[igt-dev] [PATCH i-g-t v14 05/33] lib/intel_allocator_simple: Add simple allocator

[Chris Wilson]

Quoting Zbigniew Kempczyński (2021-01-14 12:22:05)
> +static uint64_t get_bias(int fd)
> +{
> +       (void) fd;
> +
> +       return 256 << 10;
> +}

So I immediately ran into trouble with bias + RESERVED affecting my
ability to layout my full-ppgtt exactly as I wanted.

The kernel BATCH_BIAS only exists to prevent negative deltas from
causing invalid wraparounds [for relocations] and is not applied to
softpin, since the user is expected not to be using relocations and so
in full control. RESERVED is an interesting debate as we need to avoid
common test cases from tripping over prefetching past the last page,
while at the same time we want to allow full control to the tests that
demand it.
-Chris