Memory Overcommitment Indicators — Interpreting MEMCTL and SWPOUT
Exhibit
Refer to the exhibit. ``` esxtop -b -d 30 -n 2 > /tmp/perf.csv # Sample output (abbreviated): # CPU(%): 10.5, 12.3, 8.9, ... # PMEM(%): 65, 70, 68, ... # MEMCTL(%): 5, 4, 3, ... # SWPOUT(%): 2, 1, 0, ... ```
Refer to the exhibit. The performance data shows MEMCTL at 5% and SWPOUT at 2%. What does this indicate about the host?
Quick Answer
The host is over-committed on memory, causing ballooning and swapping. MEMCTL at 5% means the vmmemctl balloon driver is actively reclaiming memory from VMs, while SWPOUT at 2% indicates the hypervisor is swapping guest memory to disk—together, these metrics confirm the host has exhausted its physical memory and is using both techniques to compensate. On the VCP-DCV exam, this scenario tests your ability to distinguish between ballooning (a cooperative, driver-based reclaim) and swapping (a last-resort, performance-impacting mechanism); a common trap is assuming low percentages are harmless, but any non-zero SWPOUT signals memory pressure. For the exam, remember the mnemonic: “Balloon before swap, swap means stop”—ballooning is the first line of defense, but swapping always indicates critical overcommitment.
⚠ Common exam trap
It's easy for candidates to confuse memory over-commitment indicators (MEMCTL, SWPOUT) with CPU or storage performance metrics, leading them to select CPU contention or storage latency options instead of recognizing the specific memory reclamation counters.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The host is over-committed on memory, causing ballooning and swapping.
MEMCTL at 5% indicates the ESXi host's memory balloon driver (vmmemctl) is actively reclaiming memory from virtual machines, while SWPOUT at 2% shows the host is swapping guest memory to disk. Together, these values confirm the host is over-committed on memory, forcing the hypervisor to use both ballooning and swapping to free up memory for VMs.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The host is over-committed on memory, causing ballooning and swapping.
Why this is correct
MEMCTL at 5% reflects the balloon driver reclaiming guest memory, while SWPOUT at 2% confirms the hypervisor is swapping to disk. Together these counters indicate the host has over-committed physical memory beyond what its workload demands, so ESXi is actively reclaiming pages to satisfy the configured memory constraint.
- ✗
The host is experiencing CPU contention.
Why it's wrong here
MEMCTL at 5% and SWPOUT at 2% are both low memory-contention readings, so they do not evidence CPU contention. CPU contention would be shown by CPU ready time or co-stop values. The option is tempting because memory pressure can indirectly drive CPU overhead, but these counters specifically track memory control and swap activity.
- ✗
The host has network congestion.
Why it's wrong here
MEMCTL and SWPOUT are memory-subsystem counters, not network counters, so they cannot indicate network congestion. Network congestion would appear as dropped packets or high NIC utilisation. The option is tempting because swap traffic traverses the network stack, but these specific metrics measure guest memory pressure, not link saturation.
- ✗
The host has high storage latency.
Why it's wrong here
MEMCTL at 5% and SWPOUT at 2% are memory-contention and swap-out metrics, both low, so they say nothing about storage latency. Storage latency would be indicated by DAVG or KAVG counters instead. The option is tempting because swap-out does touch disk, but at 2% it is negligible.
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Same concept, more angles
2 more ways this is tested on VCP-DCV
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which THREE memory-related metrics in esxtop indicate that a virtual machine is experiencing memory pressure? (Choose three.)
medium- ✓ A.SWCUR
- B.%SYS
- ✓ C.ACTV
- ✓ D.MCTLSZ
- E.%RDY
Why A: SWCUR (current swapped memory) indicates that the VM has swapped memory to disk, a clear sign of memory pressure. MCTLSZ (memory balloon driver size) shows the amount of memory reclaimed by the balloon driver due to contention, also indicating pressure. ACTV (active memory) when high relative to the VM's configured memory can indicate that the VM is actively using memory and may be under pressure, especially when combined with other metrics. %SYS and %RDY are CPU-related metrics and not relevant to memory pressure.
Variation 2. A VM with a large memory footprint is experiencing high swap rates. The host has free memory but the swap rate is still high. What is the most likely cause?
medium- A.The VM's virtual machine swap file is on a slow datastore.
- ✓ B.The VM's memory limit is set too low.
- C.The host is using software iSCSI causing high latency.
- D.The VM's memory reservation is set too high.
Why B: A VM memory limit in vSphere caps the amount of host physical memory the VM can consume. When the limit is lower than the guest's working set, the VM balloons and then swaps to its .vswp file even though the host has free memory, because the limit — not host pressure — is driving reclamation. Raising or removing the limit resolves the swap.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This VCP-DCV practice question is part of Courseiva's free VMware certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the VCP-DCV exam.