[Experiment] advise mmap to cleanup closed segments

Author: JojiiOfficial

src/lib.rs

@@ -572,6 +572,7 @@ fn close_segment(mut segment: OpenSegment, start_index: u64) -> Result<ClosedSeg
         .path()
         .with_file_name(format!("closed-{start_index}"));
     segment.segment.rename(new_path)?;
+    segment.segment.close();
     Ok(ClosedSegment {
         start_index,
         segment: segment.segment,

src/mmap_view_sync.rs

@@ -19,6 +19,14 @@ pub struct MmapViewSync {
 }
 
 impl MmapViewSync {
+    pub fn close(&self) {
+        unsafe {
+            let i = &mut *self.inner.get();
+            i.unchecked_advise(memmap2::UncheckedAdvice::DontNeed)
+                .unwrap();
+        }
+    }
+
     pub fn from_file(file: &File, offset: usize, capacity: usize) -> Result<MmapViewSync> {
         let mmap = unsafe {
             MmapOptions::new()

src/segment.rs

@@ -111,6 +111,10 @@ pub struct Segment {
 }
 
 impl Segment {
+    pub fn close(&self) {
+        self.mmap.close()
+    }
+
     /// Creates a new segment.
     ///
     /// The initial capacity must be at least 8 bytes.