Messages in this thread | | | Subject | Re: [RFC] Initial alpha-0 for new page allocator API | From | Alan Cox <> | Date | Fri, 22 Sep 2006 21:10:50 +0100 |
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Ar Gwe, 2006-09-22 am 21:10 +0200, ysgrifennodd Andi Kleen: > We already have that scheme. Any existing driver should be already converted > away from GFP_DMA towards dma_*/pci_*. dma_* knows all the magic > how to get memory for the various ranges. No need to mess up the > main allocator.
Add an isa_device class and that'll fall into place nicely. isa_alloc_* will end up asking for 20bit DMA and it will work nicely.
> Anyways, i suppose what could be added as a fallback would be a > really_slow_brute_force_try_to_get_something_in_this_range() allocator
Implementation detail although I note that the defrag/antifrag proposal made at the vm summit would mean it mostly come out for free. If we have an isa_dma_* API then the detail is platform specific.
> that basically goes through the buddy lists freeing in >O(1) > and does some directed reclaim, but that would likely be a separate > path anyways and not need your new structure to impact the O(1) > allocator.
Just search within the candidate 4MB (or whatever it is these days) chunks.
> I am still unconvinced of the real need. The only gaping hole was > GFP_DMA32, which we fixed already.
Various devices are 30 and 31bit today - some broadcom for example.
> Ok there is aacraid with its weird 2GB limit, > Ok now I'm sure someone will come up with a counter example (hi Alan), but: > - Does the device really need more than 16MB? > - How often is it used on systems with >1/2GB with a 64bit kernel? > [consider that 64bit kernels don't support ISA] > - How many users of that particular thing around?
Ok the examples I know about are - ESS Maestro series audio - PCI, common on 32bit boxes a few years ago, no longer shipped and unlikely to be met on 64bit. Also slow allocations is fine. - Some aacraid, mostly only for control structures. Those found on 64bit are probably fine with slow alloc. - Broadcom stuff - not sure if 30 or 31bit, around today and on 64bit - Floppy controller
> I think my point stands.
I think its worthy of discussion.
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