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

Jesse Barnes
2006-09-22T20:41:44Z

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