Re: Short question about the mmap method

From: Steffen Persvold (
Date: Fri Jan 04 2002 - 22:59:29 EST

Steffen Persvold wrote:
> Another thing, when allocating memory with vmalloc, how can I be sure that the pages I get is
> adressable within 4GB (i.e I wan't to call pci_map_sg on this buffer for my 32bit PCI device without
> having to use bounce buffers ) ? On systems with less that 4GB of physical memory there's no
> problem, but what happens if you have more (lets say an IA64 server with 16GB of RAM) and don't have
> an IOMMU (like alpha and sparc) ?
> I noticed a vmalloc_32 in linux/vmalloc.h (the comment says "32bit PA addressable pages - eg for PCI
> 32bit devices"), but is that one platform independent (I see that it is only using GFP_KERNEL, while
> vmalloc is using GFP_KERNEL | __GFP_HIGHMEM) ? This issue goes for __get_free_pages too I guess.

Hmm, it helps looking back at old threads (which I actually was involved in).

What ever happened to Jens Axboe's "zone_dma32" patch ? Why wasn't it included in the main 2.4.6
kernel tree (seemed like a good idea to me) ?


  Steffen Persvold   | Scalable Linux Systems |   Try out the world's best  |  | performing MPI implementation:
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