Messages in this thread | | | Date | Tue, 19 Dec 2006 10:44:31 +0100 | From | Thomas Hellström <> | Subject | Re: [patch 1/2] agpgart - allow user-populated memory types. |
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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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