51e75bca89
The memcpy implementation is not completely stupid but is almost certainly not as good as a carefully tuned and optimised one. Building snmalloc with FreeBSD's libc memcpy + jemalloc and with this, each 10 times, does not show a statistically significant performance difference at 95% confidence. The snmalloc version has very slightly lower median and worst-case times. This is in no way a sensible benchmark, but it serves as a smoke test for significant performance regressions. The CI self-host job now uses the checked memcpy. This also fixes an off-by-one error in the external bounds. This is triggered by ninja, so we will see breakage in CI if it is reintroduced. In debug builds, we provide a verbose error containing the address of the allocation, the base and bounds of the allocation, and a backtrace. The backtrace was broken by the CI cleanup moving the BACKTRACE_HEADER macro into the SNMALLOC_ namespace. This is also fixed. The test involves hijacking `abort`, which doesn't work everywhere. It also requires `backtrace` to work in configurations where stack traces are enabled. This is disabled in QEMU because `backtrace` appears to crash reliably in QEMU user mode. For now, in the -checks build configurations, we are hitting a slow path in the pagemap on accesses so that the pages that are `PROT_NONE` don't cause crashes. These need to be made read-only, but this requires a PAL change.
648 lines
21 KiB
C++
648 lines
21 KiB
C++
#pragma once
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#ifdef _MSC_VER
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# define ALLOCATOR __declspec(allocator)
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#else
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# define ALLOCATOR
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#endif
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#include "../ds/ptrwrap.h"
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#include "corealloc.h"
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#include "freelist.h"
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#include "localcache.h"
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#include "pool.h"
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#include "remotecache.h"
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#include "sizeclasstable.h"
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#ifdef SNMALLOC_PASS_THROUGH
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# include "external_alloc.h"
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#endif
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#ifdef SNMALLOC_TRACING
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# include <iostream>
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#endif
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#include <string.h>
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#include <utility>
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namespace snmalloc
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{
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enum Boundary
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{
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/**
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* The location of the first byte of this allocation.
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*/
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Start,
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/**
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* The location of the last byte of the allocation.
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*/
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End,
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/**
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* The location one past the end of the allocation. This is mostly useful
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* for bounds checking, where anything less than this value is safe.
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*/
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OnePastEnd
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};
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/**
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* A local allocator contains the fast-path allocation routines and
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* encapsulates all of the behaviour of an allocator that is local to some
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* context, typically a thread. This delegates to a `CoreAllocator` for all
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* slow-path operations, including anything that requires claiming new chunks
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* of address space.
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*
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* The template parameter defines the configuration of this allocator and is
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* passed through to the associated `CoreAllocator`. The `Options` structure
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* of this defines one property that directly affects the behaviour of the
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* local allocator: `LocalAllocSupportsLazyInit`, which defaults to true,
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* defines whether the local allocator supports lazy initialisation. If this
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* is true then the local allocator will construct a core allocator the first
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* time it needs to perform a slow-path operation. If this is false then the
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* core allocator must be provided externally by invoking the `init` method
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* on this class *before* any allocation-related methods are called.
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*/
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template<SNMALLOC_CONCEPT(ConceptBackendGlobals) SharedStateHandle>
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class LocalAllocator
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{
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public:
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using StateHandle = SharedStateHandle;
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private:
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using CoreAlloc = CoreAllocator<SharedStateHandle>;
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// Free list per small size class. These are used for
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// allocation on the fast path. This part of the code is inspired by
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// mimalloc.
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// Also contains remote deallocation cache.
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LocalCache local_cache{&SharedStateHandle::unused_remote};
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// Underlying allocator for most non-fast path operations.
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CoreAlloc* core_alloc{nullptr};
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// As allocation and deallocation can occur during thread teardown
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// we need to record if we are already in that state as we will not
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// receive another teardown call, so each operation needs to release
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// the underlying data structures after the call.
