diff --git a/pageserver/src/tenant/ephemeral_file.rs b/pageserver/src/tenant/ephemeral_file.rs
index 6e36b97560..7f4bf6b9aa 100644
--- a/pageserver/src/tenant/ephemeral_file.rs
+++ b/pageserver/src/tenant/ephemeral_file.rs
@@ -384,7 +384,7 @@ mod tests {
 
         let cap = file.buffered_writer.inspect_mutable().capacity();
 
-        let write_nbytes = cap + cap / 2;
+        let write_nbytes = cap * 2 + cap / 2;
 
         let content: Vec<u8> = rand::thread_rng()
             .sample_iter(rand::distributions::Standard)
@@ -411,10 +411,13 @@ mod tests {
         }
 
         let file_contents = std::fs::read(file.buffered_writer.as_inner().path()).unwrap();
-        assert_eq!(file_contents, &content[0..cap]);
+        assert!(file_contents == &content[0..cap] || file_contents == &content[0..cap * 2]);
 
-        let buffer_contents = file.buffered_writer.inspect_mutable();
-        assert_eq!(buffer_contents, &content[cap..write_nbytes]);
+        let maybe_flushed_buffer_contents = file.buffered_writer.inspect_maybe_flushed().unwrap();
+        assert_eq!(maybe_flushed_buffer_contents, &content[cap..cap * 2]);
+
+        let mutable_buffer_contents = file.buffered_writer.inspect_mutable();
+        assert_eq!(mutable_buffer_contents, &content[cap * 2..write_nbytes]);
     }
 
     #[tokio::test]
@@ -428,11 +431,12 @@ mod tests {
                 .await
                 .unwrap();
 
+        // mutable buffer and maybe_flushed buffer each has cap.
         let cap = file.buffered_writer.inspect_mutable().capacity();
 
         let content: Vec<u8> = rand::thread_rng()
             .sample_iter(rand::distributions::Standard)
-            .take(cap + cap / 2)
+            .take(cap * 2 + cap / 2)
             .collect();
 
         file.write_raw(&content, &ctx).await.unwrap();
@@ -440,17 +444,20 @@ mod tests {
         // assert the state is as this test expects it to be
         assert_eq!(
             &file.load_to_io_buf(&ctx).await.unwrap(),
-            &content[0..cap + cap / 2]
+            &content[0..cap * 2 + cap / 2]
         );
         let md = file.buffered_writer.as_inner().path().metadata().unwrap();
+        assert!(
+            md.len() == cap.into_u64() || md.len() == 2 * cap.into_u64(),
+            "buffered writer requires one write to be flushed if we write 2.5x buffer capacity"
+        );
         assert_eq!(
-            md.len(),
-            cap.into_u64(),
-            "buffered writer does one write if we write 1.5x buffer capacity"
+            &file.buffered_writer.inspect_maybe_flushed().unwrap()[0..cap],
+            &content[cap..cap * 2]
         );
         assert_eq!(
             &file.buffered_writer.inspect_mutable()[0..cap / 2],
-            &content[cap..cap + cap / 2]
+            &content[cap * 2..cap * 2 + cap / 2]
         );
     }
 
@@ -475,7 +482,7 @@ mod tests {
 
         let content: Vec<u8> = rand::thread_rng()
             .sample_iter(rand::distributions::Standard)
-            .take(cap + cap / 2)
+            .take(cap * 2 + cap / 2)
             .collect();
 
         file.write_raw(&content, &ctx).await.unwrap();
@@ -505,9 +512,17 @@ mod tests {
         test_read(cap - 10, 10).await;
         // read across file and buffer
         test_read(cap - 10, 20).await;
-        // stay from start of buffer
+        // stay from start of maybe flushed buffer
         test_read(cap, 10).await;
-        // completely within buffer
+        // completely within maybe flushed buffer
         test_read(cap + 10, 10).await;
+        // border onto edge of maybe flushed buffer.
+        test_read(cap * 2 - 10, 10).await;
+        // read across maybe flushed and mutable buffer
+        test_read(cap * 2 - 10, 20).await;
+        // read across three segments
+        test_read(cap - 10, cap + 20).await;
+        // completely within mutable buffer
+        test_read(cap * 2 + 10, 10).await;
     }
 }
diff --git a/pageserver/src/virtual_file/owned_buffers_io/write.rs b/pageserver/src/virtual_file/owned_buffers_io/write.rs
index cf0157bd75..f0399681f1 100644
--- a/pageserver/src/virtual_file/owned_buffers_io/write.rs
+++ b/pageserver/src/virtual_file/owned_buffers_io/write.rs
@@ -121,7 +121,7 @@ where
         let chunk_len = chunk.len();
         // avoid memcpy for the middle of the chunk
         if chunk.len() >= self.mutable().cap() {
-            // TODO(yuchen): do we still want to keep this?
+            // TODO(yuchen): do we still want to keep the bypass path?
             self.flush(ctx).await?;
             // do a big write, bypassing `buf`
             assert_eq!(
diff --git a/pageserver/src/virtual_file/owned_buffers_io/write/flush.rs b/pageserver/src/virtual_file/owned_buffers_io/write/flush.rs
index 9b5f36a5d3..a9c1404712 100644
--- a/pageserver/src/virtual_file/owned_buffers_io/write/flush.rs
+++ b/pageserver/src/virtual_file/owned_buffers_io/write/flush.rs
@@ -42,6 +42,7 @@ impl<S: Send, R: Send> Duplex<S, R> {
     }
 }
 
+// TODO(yuchen): special actions in drop to clean up the join handle?
 pub struct FlushHandleInner<Buf, W> {
     /// A bi-directional channel that sends (buffer, offset) for writes,
     /// and receives recyled buffer.