From ff27e95cb0629e58cdb14415510ce33005061780 Mon Sep 17 00:00:00 2001
From: Kevin Longe <273747162+kvlonge@users.noreply.github.com>
Date: Mon, 9 Nov 2026 12:48:05 +0000
Subject: [PATCH] perf: stop mimalloc asking for transparent huge pages

mimalloc madvises its 1 GiB arenas for transparent huge pages, so on
Linux hosts with THP in madvise mode (the Ubuntu default) every partly
used 2 MiB page stayed resident in full. A cold 10,000-model compile
held about 470 MiB of huge pages at its peak. Building mimalloc with
no_thp keeps those arenas on normal pages and lowers that compile's
peak memory by about 85 MB, with unchanged wall and CPU time. Other
platforms are unaffected.
---
 Cargo.toml | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Cargo.toml b/Cargo.toml
index 3f05fa9a2..a2451c352 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -81,7 +81,9 @@ globset = "0.4"
 junction = { version = "2.1.0", default-features = false }
 keyring = { version = "3.6.3", default-features = false }
 # Python loads the extension with dlopen, so mimalloc must not use initial-exec TLS.
-mimalloc = { version = "0.1", default-features = false, features = ["local_dynamic_tls"] }
+# no_thp: mimalloc otherwise asks for transparent huge pages on its 1 GiB arenas, and each
+# partly used 2 MiB page then stays resident in full, which raises peak memory.
+mimalloc = { version = "0.1", default-features = false, features = ["local_dynamic_tls", "no_thp"] }
 proc-macro2 = { version = "1", features = ["span-locations"] }
 pyo3 = { version = "0.26", features = ["abi3-py312"] }
 rpassword = "7.5.4"