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Enable parallel marking in boehm-gc #13708

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Merged
xokdvium merged 3 commits into from
Aug 7, 2025
Merged

Enable parallel marking in boehm-gc #13708

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a3ff648
Call GC_allow_register_threads() to enable parallel marking in Boehm GC
edolstra Aug 4, 2025
4c1c4f7
Move setting GC_THREADS into eval-gc.hh
edolstra Aug 4, 2025
0d559f0
Increase the initial Boehm GC mark stack size
edolstra Aug 4, 2025
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16 changes: 13 additions & 3 deletions packaging/dependencies.nix
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Original file line number Diff line number Diff line change
Expand Up @@ -50,9 +50,19 @@ scope: {
requiredSystemFeatures = [ ];
};

boehmgc = pkgs.boehmgc.override {
enableLargeConfig = true;
};
boehmgc =
(pkgs.boehmgc.override {
enableLargeConfig = true;
}).overrideAttrs
(attrs: {
# Increase the initial mark stack size to avoid stack
# overflows, since these inhibit parallel marking (see
# GC_mark_some()). To check whether the mark stack is too
# small, run Nix with GC_PRINT_STATS=1 and look for messages
# such as `Mark stack overflow`, `No room to copy back mark
# stack`, and `Grew mark stack to ... frames`.
NIX_CFLAGS_COMPILE = "-DINITIAL_MARK_STACK_SIZE=1048576";
});

# TODO Hack until https://github.com/NixOS/nixpkgs/issues/45462 is fixed.
boost =
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5 changes: 3 additions & 2 deletions src/libexpr/eval-gc.cc
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Expand Up @@ -15,8 +15,6 @@
# include <pthread_np.h>
# endif

# include <gc/gc.h>
# include <gc/gc_cpp.h>
# include <gc/gc_allocator.h>

# include <boost/coroutine2/coroutine.hpp>
Expand Down Expand Up @@ -53,6 +51,9 @@ static inline void initGCReal()

GC_INIT();

/* Enable parallel marking. */
GC_allow_register_threads();

/* Register valid displacements in case we are using alignment niches
for storing the type information. This way tagged pointers are considered
to be valid, even when they are not aligned. */
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3 changes: 2 additions & 1 deletion src/libexpr/include/nix/expr/eval-gc.hh
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Expand Up @@ -3,12 +3,13 @@

#include <cstddef>

// For `NIX_USE_BOEHMGC`, and if that's set, `GC_THREADS`
// For `NIX_USE_BOEHMGC`
#include "nix/expr/config.hh"

#if NIX_USE_BOEHMGC

# define GC_INCLUDE_NEW
# define GC_THREADS 1

# include <gc/gc.h>
# include <gc/gc_cpp.h>
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3 changes: 0 additions & 3 deletions src/libexpr/include/nix/expr/eval-inline.hh
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Expand Up @@ -6,9 +6,6 @@
#include "nix/expr/eval-error.hh"
#include "nix/expr/eval-settings.hh"

// For `NIX_USE_BOEHMGC`, and if that's set, `GC_THREADS`
#include "nix/expr/config.hh"

namespace nix {

/**
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2 changes: 0 additions & 2 deletions src/libexpr/meson.build
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Expand Up @@ -61,8 +61,6 @@ if bdw_gc.found()
define_value = cxx.has_function(funcspec).to_int()
configdata_priv.set(define_name, define_value)
endforeach
# Affects ABI, because it changes what bdw_gc itself does!
configdata_pub.set('GC_THREADS', 1)
endif
# Used in public header. Affects ABI!
configdata_pub.set('NIX_USE_BOEHMGC', bdw_gc.found().to_int())
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