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bool post_teardown{false};
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/**
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* Checks if the core allocator has been initialised, and runs the
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* `action` with the arguments, args.
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*
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* If the core allocator is not initialised, then first initialise it,
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* and then perform the action using the core allocator.
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*
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* This is an abstraction of the common pattern of check initialisation,
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* and then performing the operations. It is carefully crafted to tail
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* call the continuations, and thus generate good code for the fast path.
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*/
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template<typename Action, typename... Args>
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SNMALLOC_FAST_PATH decltype(auto) check_init(Action action, Args... args)
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{
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if (likely(core_alloc != nullptr))
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{
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return core_alloc->handle_message_queue(action, core_alloc, args...);
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}
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return lazy_init(action, args...);
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}
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/**
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* This initialises the fast allocator by acquiring a core allocator, and
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* setting up its local copy of data structures.
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*
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* If the allocator does not support lazy initialisation then this assumes
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* that initialisation has already taken place and invokes the action
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* immediately.
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*/
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template<typename Action, typename... Args>
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SNMALLOC_SLOW_PATH decltype(auto) lazy_init(Action action, Args... args)
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{
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SNMALLOC_ASSERT(core_alloc == nullptr);
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if constexpr (!SharedStateHandle::Options.LocalAllocSupportsLazyInit)
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{
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SNMALLOC_CHECK(
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false &&
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"lazy_init called on an allocator that doesn't support lazy "
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"initialisation");
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// Unreachable, but needed to keep the type checker happy in deducing
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// the return type of this function.
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return static_cast<decltype(action(core_alloc, args...))>(nullptr);
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}
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else
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{
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// Initialise the thread local allocator
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if constexpr (SharedStateHandle::Options.CoreAllocOwnsLocalState)
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{
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init();
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}
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// register_clean_up must be called after init. register clean up may
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// be implemented with allocation, so need to ensure we have a valid
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// allocator at this point.
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if (!post_teardown)
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// Must be called at least once per thread.
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// A pthread implementation only calls the thread destruction handle
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// if the key has been set.
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SharedStateHandle::register_clean_up();
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// Perform underlying operation
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auto r = action(core_alloc, args...);
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// After performing underlying operation, in the case of teardown
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// already having begun, we must flush any state we just acquired.
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if (post_teardown)
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{
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#ifdef SNMALLOC_TRACING
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std::cout << "post_teardown flush()" << std::endl;
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#endif
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// We didn't have an allocator because the thread is being torndown.
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// We need to return any local state, so we don't leak it.
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flush();
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}
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return r;
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}
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}
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/**
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* Allocation that are larger than are handled by the fast allocator must be
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* passed to the core allocator.
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*/
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template<ZeroMem zero_mem>
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SNMALLOC_SLOW_PATH void* alloc_not_small(size_t size)
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{
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if (size == 0)
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{
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// Deal with alloc zero of with a small object here.
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// Alternative semantics giving nullptr is also allowed by the
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// standard.
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return small_alloc<NoZero>(1);
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}
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return check_init([&](CoreAlloc* core_alloc) {
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// Grab slab of correct size
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// Set remote as large allocator remote.
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auto [chunk, meta] = ChunkAllocator::alloc_chunk<SharedStateHandle>(
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core_alloc->get_backend_local_state(),
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bits::next_pow2_bits(size), // TODO
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large_size_to_chunk_sizeclass(size),
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large_size_to_chunk_size(size),
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SharedStateHandle::fake_large_remote);
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// set up meta data so sizeclass is correct, and hence alloc size, and
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// external pointer.
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#ifdef SNMALLOC_TRACING
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std::cout << "size " << size << " pow2 size "
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<< bits::next_pow2_bits(size) << std::endl;
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#endif
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// Note that meta data is not currently used for large allocs.
