[Intel-gfx] [RFC PATCH 125/162] drm/i915/lmem: Limit block size to 4G

[Chris Wilson]

Quoting Matthew Auld (2020-11-27 12:06:41)
> From: Venkata Sandeep Dhanalakota <venkata.s.dhanalakota at intel.com>
> 
> when allocating pages to lmem object of size 4G or greater
> we allocate memory blocks from buddy system.

Any lmem object is from the buddy system.

> In this scenario
> buddy sytem can allocate blocks that can have size >= 4G and
> these blocks require >32b to represent block size with these
> blocks we run into an issue with sg list construction because
> sg->length field is only 32b wide.

Just say the when using scatterlist, the maximum segment size is 4G. In
fact, we can ask sg what the backend maximum is, and use that as our max
order.

The only question is whether this merits a flag, or we just assume that
the buddy allocator is only used for objects and so always presented via
sg?
-Chris