diff --git a/pgxn/neon/communicator_new.c b/pgxn/neon/communicator_new.c
index bc27942bb1..d361ff7274 100644
--- a/pgxn/neon/communicator_new.c
+++ b/pgxn/neon/communicator_new.c
@@ -22,6 +22,7 @@
 #endif
 #include "access/xlog_internal.h"
 #include "access/xlogutils.h"
+#include "common/hashfn.h"
 #include "executor/instrument.h"
 #include "miscadmin.h"
 #include "postmaster/bgworker.h"
@@ -40,6 +41,7 @@
 #include "tcop/tcopprot.h"
 
 #include "communicator_new.h"
+#include "hll.h"
 #include "neon.h"
 #include "neon_perf_counters.h"
 #include "pagestore_client.h"
@@ -98,7 +100,19 @@ typedef struct CommunicatorShmemPerBackendData
 
 typedef struct CommunicatorShmemData
 {
-	int			dummy;
+	/*
+	 * Estimation of working set size.
+	 *
+	 * Note that this is not protected by any locks. That's sloppy, but works
+	 * fine in practice. To "add" a value to the HLL state, we just overwrite
+	 * one of the timestamps. Calculating the estimate reads all the values, but
+	 * it also doesn't depend on seeing a consistent snapshot of the values. We
+	 * could get bogus results if accessing the TimestampTz was not atomic, but
+	 * it on any 64-bit platforms we care about it is, and even if we observed a
+	 * torn read every now and then, it wouldn't affect the overall estimate
+	 * much.
+	 */
+	HyperLogLogState wss_estimation;
 
 	CommunicatorShmemPerBackendData backends[]; /* MaxProcs */
 
@@ -250,6 +264,9 @@ communicator_new_shmem_startup(void)
 	shmem_ptr = (char *) shmem_ptr + communicator_size;
 	shmem_size -= communicator_size;
 
+	/* Initialize hyper-log-log structure for estimating working set size */
+	initSHLL(&communicator_shmem_ptr->wss_estimation);
+
 	for (int i = 0; i < MaxProcs; i++)
 	{
 		InitSharedLatch(&communicator_shmem_ptr->backends[i].io_completion_latch);
@@ -743,6 +760,19 @@ communicator_new_read_at_lsnv(NRelFileInfo rinfo, ForkNumber forkNum, BlockNumbe
 		}
 	};
 
+	{
+		BufferTag tag;
+
+		CopyNRelFileInfoToBufTag(tag, rinfo);
+		tag.forkNum = forkNum;
+		for (int i = 0; i < nblocks; i++)
+		{
+			tag.blockNum = blockno;
+			addSHLL(&communicator_shmem_ptr->wss_estimation,
+					hash_bytes((uint8_t *) &tag, sizeof(tag)));
+		}
+	}
+
 	elog(DEBUG5, "getpagev called for rel %u/%u/%u.%u block %u (%u blocks)",
 		 RelFileInfoFmt(rinfo), forkNum, blockno, nblocks);
 
@@ -1357,3 +1387,14 @@ bounce_write_if_needed(void *buffer)
 	memcpy(p, buffer, BLCKSZ);
 	return p;
 }
+
+int32
+communicator_new_approximate_working_set_size_seconds(time_t duration, bool reset)
+{
+	int32		dc;
+
+	dc = (int32) estimateSHLL(&communicator_shmem_ptr->wss_estimation, duration);
+	if (reset)
+		memset(communicator_shmem_ptr->wss_estimation.regs, 0, sizeof(communicator_shmem_ptr->wss_estimation.regs));
+	return dc;
+}
diff --git a/pgxn/neon/communicator_new.h b/pgxn/neon/communicator_new.h
index 5b636b687a..dc38b3059e 100644
--- a/pgxn/neon/communicator_new.h
+++ b/pgxn/neon/communicator_new.h
@@ -54,4 +54,7 @@ extern void communicator_new_rel_truncate(NRelFileInfo rinfo, ForkNumber forkNum
 extern void communicator_new_rel_unlink(NRelFileInfo rinfo, ForkNumber forkNum, XLogRecPtr lsn);
 extern void communicator_new_forget_cache(NRelFileInfo rinfo, ForkNumber forkNum, BlockNumber nblocks, XLogRecPtr lsn);
 
+/* other functions */
+extern int32 communicator_new_approximate_working_set_size_seconds(time_t duration, bool reset);
+
 #endif							/* COMMUNICATOR_NEW_H */
diff --git a/pgxn/neon/file_cache.c b/pgxn/neon/file_cache.c
index e5e2bb9183..847e2ba9f6 100644
--- a/pgxn/neon/file_cache.c
+++ b/pgxn/neon/file_cache.c
@@ -2159,46 +2159,21 @@ local_cache_pages(PG_FUNCTION_ARGS)
 		SRF_RETURN_DONE(funcctx);
 }
 
-PG_FUNCTION_INFO_V1(approximate_working_set_size_seconds);
 
