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further updates to documentation

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daan 2020-09-24 10:33:33 -07:00
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doc/mimalloc-doc.h
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@ -26,17 +26,25 @@ without code changes, for example, on Unix you can use it as:
Notable aspects of the design include:
- __small and consistent__: the library is less than 6k LOC using simple and
- __small and consistent__: the library is about 8k LOC using simple and
consistent data structures. This makes it very suitable
to integrate and adapt in other projects. For runtime systems it
provides hooks for a monotonic _heartbeat_ and deferred freeing (for
bounded worst-case times with reference counting).
- __free list sharding__: the big idea: instead of one big free list (per size class) we have
many smaller lists per memory "page" which both reduces fragmentation
and increases locality --
- __free list sharding__: instead of one big free list (per size class) we have
many smaller lists per "mimalloc page" which reduces fragmentation and
increases locality --
things that are allocated close in time get allocated close in memory.
(A memory "page" in _mimalloc_ contains blocks of one size class and is
usually 64KiB on a 64-bit system).
(A mimalloc page contains blocks of one size class and is usually 64KiB on a 64-bit system).
- __free list multi-sharding__: the big idea! Not only do we shard the free list
per mimalloc page, but for each page we have multiple free lists. In particular, there
is one list for thread-local `free` operations, and another one for concurrent `free`
operations. Free-ing from another thread can now be a single CAS without needing
sophisticated coordination between threads. Since there will be
thousands of separate free lists, contention is naturally distributed over the heap,
and the chance of contending on a single location will be low -- this is quite
similar to randomized algorithms like skip lists where adding
a random oracle removes the need for a more complex algorithm.
- __eager page reset__: when a "page" becomes empty (with increased chance
due to free list sharding) the memory is marked to the OS as unused ("reset" or "purged")
reducing (real) memory pressure and fragmentation, especially in long running
@ -51,7 +59,7 @@ Notable aspects of the design include:
times (_wcat_), bounded space overhead (~0.2% meta-data, with at most 12.5% waste in allocation sizes),
and has no internal points of contention using only atomic operations.
- __fast__: In our benchmarks (see [below](#performance)),
_mimalloc_ always outperforms all other leading allocators (_jemalloc_, _tcmalloc_, _Hoard_, etc),
_mimalloc_ outperforms all other leading allocators (_jemalloc_, _tcmalloc_, _Hoard_, etc),
and usually uses less memory (up to 25% more in the worst case). A nice property
is that it does consistently well over a wide range of benchmarks.