All Products
Search

This Product

    Container Service for Kubernetes:Memory diagnostics

    Document Center

    Container Service for Kubernetes:Memory diagnostics

    Last Updated:Aug 25, 2026

    Identify memory leaks, fragmentation, and OOM errors in ACK clusters with visual diagnostics.

    Memory diagnostics covers three areas: memory overview, memory analysis, and OOM analysis. Inspect memory at both the node and pod level.

    Note

    Diagnostic items shown reflect your actual cluster configuration.

    Important

    When you run diagnostics, ACK collects data from each node, including system version, load status, Docker and kubelet status, and key error messages in system logs. ACK does not collect business data or sensitive information.

    Diagnostic workflow

    Use the three diagnostic areas in sequence to narrow down a memory issue:

    1. Memory overview — Check for memory risks: leaked memory, fragmentation, unreleased Memcg entries, and THP waste. Use charts to confirm whether abnormal usage is in kernel or application memory.

    2. Memory analysis — Drill down to process- and pod-level memory usage to identify which process or container consumes excessive anonymous memory, page cache, or shared memory.

    3. OOM analysis — Review OOM event counts and types to determine whether OOM errors occur at the node (Host) or container (cgroup) level, and which containers hit their memory limits.

    Memory overview

    Identifies memory risks across the following diagnostic items.

    Diagnostic item Description
    Leaked Memory Checks for kernel memory leaks in the Slab, Vmalloc, and buddy system (allocpage).
    Memory Usage Displays system memory utilization.
    Memcg Checks whether unreleased memory cgroups (Memcg) degrade system performance or cause statistical errors.
    Memory Fragmentation Checks for memory fragmentation that degrades system performance.
    THPZeroPage Evaluates the ratio of Transparent Huge Page (THP) waste.

    System memory usage is charted in three categories:

    • Kernel memory (kernel): total memory used by the OS kernel.

    • Application memory (app): total memory used by user-mode programs.

    • Free memory (free): total free system memory.

    Key concepts

    The following terms are used throughout memory diagnostics.

    Term Description
    Memory leak Occurs when dynamically allocated memory is never released, causing memory usage to grow continuously. Unresolved leaks degrade performance and can cause crashes.
    Memory utilization Memory utilization = (Total memory - Free memory) x 100 / Total memory. Page cache counts as free memory and does not affect utilization — the kernel can reclaim it at any time.
    Unreleased Memcg A memory cgroup not released due to a system exception. Can degrade system performance.
    Memory fragmentation Over time, free contiguous memory blocks become too small for large allocation requests. Delays allocation and causes application jitter.
    Ratio of THP waste Ratio of THP waste = Number of zero THPs x 100% / Total number of THPs. See THP details below.
    Buddy system Linux kernel algorithm for managing memory pages. Divides pages into 11 groups with power-of-two block sizes: 4 KB, 8 KB, 16 KB, 32 KB ... 4 MB. Most pages are 4 KB.
    Slab Allocates small memory pieces on top of the buddy system.
    Vmalloc Allocates memory with nonlinear mapping on top of the buddy system.
    Page cache (filecache) Linux caches file content in memory for faster subsequent access.
    Anonymous memory Memory dynamically allocated to a process's heap and stack through new, malloc, or mmap. Not backed by a file system.
    Shared memory A memory block shared by two or more processes for inter-process communication.
    tmpfs Linux temporary file system backed by memory. All reads and writes are cached in memory.
    hugetlb Memory consumed by huge pages in a file system.

    THP details

    Transparent Huge Pages (THP) are huge pages sized 2 MiB or 1 GiB in the kernel. Each subpage is 4 KiB, so one 2-MiB THP equals 512 subpages.

    With THP enabled, the kernel dynamically allocates THPs to reduce Translation Lookaside Buffer (TLB) misses and improve performance. However, THP can cause memory bloat and overcommitment: when an application requests only 8 KiB (2 subpages), the kernel allocates a full 2-MiB THP — leaving 510 zero subpages that waste resident set size (RSS) and can trigger OOM errors.

    Kernel memory metrics

    In most cases, memory leaks are indicated by abnormal usage in Sunreclaim or the buddy system. Monitor these metrics closely.

    Metric Description
    SReclaimable Memory that the Slab can reclaim.
    Sunreclaim Memory that the Slab cannot reclaim. Abnormal growth strongly indicates a kernel memory leak.
    PageTables Memory occupied by kernel page tables.
    Vmalloc Memory allocated by Vmalloc.
    KernelStack Total kernel stack memory used by processes.
    AllocPages Memory allocated from the buddy system by functions such as alloc_pages. Not retrievable through any node file — excessive use creates a memory black hole.

    Application memory metrics

    When analyzing user-mode memory usage, focus on anonymous memory, shared memory, and page cache.

    Metric Description
    filecache Page cache that can be reclaimed by running drop caches.
    anon Anonymous memory used by a program's heap and stack. High usage suggests a process memory leak or enabled THP.
    mlock Memory locked by the system.
    huge Memory used by huge pages.
    buffer Memory used by block device and file system metadata.
    shmem Shared memory (tmpfs). Leaks occur if a tmpfs file is not deleted after the process exits, or if a file is deleted while still open.

    Memory analysis

    Provides two views: process memory and pod memory.

    Process memory

    Lists processes sorted by memory usage and breaks down anonymous memory, page cache, and shared memory.

    Pod memory

    Shows which files occupy page cache and shared memory in each container and pod, with active and inactive cache ratios.

    Diagnostic item Description
    Pod The name of the pod.
    Container The name of the container.
    File The full path of the file, including the file name.
    Cache The page cache (filecache) occupied by the file.
    Container Cache The container-level cache occupied by the file. Multiple processes in the same container may reference the same file.
    Active Cache Page cache currently in use.
    Inactive Cache Page cache not in use, eligible for reclaim.

    OOM analysis

    Diagnoses out-of-memory errors across the following items.

    Diagnostic item Description
    OS OOM Count Total OOM errors from host startup to diagnosis.
    Available Memory Current free system memory.
    Low Watermark The low memory threshold. When available memory drops below this value, the kernel triggers asynchronous memory reclaim.
    Container Pod name, container ID, or cgroup name.
    limit The memory limit configured for the container.
    usage Current memory used by the container.
    OOM Count Total OOM errors in the container.
    OOM Type The type of OOM error: Host or cgroup.