Re: vmalloc() in interrupt context

[Jeff Garzik]

Amit Dror wrote:
> 
> Hi,
> 
> I have a kernel driver that needs to dynamically allocate large amounts of
> memory in interrupt context.
> 
> I can't use kmalloc(GFP_ATOMIC) or get_free_pages(GFP_ATOMIC) since they are
> limited to 131056 bytes.

vmalloc won't give you a whole lot more than that in practice.  Write
some test code and see how much memory you can grab, outside of
interrupt context.

> Is there any other way to work around this problem ?

Use __vmalloc, that lets you provide a priority.  Requires 2.4.x though,
doesn't exist in 2.2.x.

Though be aware that the sort of operation you propose has a high
probability of failure even with vmalloc.  Unless you control the
hardware in this case, I would suggest considering some sort of
alternate implementation.  There is always the hack of specifying
"mem=XX" on the kernel cmd line, where XX is a value less than the total
amount of system RAM.  Then your driver can happily scribble all over
that space[1].

	Jeff

[1] unless another framegrabber or 3D driver is doing so..

-- 
Jeff Garzik              |
Building 1024            | Free beer tomorrow.
MandrakeSoft, Inc.       |