From 902bdd92c21edfb4628599ce2535e39567769e02 Mon Sep 17 00:00:00 2001
From: rcourtman <courtmanr@gmail.com>
Date: Wed, 4 Feb 2026 12:08:33 +0000
Subject: [PATCH] fix: prefer status-mem over status-freemem for VM memory
 calculation

Proxmox's FreeMem field reports free memory relative to the balloon's
guest-visible total (total_mem), not relative to MaxMem. When ballooning
is active and the VM's memory has been reduced, subtracting FreeMem from
MaxMem produces wildly inflated usage (e.g. 97% when actual usage is 20%).

Proxmox's Mem field is already calculated as (total_mem - free_mem),
giving the correct used bytes regardless of balloon state. Swap the
priority so Mem is checked before FreeMem.

Related to #1185
---
 internal/monitoring/monitor.go         | 13 ++++++++++---
 internal/monitoring/monitor_polling.go | 13 ++++++++++---
 2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/internal/monitoring/monitor.go b/internal/monitoring/monitor.go
index a0f65a848e..715bdf505a 100644
--- a/internal/monitoring/monitor.go
+++ b/internal/monitoring/monitor.go
@@ -6647,12 +6647,19 @@ func (m *Monitor) pollVMsAndContainersEfficient(ctx context.Context, instanceNam
 							memAvailable = memTotal
 						}
 						memUsed = memTotal - memAvailable
+					case detailedStatus.Mem > 0:
+						// Prefer Mem over FreeMem: Proxmox calculates Mem as
+						// (total_mem - free_mem) using the balloon's guest-visible
+						// total, which is correct even when ballooning is active.
+						// FreeMem is relative to the balloon allocation (not MaxMem),
+						// so subtracting it from MaxMem produces wildly inflated
+						// usage when the balloon has reduced the VM's memory.
+						// Refs: #1185
+						memUsed = detailedStatus.Mem
+						memorySource = "status-mem"
 					case detailedStatus.FreeMem > 0 && memTotal >= detailedStatus.FreeMem:
 						memUsed = memTotal - detailedStatus.FreeMem
 						memorySource = "status-freemem"
-					case detailedStatus.Mem > 0:
-						memUsed = detailedStatus.Mem
-						memorySource = "status-mem"
 					}
 					if memUsed > memTotal {
 						memUsed = memTotal
diff --git a/internal/monitoring/monitor_polling.go b/internal/monitoring/monitor_polling.go
index ff672873cf..c417c6cb1f 100644
--- a/internal/monitoring/monitor_polling.go
+++ b/internal/monitoring/monitor_polling.go
@@ -364,12 +364,19 @@ func (m *Monitor) pollVMsWithNodes(ctx context.Context, instanceName string, clu
 								memAvailable = memTotal
 							}
 							memUsed = memTotal - memAvailable
+						case vmStatus.Mem > 0:
+							// Prefer Mem over FreeMem: Proxmox calculates Mem as
+							// (total_mem - free_mem) using the balloon's guest-visible
+							// total, which is correct even when ballooning is active.
+							// FreeMem is relative to the balloon allocation (not MaxMem),
+							// so subtracting it from MaxMem produces wildly inflated
+							// usage when the balloon has reduced the VM's memory.
+							// Refs: #1185
+							memUsed = vmStatus.Mem
+							memorySource = "status-mem"
 						case vmStatus.FreeMem > 0:
 							memUsed = memTotal - vmStatus.FreeMem
 							memorySource = "status-freemem"
-						case vmStatus.Mem > 0:
-							memUsed = vmStatus.Mem
-							memorySource = "status-mem"
 						default:
 							memUsed = 0
 							memorySource = "status-unavailable"