignore region specifiers */
> @@ -44,10 +46,14 @@ void *dma_alloc_coherent(struct device *
>  			return NULL;
>  	}
>
> -	if (dev == NULL || (dev->coherent_dma_mask < 0xffffffff))
> -		gfp |= GFP_DMA;
> +	if (dev == NULL)
> +		/* Apply safe ISA LIMITS */
> +		high = 16*1024*1024L;
> +	else
> +	if (dev->coherent_dma_mask < 0xffffffff)
> +		high = dev->coherent_dma_mask;

With your alloc_pages_range this check can go away.  I think only the dev 
== NULL check is needed with this scheme since it looks like there's no 
way (currently) for ISA devices to store their masks for later 
consultation by arch code? 

> +	/*
> +	 * Is there an upper/lower limit of installed memory that we could
> +	 * check against instead of -1 ? The less memory installed the less
> +	 * the chance that we would have to do the expensive range search.
> +	 */
> +	if (high == -1L && low == 0L)
> +		return alloc_pages(gfp_flags, order);

There's max_pfn, but on machines with large memory holes using it might not 
help much.

Jesse
-
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