diff --git a/Memory-Manager.md b/Memory-Manager.md new file mode 100644 index 0000000..35c921f --- /dev/null +++ b/Memory-Manager.md @@ -0,0 +1,43 @@ + +## User Level Functions +The main functions that a user needs are: +`gc_alloc` -- malloc with gc +`gc_free` -- free with gc + +These are built on top of a memory structure using Allocation Table Bytes (ATBs) +## Memory Structure +Memory is split up into 4 Allocation Tables. Every Allocation Table has a `ATB` which stands for "Allocation Table Byte". This is a single byte containing 4 sets of the following +``` +// 0b00 = FREE -- free block +// 0b01 = HEAD -- head of a chain of blocks +// 0b10 = TAIL -- in the tail of a chain of blocks +// 0b11 = MARK -- marked head block +``` +These are known as `ATB_0` through `ATB_3` and have several C methods (i.e. functions and macros) to access their attributes. These include: + +BLOCKS_PER_ATB -- The number of ATB's that fit in an Allocation Table +ATB_MASK_0 -- Get the relevant bytes for ATB_0 +... +ATB_MASK_3 + +ATB_0_IS_FREE(a) -- Determine whether table is currently free +... +ATB_3_IS_FREE(a) + +**What do these do? Why are they useful???** +BLOCK_SHIFT(block) +ATB_GET_KIND(block) +ATB_ANY_TO_FREE(block) +ATB_FREE_TO_HEAD(block) +ATB_FREE_TO_TAIL(block) +ATB_HEAD_TO_MARK(block) +ATB_MARK_TO_HEAD(block) + +BLOCK_FROM_PTR(ptr) +PTR_FROM_BLOCK(block) +ATB_FROM_BLOCK(bl) + +## Questions +- Is there documentation for the above methods? I think that would help me understand what they do +- How is the memory structured? How is it gotten? Does python take out an array of data, or does it take out single elements at at time? I am having trouble understanding how this memory manager is supposed to be used. +- How many pointers can the memory manager handle at once (on your reference implementation, I believe 128k of memory)? Does the size of the data being requested matter? How does it deal with fragmentation? For instance, if the system asks for a few 100byte arrays and a few 5byte structs one after another, and then frees the 100byte arrays -- how does it handle the fragmentation? Is there a memory defragmenter?