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WIP: BatchIt (#677)

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* Rename dealloc_local_object_slower to _meta

Unlike its brethren, `dealloc_local_object` and
`dealloc_local_object_slow`, the `dealloc_local_object_slower` method
does not take a pointer to free space.  Make this slightly more apparent
by renaming it and adding some commentary to both definition and call
site.

* corealloc: get meta in dealloc_local_object

Make both _fast() and _slow() arms take the meta as an argument; _meta()
already did.

* Introduce RemoteMessage structure

Plumb its use around remoteallocator and remotecache

* NFC: Plumb metadata to remotecache dealloc

* Initial steps in batched remote messages

This prepares the recipient to process a batched message.

* Initial dealloc-side batching machinery

Exercise recipient machinery by having the senders collect adjacent frees to
the same slab into a batch.

* Match free batch keying to slab freelist keying

* freelist: add append_segment

* SlabMetadata: machinery for returning multiple objects

This might involve multiple (I think at most two, at the moment) transitions in
the slab lifecycle state machine.  Towards that end, return indicators to the
caller that the slow path must be taken and how many objects of the original
set have not yet been counted as returned.

* corealloc: operate ring-at-a-time on remote queues

* RemoteCache associative cache of rings

* RemoteCache: N-set caching

* Initial CHERI support for free rings

* Matt's fix for slow-path codegen

* Try: remotecache: don't store allocator IDs

We can, as Matt so kindly reminds me, go get them from the pagemap.  Since we
need this value only when closing a ring, the read from over there is probably
not very onerous.  (We could also get the slab pointer from an object in the
ring, but we need that whenever inserting into the cache, so it's probably more
sensible to store that locally?)

* Make BatchIt optional

Move ring set bits and associativity knobs to allocconfig and expose them via
CMake.  If associtivity is zero, use non-batched implementations of the
`RemoteMessage` and `RemoteDeallocCacheBatching` classes.

By default, kick BatchIt on when we have enough room in the minimum allocation
size to do it.  Exactly how much space is enough is a function of which
mitigations we have enabled and whether or not we are compiling with C++20.

This commit reverts the change to `MIN_ALLOC_SIZE` made in "Introduce
RemoteMessage structure" now that we have multiple types, and zies, of
remote messages to choose from.

* RemoteDeallocCacheBatching: store metas as address

There's no need for a full pointer here, it'd just make the structure larger on
CHERI.

* NFC: plumb entropy from LocalAlloc to BatchIt

* BatchIt random eviction

In order not to thwart `mitigations(random_preserve)` too much, if it's on in
combination with BatchIt, roll the dice every time we append to a batch to
decide if we should stochastically evict this batch.  By increasing the number
of batches, we allow the recipient allocator increased opportunity to randomly
stripe batches across the two `freelist::Builder` segments associated with each
slab.

---------

Co-authored-by: Nathaniel Wesley Filardo <nfilardo@microsoft.com>
Co-authored-by: Matthew Parkinson <mattpark@microsoft.com>
This commit is contained in:
Nathaniel Wesley Filardo
2024-09-23 18:18:09 +00:00
committed by GitHub
parent 416fd39f6a
commit fb776da909
9 changed files with 755 additions and 51 deletions
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5
CMakeLists.txt
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@@ -65,6 +65,9 @@ endif()
set(SNMALLOC_MIN_ALLOC_SIZE "" CACHE STRING "Minimum allocation bytes (power of 2)")
set(SNMALLOC_MIN_ALLOC_STEP_SIZE "" CACHE STRING "Minimum allocation step (power of 2)")
set(SNMALLOC_DEALLOC_BATCH_RING_ASSOC "" CACHE STRING "Associativity of deallocation batch cache; 0 to disable")
set(SNMALLOC_DEALLOC_BATCH_RING_SET_BITS "" CACHE STRING "Logarithm of number of deallocation batch cache associativity sets")
if(MSVC AND SNMALLOC_STATIC_LIBRARY AND (SNMALLOC_STATIC_LIBRARY_PREFIX STREQUAL ""))
message(FATAL_ERROR "Empty static library prefix not supported on MSVC")
endif()
@@ -251,6 +254,8 @@ if (SNMALLOC_NO_REALLOCARR)
endif()
add_as_define_value(SNMALLOC_MIN_ALLOC_SIZE)
add_as_define_value(SNMALLOC_MIN_ALLOC_STEP_SIZE)
add_as_define_value(SNMALLOC_DEALLOC_BATCH_RING_ASSOC)
add_as_define_value(SNMALLOC_DEALLOC_BATCH_RING_SET_BITS)
target_compile_definitions(snmalloc INTERFACE $<$<BOOL:CONST_QUALIFIED_MALLOC_USABLE_SIZE>:MALLOC_USABLE_SIZE_QUALIFIER=const>)