[$] Slab allocator: sheaves and any-context allocations

The kernel's slab allocator is charged with providing small objects ondemand; its performance and reliability are crucial for the functioning ofthe system as a whole. At the 2025 Linux Storage, Filesystem,Memory-Management, and BPF Summit, two adjacent sessions in thememory-management track dug into current work on the slab allocator. Thefirst focused on the new sheaves feature, while the second discussed a setof allocation functions that are safe to call in any context.