Seems to work

pgxn/neon/communicator/src/neon_request.rs

@@ -185,6 +185,7 @@ pub struct CReadSlruSegmentRequest {
     pub request_id: u64,
     pub slru_kind: SlruKind,
     pub segment_number: u32,
+    pub request_lsn: CLsn,
 
     // pub spc_oid: COid,
     // pub db_oid: COid,

pgxn/neon/communicator/src/worker_process/main_loop.rs

@@ -427,7 +427,7 @@ impl<'t> CommunicatorWorkerProcessStruct<'t> {
             }
             NeonIORequest::ReadSlruSegment(req) => {
                 self.request_read_slru_segment_counter.inc();
-                let lsn = self.cache.get_lsn();
+                let lsn = Lsn(req.request_lsn);
 
                 match self
                     .client
@@ -447,7 +447,7 @@ impl<'t> CommunicatorWorkerProcessStruct<'t> {
                             std::ptr::copy_nonoverlapping(src.as_ptr(), dest.as_mut_ptr(), len);
                         };
 
-                        let blocks_count = len / (crate::BLCKSZ * crate::SLRU_PAGES_PER_SEGMENT);
+                        let blocks_count = len / crate::BLCKSZ;
 
                         NeonIOResult::ReadSlruSegment(blocks_count as _)
                     }

pgxn/neon/communicator_new.c

@@ -997,7 +997,6 @@ communicator_new_dbsize(Oid dbNode)
 }
 
 int
-// communicator_new_read_slru_segment(SlruKind kind, uint32_t segno, void *buffer)
 communicator_new_read_slru_segment(
 	SlruKind kind,
 	uint32_t segno,
@@ -1011,7 +1010,8 @@ communicator_new_read_slru_segment(
 			.request_id = assign_request_id(),
 			.slru_kind = kind,
 			.segment_number = segno,
-			.dest.ptr = buffer,
+			.request_lsn = request_lsns->request_lsn,
+			.dest.ptr = bounce_buf(),
 		}
 	};
 
@@ -1021,9 +1021,11 @@ communicator_new_read_slru_segment(
 	XLogSetAsyncXactLSN(request_lsns->request_lsn);
 
 	perform_request(&request, &result);
+
 	switch (result.tag)
 	{
 		case NeonIOResult_ReadSlruSegment:
+			memcpy(buffer, request.read_slru_segment.dest.ptr, 8192);
 			return result.read_slru_segment;
 		case NeonIOResult_Error:
 			ereport(ERROR,
@@ -1035,6 +1037,8 @@ communicator_new_read_slru_segment(
 			elog(ERROR, "unexpected result for read SLRU operation: %d", result.tag);
 			break;
 	}
+
+	return 0;
 }
 
 /* Write requests */

pgxn/neon/communicator_new.h

@@ -38,8 +38,6 @@ extern void communicator_new_prefetch_register_bufferv(NRelFileInfo rinfo, ForkN
 													   BlockNumber nblocks);
 extern bool communicator_new_cache_contains(NRelFileInfo rinfo, ForkNumber forkNum,
 											BlockNumber blockno);
-// extern int	communicator_new_read_slru_segment(SlruKind kind, uint32_t segno,
-// 											   void *buffer);
 extern int communicator_new_read_slru_segment(
 	SlruKind kind,
 	uint32_t segno,