• Obtain Device Tree Blob from boot loader

• Detection and Initialisation via DTB
• Poll mode & Interrupt mode
• Kernel initialisation logs must goto this device
  • Basically this should provide println! support inside kernel

Goals

• Serve as allocator for small objects in kernel.
• Best case O(1) and Worst Case O(log n) on both alloc and free operation
• Should provide Box/Rc/Arc implementation.
• Usable by any Node based container.
• Provide default set of size classes for General purpose usage
• Support Custom Size classes for critical types.

Design

• Default set of size classes are determined at build time
• Each size class represents the object size and the page size from which each object is carved
• Two strategies are supported.
  • Always choose a partially filled page with most amount of free blocks
    • Best for overall performance.
    • Subsequent allocations returns nearby blocks - Improves cache usage
    • SlabPool cache hit also increased due to using the same metadata over multiple allocations.
  • Always choose a partially filled page with least amount of free blocks.
    • Overall Memory Efficient.
    • Best for avoiding fragmentation (External)
    • Facilitates earlier release of free'd block to upstream allocator.
  • But once a page is choosen, it will be used until all its free blocks are exhausted.
• 5 Levels (Watermarks) - used to approximate sorted blocks.
  • 5 levels after - fully empty (no free blocks) pages.
  • Atleast 1 free block to 20 % blocks free.
  • 20 - 40 % blocks free.
  • 40 - 60 % blocks free.
  • 60 - 80 % blocks free.
  • 80 - 100 % blocks free.
• Metadata is stored externally outside the page to
  • Allow full utilization of page
  • Security purposes - memory corruption possibly won't corrupt Slab Metadata.
• After mounting the kernel image, rest (Majority) of RAM is provided to SLAB manager
• Memory for SLAB metadata is reserved and rest of the address range is provided to Buddy Allocator.
• Empty pages are obtained from Buddy Allocator and it is also exposed outside as General Purpose page allocator.
• Custom size classes are supported via RegisterSizeClass API.
  • Only the object size needs to be provided. Page size is automatically chosen.

Design Tasks

• Determine API for SLAB initialization
• Determine API Custom Size class Registration
• Determine General purpose size classes and their page sizes
• Determine object size to size class mapper
• How to minimize Unsafe usage?

• Device tree is loaded in compile time via feature flag.

• Detection and Initialisation via DTB
• Poll mode & Interrupt mode

• Interrupt handling
• Timer Interrupt