1fe66852ff
since `up` and `values` are both pointer-aligned the type field will
also be pointer-aligned, wasting 48 bits of space on most machines. we
can get away with removing the type field altogether by encoding some
information into the `with` expr that created the env to begin with,
reducing the GC load for the absolutely massive amount of single-entry
envs we create for lambdas. this reduces memory usage of system eval by
quite a bit (reducing heap size of our system eval from 8.4GB to 8.23GB)
and gives similar savings in eval time.
running `nix eval --raw --impure --expr 'with import <nixpkgs/nixos> {}; system'`
before:
Time (mean ± σ): 5.576 s ± 0.003 s [User: 5.197 s, System: 0.378 s]
Range (min … max): 5.572 s … 5.581 s 10 runs
after:
Time (mean ± σ): 5.408 s ± 0.002 s [User: 5.019 s, System: 0.388 s]
Range (min … max): 5.405 s … 5.411 s 10 runs
133 lines
3.3 KiB
C++
133 lines
3.3 KiB
C++
#pragma once
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///@file
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#include "eval.hh"
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namespace nix {
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/**
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* Note: Various places expect the allocated memory to be zeroed.
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*/
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[[gnu::always_inline]]
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inline void * allocBytes(size_t n)
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{
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void * p;
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#if HAVE_BOEHMGC
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p = GC_MALLOC(n);
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#else
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p = calloc(n, 1);
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#endif
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if (!p) throw std::bad_alloc();
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return p;
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}
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[[gnu::always_inline]]
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Value * EvalState::allocValue()
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{
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#if HAVE_BOEHMGC
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/* We use the boehm batch allocator to speed up allocations of Values (of which there are many).
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GC_malloc_many returns a linked list of objects of the given size, where the first word
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of each object is also the pointer to the next object in the list. This also means that we
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have to explicitly clear the first word of every object we take. */
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if (!*valueAllocCache) {
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*valueAllocCache = GC_malloc_many(sizeof(Value));
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if (!*valueAllocCache) throw std::bad_alloc();
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}
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/* GC_NEXT is a convenience macro for accessing the first word of an object.
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Take the first list item, advance the list to the next item, and clear the next pointer. */
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void * p = *valueAllocCache;
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*valueAllocCache = GC_NEXT(p);
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GC_NEXT(p) = nullptr;
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#else
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void * p = allocBytes(sizeof(Value));
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#endif
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nrValues++;
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return (Value *) p;
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}
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[[gnu::always_inline]]
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Env & EvalState::allocEnv(size_t size)
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{
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nrEnvs++;
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nrValuesInEnvs += size;
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Env * env;
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#if HAVE_BOEHMGC
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if (size == 1) {
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/* see allocValue for explanations. */
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if (!*env1AllocCache) {
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*env1AllocCache = GC_malloc_many(sizeof(Env) + sizeof(Value *));
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if (!*env1AllocCache) throw std::bad_alloc();
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}
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void * p = *env1AllocCache;
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*env1AllocCache = GC_NEXT(p);
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GC_NEXT(p) = nullptr;
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env = (Env *) p;
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} else
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#endif
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env = (Env *) allocBytes(sizeof(Env) + size * sizeof(Value *));
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/* We assume that env->values has been cleared by the allocator; maybeThunk() and lookupVar fromWith expect this. */
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return *env;
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}
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[[gnu::always_inline]]
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void EvalState::forceValue(Value & v, const PosIdx pos)
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{
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if (v.isThunk()) {
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Env * env = v.thunk.env;
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Expr * expr = v.thunk.expr;
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try {
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v.mkBlackhole();
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//checkInterrupt();
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expr->eval(*this, *env, v);
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} catch (...) {
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v.mkThunk(env, expr);
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tryFixupBlackHolePos(v, pos);
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throw;
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}
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}
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else if (v.isApp())
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callFunction(*v.app.left, *v.app.right, v, pos);
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}
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[[gnu::always_inline]]
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inline void EvalState::forceAttrs(Value & v, const PosIdx pos, std::string_view errorCtx)
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{
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forceAttrs(v, [&]() { return pos; }, errorCtx);
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}
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template <typename Callable>
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[[gnu::always_inline]]
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inline void EvalState::forceAttrs(Value & v, Callable getPos, std::string_view errorCtx)
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{
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PosIdx pos = getPos();
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forceValue(v, pos);
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if (v.type() != nAttrs) {
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error("value is %1% while a set was expected", showType(v)).withTrace(pos, errorCtx).debugThrow<TypeError>();
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}
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}
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[[gnu::always_inline]]
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inline void EvalState::forceList(Value & v, const PosIdx pos, std::string_view errorCtx)
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{
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forceValue(v, pos);
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if (!v.isList()) {
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error("value is %1% while a list was expected", showType(v)).withTrace(pos, errorCtx).debugThrow<TypeError>();
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}
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}
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}
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