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Add memoise primop

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'builtins.memoise f x' is equal to 'f x', but uses a cache to speed up
repeated invocations of 'f' with the same 'x'. A typical application
is memoising evaluations of Nixpkgs in NixOps network
specifications. For example, with the patch below, the time to
evaluate a 10-machine NixOps network is reduced from 17.1s to 9.6s,
while memory consumption goes from 4486 MiB to 3089 MiB. (This is with
GC_INITIAL_HEAP_SIZE=16G.)

Nixpkgs patch:

diff --git a/pkgs/top-level/impure.nix b/pkgs/top-level/impure.nix
index a9f21e45aed..f641067e022 100644
--- a/pkgs/top-level/impure.nix
+++ b/pkgs/top-level/impure.nix
@@ -79,7 +79,7 @@ in
 # not be passed.
 assert args ? localSystem -> !(args ? system || args ? platform);

-import ./. (builtins.removeAttrs args [ "system" "platform" ] // {
+builtins.memoise or (x: x) (import ./.) (builtins.removeAttrs args [ "system" "platform" ] // {
   inherit config overlays crossSystem;
   # Fallback: Assume we are building packages on the current (build, in GNU
   # Autotools parlance) system.
This commit is contained in:
Eelco Dolstra 2018-01-11 19:24:22 +01:00
parent 435ccc7980
commit 0395b9b94a
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3 changed files with 116 additions and 1 deletions
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2
src/libexpr/eval.cc
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@ -1683,6 +1683,8 @@ void EvalState::printStats()
printMsg(v, format(" number of primop calls: %1%") % nrPrimOpCalls);
printMsg(v, format(" number of function calls: %1%") % nrFunctionCalls);
printMsg(v, format(" total allocations: %1% bytes") % (bEnvs + bLists + bValues + bAttrsets));
printMsg(v, format(" memoisation hits: %d") % nrMemoiseHits);
printMsg(v, format(" memoisation misses: %d") % nrMemoiseMisses);
#if HAVE_BOEHMGC
GC_word heapSize, totalBytes;