-Datum
-approximate_working_set_size_seconds(PG_FUNCTION_ARGS)
+int32
+lfc_approximate_working_set_size_seconds(time_t duration, bool reset)
 {
-	if (neon_enable_new_communicator)
-		elog(ERROR, "TODO: not implemented");
+	int32		dc;
 
-	if (lfc_size_limit != 0)
-	{
-		int32 dc;
-		time_t duration = PG_ARGISNULL(0) ? (time_t)-1 : PG_GETARG_INT32(0);
-		LWLockAcquire(lfc_lock, LW_SHARED);
-		dc = (int32) estimateSHLL(&lfc_ctl->wss_estimation, duration);
-		LWLockRelease(lfc_lock);
-		PG_RETURN_INT32(dc);
-	}
-	PG_RETURN_NULL();
-}
+	if (lfc_size_limit == 0)
+		return -1;
 
-PG_FUNCTION_INFO_V1(approximate_working_set_size);
-
-Datum
-approximate_working_set_size(PG_FUNCTION_ARGS)
-{
-	if (neon_enable_new_communicator)
-		elog(ERROR, "TODO: not implemented");
-
-	if (lfc_size_limit != 0)
-	{
-		int32 dc;
-		bool reset = PG_GETARG_BOOL(0);
-		LWLockAcquire(lfc_lock, reset ? LW_EXCLUSIVE : LW_SHARED);
-		dc = (int32) estimateSHLL(&lfc_ctl->wss_estimation, (time_t)-1);
-		if (reset)
-			memset(lfc_ctl->wss_estimation.regs, 0, sizeof lfc_ctl->wss_estimation.regs);
-		LWLockRelease(lfc_lock);
-		PG_RETURN_INT32(dc);
-	}
-	PG_RETURN_NULL();
+	LWLockAcquire(lfc_lock, LW_SHARED);
+	dc = (int32) estimateSHLL(&lfc_ctl->wss_estimation, duration);
+	if (reset)
+		memset(lfc_ctl->wss_estimation.regs, 0, sizeof lfc_ctl->wss_estimation.regs);
+	LWLockRelease(lfc_lock);
+	return dc;
 }
 
 PG_FUNCTION_INFO_V1(get_local_cache_state);
diff --git a/pgxn/neon/file_cache.h b/pgxn/neon/file_cache.h
index 1b6ff36164..a5ffa6ea92 100644
--- a/pgxn/neon/file_cache.h
+++ b/pgxn/neon/file_cache.h
@@ -52,6 +52,9 @@ extern void lfc_prewarm(FileCacheState* fcs, uint32 n_workers);
 
 PGDLLEXPORT void lfc_prewarm_main(Datum main_arg);
 
+extern int32 lfc_approximate_working_set_size_seconds(time_t duration, bool reset);
+
+
 static inline bool
 lfc_read(NRelFileInfo rinfo, ForkNumber forkNum, BlockNumber blkno,
 		 void *buffer)
diff --git a/pgxn/neon/neon.c b/pgxn/neon/neon.c
index ab51abc1de..548bdd9bb8 100644
--- a/pgxn/neon/neon.c
+++ b/pgxn/neon/neon.c
@@ -583,6 +583,8 @@ _PG_init(void)
 PG_FUNCTION_INFO_V1(pg_cluster_size);
 PG_FUNCTION_INFO_V1(backpressure_lsns);
 PG_FUNCTION_INFO_V1(backpressure_throttling_time);
+PG_FUNCTION_INFO_V1(approximate_working_set_size_seconds);
+PG_FUNCTION_INFO_V1(approximate_working_set_size);
 
 Datum
 pg_cluster_size(PG_FUNCTION_ARGS)
@@ -629,6 +631,40 @@ backpressure_throttling_time(PG_FUNCTION_ARGS)
 	PG_RETURN_UINT64(BackpressureThrottlingTime());
 }
 
+Datum
+approximate_working_set_size_seconds(PG_FUNCTION_ARGS)
+{
+	time_t		duration;
+	int32		dc;
+
+	duration = PG_ARGISNULL(0) ? (time_t) -1 : PG_GETARG_INT32(0);
+
+	if (neon_enable_new_communicator)
+		dc = communicator_new_approximate_working_set_size_seconds(duration, false);
+	else
+		dc = lfc_approximate_working_set_size_seconds(duration, false);
+	if (dc < 0)
+		PG_RETURN_NULL();
+	else
+		PG_RETURN_INT32(dc);
+}
+
+Datum
+approximate_working_set_size(PG_FUNCTION_ARGS)
+{
+	int32		dc;
+	bool		reset = PG_GETARG_BOOL(0);
+
+	if (neon_enable_new_communicator)
+		dc = communicator_new_approximate_working_set_size_seconds(-1, reset);
+	else
+		dc = lfc_approximate_working_set_size_seconds(-1, reset);
+	if (dc < 0)
+		PG_RETURN_NULL();
+	else
+		PG_RETURN_INT32(dc);
+}
+
 static void
 neon_shmem_request(void)
 {