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// meta->initialise(size_to_sizeclass(size));
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UNUSED(meta);
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if (zero_mem == YesZero)
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{
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SharedStateHandle::Pal::template zero<false>(
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chunk.unsafe_ptr(), size);
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}
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return chunk.unsafe_ptr();
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});
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}
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template<ZeroMem zero_mem>
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SNMALLOC_FAST_PATH void* small_alloc(size_t size)
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{
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// SNMALLOC_ASSUME(size <= sizeclass_to_size(NUM_SIZECLASSES));
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auto slowpath = [&](
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sizeclass_t sizeclass,
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FreeListIter* fl) SNMALLOC_FAST_PATH_LAMBDA {
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if (likely(core_alloc != nullptr))
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{
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return core_alloc->handle_message_queue(
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[](CoreAlloc* core_alloc, sizeclass_t sizeclass, FreeListIter* fl) {
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return core_alloc->template small_alloc<zero_mem>(sizeclass, *fl);
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},
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core_alloc,
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sizeclass,
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fl);
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}
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return lazy_init(
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[&](CoreAlloc*, sizeclass_t sizeclass) {
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return small_alloc<zero_mem>(sizeclass_to_size(sizeclass));
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},
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sizeclass);
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};
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return local_cache.template alloc<zero_mem, SharedStateHandle>(
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size, slowpath);
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}
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/**
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* Send all remote deallocation to other threads.
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*/
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void post_remote_cache()
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{
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core_alloc->post();
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}
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/**
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* Slow path for deallocation we do not have space for this remote
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* deallocation. This could be because,
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* - we actually don't have space for this remote deallocation,
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* and need to send them on; or
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* - the allocator was not already initialised.
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* In the second case we need to recheck if this is a remote deallocation,
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* as we might acquire the originating allocator.
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*/
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SNMALLOC_SLOW_PATH void dealloc_remote_slow(void* p)
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{
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if (core_alloc != nullptr)
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{
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#ifdef SNMALLOC_TRACING
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std::cout << "Remote dealloc post" << p << " size " << alloc_size(p)
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<< std::endl;
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#endif
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MetaEntry entry = SharedStateHandle::Pagemap::get_metaentry(
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core_alloc->backend_state_ptr(), address_cast(p));
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local_cache.remote_dealloc_cache.template dealloc<sizeof(CoreAlloc)>(
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entry.get_remote()->trunc_id(), CapPtr<void, CBAlloc>(p), key_global);
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post_remote_cache();
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return;
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}
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// Recheck what kind of dealloc we should do incase, the allocator we get
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// from lazy_init is the originating allocator.
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lazy_init(
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[&](CoreAlloc*, void* p) {
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dealloc(p); // TODO don't double count statistics
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return nullptr;
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},
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p);
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}
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/**
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* Abstracts access to the message queue to handle different
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* layout configurations of the allocator.
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*/
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auto& message_queue()
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{
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return local_cache.remote_allocator;
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}
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/**
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* Call `SharedStateHandle::is_initialised()` if it is implemented,
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* unconditionally returns true otherwise.
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*/
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SNMALLOC_FAST_PATH
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bool is_initialised()
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{
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return call_is_initialised<SharedStateHandle>(nullptr, 0);
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}
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/**
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* SFINAE helper. Matched only if `T` implements `ensure_init`. Calls it
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* if it exists.
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*/
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template<typename T>
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SNMALLOC_FAST_PATH auto call_ensure_init(T*, int)
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-> decltype(T::ensure_init())
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{
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T::ensure_init();
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}
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/**
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* SFINAE helper. Matched only if `T` does not implement `ensure_init`.
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* Does nothing if called.
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*/
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template<typename T>
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SNMALLOC_FAST_PATH auto call_ensure_init(T*, long)
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{}
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/**
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* Call `SharedStateHandle::ensure_init()` if it is implemented, do nothing
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* otherwise.
