From 16d93cfd9fa8f5a61f0650d6749b4fcd7353bb86 Mon Sep 17 00:00:00 2001
From: Amaan Qureshi <git@amaanq.com>
Date: Mon, 9 Mar 2026 23:06:57 -0400
Subject: [PATCH 1/2] jemalloc: default to 64KB page size on ppc64

Most ppc64 kernels default to 64KB pages, for example, Fedora, SUSE,
Arch POWER, and the upstream kernel itself (for Book3S, i.e. POWER4+)
all ship with `CONFIG_PPC_64K_PAGES=y`, however, NixOS forces 4KB
pages via `PPC_4K_PAGES`. A higher `--with-lg-page` is
forward-compatible with lower page sizes but may waste some memory, so
this commit trades a small amount of memory for broader build-host
compatibility.
---
 pkgs/by-name/je/jemalloc/package.nix | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/pkgs/by-name/je/jemalloc/package.nix b/pkgs/by-name/je/jemalloc/package.nix
index 202195c152db..389cec8ca60c 100644
--- a/pkgs/by-name/je/jemalloc/package.nix
+++ b/pkgs/by-name/je/jemalloc/package.nix
@@ -55,7 +55,11 @@ stdenv.mkDerivation (finalAttrs: {
   # https://sources.debian.org/src/jemalloc/5.3.0-3/debian/rules/
   ++ [
     (
-      if (stdenv.hostPlatform.isAarch64 || stdenv.hostPlatform.isLoongArch64) then
+      if
+        (
+          stdenv.hostPlatform.isAarch64 || stdenv.hostPlatform.isLoongArch64 || stdenv.hostPlatform.isPower64
+        )
+      then
         "--with-lg-page=16"
       else
         "--with-lg-page=12"

From e29eca25fc5c51f34a9af75c83a8f37a677522a7 Mon Sep 17 00:00:00 2001
From: Amaan Qureshi <git@amaanq.com>
Date: Tue, 10 Mar 2026 02:07:47 -0400
Subject: [PATCH 2/2] jemalloc: add overridable `pageSizeKiB` argument

This commit exposes the page size as an overridable `pageSizeKiB` argument
instead of hardcoding the lg-page logic inline. This lets users tune
jemalloc for their specific kernel page size via an overlay, e.g.
`jemalloc.override { pageSizeKiB = 4; }` for 4KB-page kernels on a platform
that ordinarily would have 64KB pages.
---
 pkgs/by-name/je/jemalloc/package.nix | 34 ++++++++++++++++++++--------
 1 file changed, 24 insertions(+), 10 deletions(-)

diff --git a/pkgs/by-name/je/jemalloc/package.nix b/pkgs/by-name/je/jemalloc/package.nix
index 389cec8ca60c..0871ff1d4d61 100644
--- a/pkgs/by-name/je/jemalloc/package.nix
+++ b/pkgs/by-name/je/jemalloc/package.nix
@@ -13,8 +13,31 @@
   # compatibility.
   stripPrefix ? stdenv.hostPlatform.isDarwin,
   disableInitExecTls ? false,
+  # Page size in KiB to configure jemalloc for.
+  # Defaults to 64 on architectures where 64KB pages are common, 4 otherwise.
+  # Note that a higher value is compatible with lower page sizes but may waste memory.
+  pageSizeKiB ?
+    if
+      (
+        stdenv.hostPlatform.isAarch64 || stdenv.hostPlatform.isLoongArch64 || stdenv.hostPlatform.isPower64
+      )
+    then
+      64
+    else
+      4,
 }:
 
+let
+  pageSizeMap = {
+    "4" = 12;
+    "16" = 14;
+    "64" = 16;
+  };
+in
+assert lib.asserts.assertOneOf "pageSizeKiB" (toString pageSizeKiB) (
+  builtins.attrNames pageSizeMap
+);
+
 stdenv.mkDerivation (finalAttrs: {
   pname = "jemalloc";
   version = "5.3.0-unstable-2025-09-12";
@@ -54,16 +77,7 @@ stdenv.mkDerivation (finalAttrs: {
   # https://github.com/jemalloc/jemalloc/issues/467
   # https://sources.debian.org/src/jemalloc/5.3.0-3/debian/rules/
   ++ [
-    (
-      if
-        (
-          stdenv.hostPlatform.isAarch64 || stdenv.hostPlatform.isLoongArch64 || stdenv.hostPlatform.isPower64
-        )
-      then
-        "--with-lg-page=16"
-      else
-        "--with-lg-page=12"
-    )
+    "--with-lg-page=${toString pageSizeMap."${toString pageSizeKiB}"}"
   ]
   # See https://github.com/jemalloc/jemalloc/issues/1997
   # Using a value of 48 should work on both emulated and native x86_64-darwin.