Messages in this thread | | | Date | Wed, 8 Nov 2023 11:52:07 +0100 | From | Halil Pasic <> | Subject | Re: Memory corruption with CONFIG_SWIOTLB_DYNAMIC=y |
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On Fri, 3 Nov 2023 19:59:49 +0100 Petr Tesařík <petr@tesarici.cz> wrote:
> > Not sure how to properly fix this as the different alignment > > requirements get pretty complex quickly. So would appreciate your > > input. > > I don't think it's possible to improve the allocation logic without > modifying the page allocator and/or the DMA atomic pool allocator to > take additional constraints into account.
I don't understand. What speaks against calculating the amount of space needed, so that with the waste we can still fit the bounce-buffer in the pool?
I believe alloc_size + combined_mask is a trivial upper bound, but we can do slightly better since we know that we allocate pages.
For the sake of simplicity let us assume we only have the min_align_mask requirement. Then I believe the worst case is that we need (orig_addr & min_align_mask & PAGE_MASK) + (min_align_mask & ~PAGE_MASK) extra space to fit.
Depending on how the semantics pan out one may be able to replace min_align_mask with combined_mask.
Is your point that for large combined_mask values _get_free_pages(GFP_NOWAIT | __GFP_NOWARN, required_order) is not likely to complete successfully?
Regards, Halil
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