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*/
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SNMALLOC_FAST_PATH
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void ensure_init()
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{
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call_ensure_init<SharedStateHandle>(nullptr, 0);
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}
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public:
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constexpr LocalAllocator() = default;
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LocalAllocator(const LocalAllocator&) = delete;
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LocalAllocator& operator=(const LocalAllocator&) = delete;
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/**
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* Initialise the allocator. For allocators that support local
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* initialisation, this is called with a core allocator that this class
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* allocates (from a pool allocator) the first time it encounters a slow
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* path. If this class is configured without lazy initialisation support
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* then this must be called externally
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*/
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void init(CoreAlloc* c)
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{
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// Initialise the global allocator structures
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ensure_init();
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// Should only be called if the allocator has not been initialised.
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SNMALLOC_ASSERT(core_alloc == nullptr);
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// Attach to it.
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c->attach(&local_cache);
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core_alloc = c;
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#ifdef SNMALLOC_TRACING
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std::cout << "init(): core_alloc=" << core_alloc << "@" << &local_cache
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<< std::endl;
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#endif
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// local_cache.stats.sta rt();
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}
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// This is effectively the constructor for the LocalAllocator, but due to
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// not wanting initialisation checks on the fast path, it is initialised
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// lazily.
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void init()
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{
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// Initialise the global allocator structures
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ensure_init();
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// Grab an allocator for this thread.
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init(AllocPool<SharedStateHandle>::acquire(&(this->local_cache)));
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}
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// Return all state in the fast allocator and release the underlying
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// core allocator. This is used during teardown to empty the thread
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// local state.
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void flush()
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{
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// Detached thread local state from allocator.
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if (core_alloc != nullptr)
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{
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core_alloc->flush();
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// core_alloc->stats().add(local_cache.stats);
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// // Reset stats, required to deal with repeated flushing.
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// new (&local_cache.stats) Stats();
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// Detach underlying allocator
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core_alloc->attached_cache = nullptr;
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// Return underlying allocator to the system.
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if constexpr (SharedStateHandle::Options.CoreAllocOwnsLocalState)
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{
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AllocPool<SharedStateHandle>::release(core_alloc);
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}
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// Set up thread local allocator to look like
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// it is new to hit slow paths.
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core_alloc = nullptr;
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#ifdef SNMALLOC_TRACING
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std::cout << "flush(): core_alloc=" << core_alloc << std::endl;
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#endif
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local_cache.remote_allocator = &SharedStateHandle::unused_remote;
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local_cache.remote_dealloc_cache.capacity = 0;
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}
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}
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/**
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* Allocate memory of a dynamically known size.
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*/
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template<ZeroMem zero_mem = NoZero>
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SNMALLOC_FAST_PATH ALLOCATOR void* alloc(size_t size)
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{
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#ifdef SNMALLOC_PASS_THROUGH
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// snmalloc guarantees a lot of alignment, so we can depend on this
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// make pass through call aligned_alloc with the alignment snmalloc
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// would guarantee.
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void* result = external_alloc::aligned_alloc(
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natural_alignment(size), round_size(size));
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if constexpr (zero_mem == YesZero)
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memset(result, 0, size);
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return result;
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#else
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// Perform the - 1 on size, so that zero wraps around and ends up on
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// slow path.
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if (likely((size - 1) <= (sizeclass_to_size(NUM_SIZECLASSES - 1) - 1)))
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{
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// Small allocations are more likely. Improve
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// branch prediction by placing this case first.
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return small_alloc<zero_mem>(size);
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}
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// TODO capptr_reveal?
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return alloc_not_small<zero_mem>(size);
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#endif
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}
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/**
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* Allocate memory of a statically known size.
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*/
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template<size_t size, ZeroMem zero_mem = NoZero>
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SNMALLOC_FAST_PATH ALLOCATOR void* alloc()
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{
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// TODO optimise
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return alloc<zero_mem>(size);
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}
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SNMALLOC_FAST_PATH void dealloc(void* p)
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{
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#ifdef SNMALLOC_PASS_THROUGH
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external_alloc::free(p);
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#else
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// TODO:
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// Care is needed so that dealloc(nullptr) works before init
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// The backend allocator must ensure that a minimal page map exists
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// before init, that maps null to a remote_deallocator that will never be
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// in thread local state.
