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    SubjectRe: [PATCH v2 RESEND 4/7] swiotlb: Dynamically allocated bounce buffers
    On Wed, 17 May 2023 08:35:10 +0200
    Petr Tesařík <petr@tesarici.cz> wrote:

    >[...]
    > Anyway, my greatest objection to allocating additional swiotlb chunks is
    > that _all_ of them must be searched to determine that the physical
    > address does _not_ belong to a swiotlb, incurring performance penalty

    I thought about this part again, and I overlooked one option. We can
    track only the _active_ swiotlbs for each device. If a device never
    needs a swiotlb, there is no active swiotlb, and is_swiotlb_buffer()
    short-circuits to false. This should avoid all collateral damage to
    innocent devices.

    We would also maintain a (global) list of all allocated swiotlbs, used
    by swiotlb_map() to find free slots and add the respective swiotlb to
    the per-device active list.

    One potential advantage is that we could use mapping size and alignment
    to choose a swiotlb cleverly and minimize internal fragmentation...

    OK, I'm dreaming. Let's agree on the general approach first.

    Petr T

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