diff --git a/compiler/rustc/src/main.rs b/compiler/rustc/src/main.rs
index e21c9b66044..f5536b78beb 100644
--- a/compiler/rustc/src/main.rs
+++ b/compiler/rustc/src/main.rs
@@ -24,6 +24,15 @@
 // The two crates we link to here, `std` and `rustc_driver`, are both dynamic
 // libraries. So we must reference jemalloc symbols one way or another, because
 // this file is the only object code in the rustc executable.
+//
+// NOTE: if you are reading this comment because you want to set a custom `global_allocator` for
+// benchmarking, consider using the benchmarks in the `rustc-perf` collector suite instead:
+// https://github.com/rust-lang/rustc-perf/blob/master/collector/README.md#profiling
+//
+// NOTE: if you are reading this comment because you want to replace jemalloc with another allocator
+// to compare their performance, see
+// https://github.com/fee1-dead-contrib/rust/commit/b90cfc887c31c3e7a9e6d462e2464db1fe506175#diff-43914724af6e464c1da2171e4a9b6c7e607d5bc1203fa95c0ab85be4122605ef
+// for an example of how to do so.
 
 #[unix_sigpipe = "sig_dfl"]
 fn main() {