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const MetaEntry& entry = SharedStateHandle::Pagemap::get_metaentry(
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core_alloc->backend_state_ptr(), address_cast(p));
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if (likely(local_cache.remote_allocator == entry.get_remote()))
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{
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if (likely(CoreAlloc::dealloc_local_object_fast(
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entry, p, local_cache.entropy)))
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return;
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core_alloc->dealloc_local_object_slow(entry);
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return;
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}
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if (likely(entry.get_remote() != SharedStateHandle::fake_large_remote))
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{
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// Check if we have space for the remote deallocation
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if (local_cache.remote_dealloc_cache.reserve_space(entry))
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{
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local_cache.remote_dealloc_cache.template dealloc<sizeof(CoreAlloc)>(
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entry.get_remote()->trunc_id(),
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CapPtr<void, CBAlloc>(p),
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key_global);
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# ifdef SNMALLOC_TRACING
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std::cout << "Remote dealloc fast" << p << " size " << alloc_size(p)
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<< std::endl;
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# endif
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return;
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}
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dealloc_remote_slow(p);
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return;
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}
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// Large deallocation or null.
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if (likely(p != nullptr))
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{
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// Check this is managed by this pagemap.
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check_client(entry.get_sizeclass() != 0, "Not allocated by snmalloc.");
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size_t size = bits::one_at_bit(entry.get_sizeclass());
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// Check for start of allocation.
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check_client(
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pointer_align_down(p, size) == p, "Not start of an allocation.");
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size_t slab_sizeclass = large_size_to_chunk_sizeclass(size);
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# ifdef SNMALLOC_TRACING
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std::cout << "Large deallocation: " << size
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<< " chunk sizeclass: " << slab_sizeclass << std::endl;
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# endif
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ChunkRecord* slab_record =
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reinterpret_cast<ChunkRecord*>(entry.get_metaslab());
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slab_record->chunk = CapPtr<void, CBChunk>(p);
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check_init(
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[](
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CoreAlloc* core_alloc,
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ChunkRecord* slab_record,
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size_t slab_sizeclass) {
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|
ChunkAllocator::dealloc<SharedStateHandle>(
|
|
core_alloc->get_backend_local_state(),
|
|
slab_record,
|
|
slab_sizeclass);
|
|
return nullptr;
|
|
},
|
|
slab_record,
|
|
slab_sizeclass);
|
|
return;
|
|
}
|
|
|
|
# ifdef SNMALLOC_TRACING
|
|
std::cout << "nullptr deallocation" << std::endl;
|
|
# endif
|
|
return;
|
|
#endif
|
|
}
|
|
|
|
SNMALLOC_FAST_PATH void dealloc(void* p, size_t s)
|
|
{
|
|
UNUSED(s);
|
|
dealloc(p);
|
|
}
|
|
|
|
template<size_t size>
|
|
SNMALLOC_FAST_PATH void dealloc(void* p)
|
|
{
|
|
UNUSED(size);
|
|
dealloc(p);
|
|
}
|
|
|
|
void teardown()
|
|
{
|
|
#ifdef SNMALLOC_TRACING
|
|
std::cout << "Teardown: core_alloc=" << core_alloc << "@" << &local_cache
|
|
<< std::endl;
|
|
#endif
|
|
post_teardown = true;
|
|
if (core_alloc != nullptr)
|
|
{
|
|
flush();
|
|
}
|
|
}
|
|
|
|
SNMALLOC_FAST_PATH size_t alloc_size(const void* p_raw)
|
|
{
|
|
#ifdef SNMALLOC_PASS_THROUGH
|
|
return external_alloc::malloc_usable_size(const_cast<void*>(p_raw));
|
|
#else
|
|
// Note that this should return 0 for nullptr.
