v20260406-0003-Add-more-diagnostics-about-shared-memory-s.patch

From 1d1d85f1c36bb86b4648c5c5c3afb4b41b0f7c2a Mon Sep 17 00:00:00 2001
From: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Date: Mon, 6 Apr 2026 10:58:29 +0530
Subject: [PATCH v20260406 3/6] Add more diagnostics about shared memory
 segments

NOT FOR FINAL COMMIT

Log size, RSS and Swap of every shared memory segment mapped by the backend.
This will be useful to understand the failure on CFBot where we are seeing about
10MB extra shared memory allocated that expected.
---
 .../modules/resizable_shmem/resizable_shmem.c | 93 +++++++++++++++++--
 1 file changed, 84 insertions(+), 9 deletions(-)

diff --git a/src/test/modules/resizable_shmem/resizable_shmem.c b/src/test/modules/resizable_shmem/resizable_shmem.c
index 2063d05053f..66754582b32 100644
--- a/src/test/modules/resizable_shmem/resizable_shmem.c
+++ b/src/test/modules/resizable_shmem/resizable_shmem.c
@@ -254,8 +254,11 @@ resizable_shmem_read(PG_FUNCTION_ARGS)
  * backend.
  *
  * The VMA containing our resizable_shmem pointer is used to determine the main
- * memory segment.  RSS + Swap (in bytes) for that VMS from  /proc/self/smaps is
+ * memory segment.  RSS + Swap (in bytes) for that VMA from /proc/self/smaps is
  * returned.
+ *
+ * As a side effect, all shared-memory VMAs are logged with their name, RSS,
+ * and Swap values for diagnostic purposes.
  */
 Datum
 resizable_shmem_usage(PG_FUNCTION_ARGS)
@@ -268,6 +271,14 @@ resizable_shmem_usage(PG_FUNCTION_ARGS)
 	bool		in_target_vma = false;
 	size_t		result;
 
+	/* State for logging shared VMAs */
+	bool		in_shared_vma = false;
+	char		vma_name[256];
+	char		vma_range[64];
+	int64		vma_size_kb = -1;
+	int64		vma_rss_kb = -1;
+	int64		vma_swap_kb = -1;
+
 	f = fopen("/proc/self/smaps", "r");
 	if (f == NULL)
 		ereport(ERROR,
@@ -278,22 +289,86 @@ resizable_shmem_usage(PG_FUNCTION_ARGS)
 	{
 		unsigned long start;
 		unsigned long end;
+		char		perms[5];
+		unsigned long offset;
+		char		dev[12];
+		unsigned long inode;
+		char		pathname[256];
+		int			nfields;
 
-		if (sscanf(line, "%lx-%lx", &start, &end) == 2)
+		nfields = sscanf(line, "%lx-%lx %4s %lx %11s %lu %255[^\n]",
+						 &start, &end, perms, &offset, dev, &inode, pathname);
+
+		if (nfields >= 6)
 		{
+			/*
+			 * We've hit a new VMA header.  First, log the previous shared VMA
+			 * if we were tracking one.
+			 */
+			if (in_shared_vma)
+				elog(LOG, "shared VMA %s %s: Size=%ld kB, Rss=%ld kB, Swap=%ld kB",
+					 vma_range, vma_name,
+					 (long) (vma_size_kb >= 0 ? vma_size_kb : 0),
+					 (long) (vma_rss_kb >= 0 ? vma_rss_kb : 0),
+					 (long) (vma_swap_kb >= 0 ? vma_swap_kb : 0));
+
+			/* Check if this VMA is a shared mapping (has 's' in perms) */
+			in_shared_vma = (perms[3] == 's');
+			if (in_shared_vma)
+			{
+				snprintf(vma_range, sizeof(vma_range), "%lx-%lx", start, end);
+				if (nfields >= 7)
+					strlcpy(vma_name, pathname, sizeof(vma_name));
+				else
+					strlcpy(vma_name, "(anonymous)", sizeof(vma_name));
+				vma_size_kb = -1;
+				vma_rss_kb = -1;
+				vma_swap_kb = -1;
+			}
+
+			/* Track the target VMA for our return value */
 			in_target_vma = (target >= start && target < end);
+			if (in_target_vma)
+			{
+				rss_kb = -1;
+				swap_kb = -1;
+			}
 		}
-		else if (in_target_vma)
+		else
 		{
-			if (rss_kb == -1)
-				sscanf(line, "Rss: %ld kB", &rss_kb);
-			if (swap_kb == -1)
-				sscanf(line, "Swap: %ld kB", &swap_kb);
-			if (rss_kb >= 0 && swap_kb >= 0)
-				break;
+			/* Parse detail lines for the current VMA */
+			int64		val;
+
+			if (sscanf(line, "Size: %ld kB", &val) == 1)
+			{
+				if (in_shared_vma && vma_size_kb == -1)
+					vma_size_kb = val;
+			}
+			else if (sscanf(line, "Rss: %ld kB", &val) == 1)
+			{
+				if (in_target_vma && rss_kb == -1)
+					rss_kb = val;
+				if (in_shared_vma && vma_rss_kb == -1)
+					vma_rss_kb = val;
+			}
+			else if (sscanf(line, "Swap: %ld kB", &val) == 1)
+			{
+				if (in_target_vma && swap_kb == -1)
+					swap_kb = val;
+				if (in_shared_vma && vma_swap_kb == -1)
+					vma_swap_kb = val;
+			}
 		}
 	}
 
+	/* Log the last shared VMA if any */
+	if (in_shared_vma)
+		elog(LOG, "shared VMA %s %s: Size=%ld kB, Rss=%ld kB, Swap=%ld kB",
+			 vma_range, vma_name,
+			 (long) (vma_size_kb >= 0 ? vma_size_kb : 0),
+			 (long) (vma_rss_kb >= 0 ? vma_rss_kb : 0),
+			 (long) (vma_swap_kb >= 0 ? vma_swap_kb : 0));
+
 	fclose(f);
 
 	result = rss_kb >= 0 ? mul_size(rss_kb, 1024) : 0;
-- 
2.34.1