feat(hotpath): use mimalloc in inner counting allocator (#5523)

* feat(hotpath): use mimalloc in counting allocator

* fix(hotpath): adapt mimalloc for allocation counting

---------

Co-authored-by: overtrue <anzhengchao@gmail.com>

rustfs/src/main.rs

@@ -12,9 +12,32 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+#[cfg(all(feature = "hotpath", feature = "hotpath-alloc"))]
+use std::alloc::{GlobalAlloc, Layout};
+
+#[cfg(all(feature = "hotpath", feature = "hotpath-alloc"))]
+#[derive(Default)]
+struct DefaultMiMalloc;
+
+#[cfg(all(feature = "hotpath", feature = "hotpath-alloc"))]
+// SAFETY: allocation and deallocation are forwarded unchanged to MiMalloc, so
+// MiMalloc's GlobalAlloc guarantees apply to every returned pointer and layout.
+#[allow(unsafe_code)]
+unsafe impl GlobalAlloc for DefaultMiMalloc {
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        // SAFETY: the caller upholds GlobalAlloc's contract for layout.
+        unsafe { mimalloc::MiMalloc.alloc(layout) }
+    }
+
+    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
+        // SAFETY: ptr and layout came from this allocator and are forwarded unchanged.
+        unsafe { mimalloc::MiMalloc.dealloc(ptr, layout) }
+    }
+}
+
 #[cfg(all(feature = "hotpath", feature = "hotpath-alloc"))]
 #[global_allocator]
-static GLOBAL: hotpath::CountingAllocator = hotpath::CountingAllocator::new();
+static GLOBAL: hotpath::CountingAllocator<DefaultMiMalloc> = hotpath::CountingAllocator::new();
 
 #[cfg(not(all(feature = "hotpath", feature = "hotpath-alloc")))]
 #[global_allocator]
@@ -25,3 +48,15 @@ fn main() {
 
     rustfs::startup_entrypoint::run_process();
 }
+
+#[cfg(all(test, feature = "hotpath", feature = "hotpath-alloc"))]
+mod tests {
+    #[test]
+    #[allow(unsafe_code)]
+    fn hotpath_allocator_uses_mimalloc() {
+        let allocation = Box::new([0_u8; 64]);
+
+        // SAFETY: the live Box pointer is valid to inspect for heap ownership.
+        assert!(unsafe { libmimalloc_sys::mi_is_in_heap_region(allocation.as_ptr().cast()) });
+    }
+}