|
|
// Other than nullptr, we know the system will be initialised as it must
|
|
// be called with something we have already allocated.
|
|
// To handle this case we require the uninitialised pagemap contain an
|
|
// entry for the first chunk of memory, that states it represents a large
|
|
// object, so we can pull the check for null off the fast path.
|
|
MetaEntry entry = SharedStateHandle::Pagemap::get_metaentry(
|
|
core_alloc->backend_state_ptr(), address_cast(p_raw));
|
|
|
|
if (likely(entry.get_remote() != SharedStateHandle::fake_large_remote))
|
|
return sizeclass_to_size(entry.get_sizeclass());
|
|
|
|
// Sizeclass zero is for large is actually zero
|
|
if (likely(entry.get_sizeclass() != 0))
|
|
return bits::one_at_bit(entry.get_sizeclass());
|
|
|
|
return 0;
|
|
#endif
|
|
}
|
|
|
|
/**
|
|
* Returns the Start/End of an object allocated by this allocator
|
|
*
|
|
* It is valid to pass any pointer, if the object was not allocated
|
|
* by this allocator, then it give the start and end as the whole of
|
|
* the potential pointer space.
|
|
*/
|
|
template<Boundary location = Start>
|
|
void* external_pointer(void* p_raw)
|
|
{
|
|
#ifndef SNMALLOC_PASS_THROUGH
|
|
// TODO bring back the CHERI bits. Wes to review if required.
|
|
MetaEntry entry =
|
|
SharedStateHandle::Pagemap::template get_metaentry<true>(
|
|
core_alloc->backend_state_ptr(), address_cast(p_raw));
|
|
auto sizeclass = entry.get_sizeclass();
|
|
if (likely(entry.get_remote() != SharedStateHandle::fake_large_remote))
|
|
{
|
|
auto rsize = sizeclass_to_size(sizeclass);
|
|
auto offset =
|
|
address_cast(p_raw) & (sizeclass_to_slab_size(sizeclass) - 1);
|
|
auto start_offset = round_by_sizeclass(sizeclass, offset);
|
|
if constexpr (location == Start)
|
|
{
|
|
UNUSED(rsize);
|
|
return pointer_offset(p_raw, start_offset - offset);
|
|
}
|
|
else if constexpr (location == End)
|
|
return pointer_offset(p_raw, rsize + start_offset - offset - 1);
|
|
else
|
|
return pointer_offset(p_raw, rsize + start_offset - offset);
|
|
}
|
|
|
|
// Sizeclass zero of a large allocation is used for not managed by us.
|
|
if (likely(sizeclass != 0))
|
|
{
|
|
// This is a large allocation, find start by masking.
|
|
auto rsize = bits::one_at_bit(sizeclass);
|
|
auto start = pointer_align_down(p_raw, rsize);
|
|
if constexpr (location == Start)
|
|
return start;
|
|
else if constexpr (location == End)
|
|
return pointer_offset(start, rsize - 1);
|
|
else
|
|
return pointer_offset(start, rsize);
|
|
}
|
|
#else
|
|
UNUSED(p_raw);
|
|
#endif
|
|
|
|
if constexpr ((location == End) || (location == OnePastEnd))
|
|
// We don't know the End, so return MAX_PTR
|
|
return reinterpret_cast<void*>(UINTPTR_MAX);
|
|
else
|
|
// We don't know the Start, so return MIN_PTR
|
|
return nullptr;
|
|
}
|
|
|
|
/**
|
|
* Accessor, returns the local cache. If embedding code is allocating the
|
|
* core allocator for use by this local allocator then it needs to access
|
|
* this field.
|
|
*/
|
|
LocalCache& get_local_cache()
|
|
{
|
|
return local_cache;
|
|
}
|
|
};
|
|
} // namespace snmalloc
|