Memory descriptors for DEVICE_PRIVATE memory

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" summary

Proposal to remove struct pages for DEVICE_PRIVATE/ZONE_DEVICE memory and replace PFNs with an index into a preallocated descriptor array accessed via a soft-leaf swap entry lookup. Claims: eliminates PFN-to-page special cases, cuts huge struct page allocation time (an 80 GB init took ~30s), and avoids stealing direct-map physical address space that breaks ARM64. Recent tooling: support for 2MB THP merged and refcount fixes. Expect smaller per-object metadata, single-mapping-only descriptors, and dynamic folios or plain descriptors instead of real struct pages.

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" chapters (7)

1. 0:00Introduction to device private memory
2. 2:31Progress and ref counting fixes
3. 3:36Physical address space limitations
4. 5:25Redesigning page metadata structure
5. 8:14Eliminating PFN dependencies
6. 10:20Exploring memory descriptors
7. 14:20Summary and future directions