Messages in this thread | | | Date | Thu, 2 Nov 2006 15:17:15 -0800 | From | Jun Sun <> | Subject | Re: Can Linux live without DMA zone? |
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On Thu, Nov 02, 2006 at 11:19:05PM +0100, Arjan van de Ven wrote: > On Thu, 2006-11-02 at 16:26 -0500, Phillip Susi wrote: > > Arjan van de Ven wrote: > > > that's for the 32 bit boundary. THe problem is that there are 31, 30, 28 > > > and 26 bit devices as well, and those are in more trouble, and will > > > eventually fall back to GFP_DMA (inside the x86 PCI code; the driver > > > just uses the pci dma allocation routines) if they can't get suitable > > > memory otherwise.... > > > > > > It's all nice in theory. But then there is the reality that not all > > > devices are nice pci device that implement the entire spec;) > > > > > > > Right, but doesn't the bounce/allocation routine take as a parameter the > > limit that the device can handle? If the device can handle 28 bit > > addresses, then the kernel should not limit it to only 24 bits. > > you're right in theory, but the kernel only has a few pools of memory > available, but not at every bit boundary. there is a 32 bit pool > (GFP_DMA32) on some, a 30-ish bit pool (GFP_KERNEL) on others, and a 24 > bit pool (GFP_DMA) with basically nothing inbetween. >
Perhaps a better solution is to
1. get rid of DMA zone
2. have another alloc funciton (e.g., kmalloc_range()) which takes an extra pair of parameters to indicate the desired range for the allocated memory. Most DMA buffers are allocated during start-up. So the alloc operations should generally be successful.
3. convert drivers over to use the new function.
Cheers.
Jun are allocated at start-up time. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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