Arjan van de Ven wrote:
On Sat, 2006-12-09 at 00:05 +0100, Thomas Hellström wrote:
On Fri, 2006-12-08 at 19:24 +0100, Thomas Hellström wrote:
+ }
+
+ if (alloc_size <= PAGE_SIZE) {
+ new->memory = kmalloc(alloc_size, GFP_KERNEL);
+ }
+ if (new->memory == NULL) {
+ new->memory = vmalloc(alloc_size);
this bit is more or less evil as well...
1) vmalloc is expensive all the way, higher tlb use etc etc
2) mixing allocation types is just a recipe for disaster
3) if this isn't a frequent operation, kmalloc is fine upto at least 2
pages; I doubt you'll ever want more
I understand your feelings about this, and as you probably understand, the
kfree / vfree thingy is a result of the above allocation scheme.
the kfree/vfree thing at MINIMUM should be changed though. Even if you
need both kfree and vfree, you should key it off of a flag that you
store, not off the address of the memory, that's just unportable and
highly fragile. You *know* which allocator you used, so store it and use
THAT info.
The allocated memory holds an array of struct page pointers. The number of
struct page pointers will range from 1 to about 8192, so the alloc size
will range from 4bytes to 64K, but could go higher depending on
architecture.
hmm 64Kb is a bit much indeed. You can't do an array of upto 16 entries
with one page in each array entry?
Arjan,
Thanks for taking time to review this.
A short background:
The current code uses vmalloc only. The potential use of kmalloc was
introduced
to save memory and cpu-speed.
All agp drivers expect to see a single memory chunk, so I'm not sure we
want to have an array of pages. That may require rewriting a lot of code.
If it's acceptable I'd like to go for the vmalloc / kmalloc flag, or at
worst keep the current vmalloc only but that's such a _huge_ memory
waste for small buffers. The flag was the original idea, but
unfortunately the agp_memory struct is part of the drm interface, and I
wasn't sure we could add a variable to it.
DaveJ, is it possible to extend struct agp_memory with a flags field?
Regards,
Thomas
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