On Mon, Mar 01, 2004 at 06:51:56PM +0100, Takashi Iwai wrote:
> a small concern about GFP_KERNEL is that i experienced the stall when
> the kernel tried to allocate large continuous pages with GFP_KERNEL,
> e.g. modprobe stops infinitely in the module init phase (and you
> cannot even interrupt that process).
>
> does dma_alloc_coherent(GFP_KERNEL) with big pages work without stall?
It depends where the stall was coming from. Do you have any further
details?
Also, on a similar note, I hope someone noticed one of the comments I
added in the second patch:
+ *
+ * Really, we want to move this type of thing into dma_alloc_coherent()
+ * so dma_mask doesn't have to be messed with.
(referring to the hack towards the top of memalloc.c.)
This is something which really needs solving more cleanly. What I
think you're trying to do is to allocate pages for devices whose
DMA mask indicates (eg) 28 bit addressing is possible, but without
the "ISA DMA" (<16MB) restriction? Could you confirm this?
If this is correct, I suspect it may be something which is not
limited to sound devices, and as such should probably be covered
by the generic code (iow, dma_alloc_coherent.) However, that's
going to require discussion with other several people.
Currently, x86 dma_alloc_coherent() is:
if (dev == NULL || (*dev->dma_mask < 0xffffffff))
gfp |= GFP_DMA;
ret = (void *)__get_free_pages(gfp, get_order(size));
if (ret != NULL) {
memset(ret, 0, size);
*dma_handle = virt_to_phys(ret);
}
return ret;
I'm thinking of something more like:
order = get_order(size);
mask = 16*1024*1024-1;
if (dev)
mask = dev->dma_mask;
while (1) {
ret = (void *)__get_free_pages(gfp, order);
if (ret == NULL || gfp & GFP_DMA)
break;
handle = virt_to_phys(ret);
if ((handle & ~mask) == 0) {
memset(ret, 0, size);
*dma_handle = handle;
break;
}
free_pages((unsigned long)ret, order);
gfp |= GFP_DMA;
}
return ret;
Does that look reasonable? If so, I'll float the idea around x86
people.
--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of: 2.6 PCMCIA - http://pcmcia.arm.linux.org.uk/
2.6 Serial core
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