Re: [discuss] Re: 32-bit dma allocations on 64-bit platforms

[Nick Piggin]

Andrea Arcangeli wrote:

> why does it fail? note that with the lower_zone_reserve_ratio algorithm I
> added to 2.4 all dma zone will be reserved for __GFP_DMA allocations so
> you should have troubles only with 2.6, 2.4 should work fine.
>
> So with latest 2.4 it has to fail only if you already allocated 16M with
> pci_alloc_consistent which sounds unlikely.
>
> the fact 2.6 lacks the lower_zone_reserve_ratio algorithm is a different
> issue, but I'm confortable there's no other possible algorithm to solve
> this memory balancing problem completely so there's no way around a
> forward port.
>
> well 2.6 has a tiny hack like some older 2.4 that attempts to do what
> lower_zone_reserve_ratio does, but it's not nearly enough, there's no
> per-zone-point-of-view watermark in 2.6 etc.. 2.6 actually has a more
> hardcoded hack for highmem, but the lower_zone_reserve_ratio has
> absolutely nothing to do with highmem vs lowmem. it's by pure
> coincidence that it avoids highmem machine to lockup without swap, but
> the very same problem happens on x86-64 with lowmem vs dma.

2.6 has the "incremental min" thing. What is wrong with that?
Though I think it is turned off by default.
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