Here is a glossary of terms used in FastMalloc. Sometimes, more than one term is used for the same thing.

'''sizeclass | class'''
{{{
number from [1, kNumClasses] identifying a size grouping
0 sizeclass means large allocation
objects of the same sizeclass:
    have the same true allocation size
    are in the same free list
}}}

'''classindex'''
{{{
location of 'size' in the sizeclass array
classindex values are cached to avoid repeat math
}}}


'''span | descriptor'''
{{{
metadata for a contiguous run of pages
either a single large allocation or
parceled into bytesize(sizeclass) units
maintains a free list for those units
maintains a total reference count for those units
}}}


'''pagemap'''
{{{
[pageID => span] mapping for all pageIDs in the address space
more than one pageID can map to the same span
}}}


'''page'''
{{{
kPageSize chunk of memory
}}}


'''pageID'''
{{{
number from [0, kNumPages] identifying a page
pageID * kPageSize = address of page
}}}

'''object'''
{{{
item in a free list
}}}

'''split (verb)'''
{{{
break a span into two parts (used by memalign)
}}}

'''carve (verb)'''
{{{
allocate a span, possibly splitting it (used by pageheap allocation functions)
}}}

'''pageheap'''
{{{
central span and page allocator
requires locking
maintains the pagemap
keeps free spanlists for spans
}}}

'''spanlist'''
{{{
2 linked lists of spans:
    mmaped (vm live)
    madvised (vm dead)
}}}

'''threadcache | heap | threadheap'''
{{{
per-thread free lists for various size classes
}}}

'''central_cache'''
{{{
central list for size classes
one lock per list
all normal-sized allocation originates in the central_cache (but may be cached in a threadcache)
}}}