lsmem

Overview

The lsmem command displays information about memory ranges and their online/offline status. It’s particularly useful for systems with memory hotplug capabilities and NUMA architectures.

Syntax

lsmem [options]

Common Options

Option Description
-a List all memory ranges
-b Show output in bytes
-h Human-readable sizes
-o columns Specify output columns
-r Raw output format
-S Split by node
-s Show summary only
--sysroot=dir Use alternative sysfs root

Output Columns

Column Description
RANGE Memory address range
SIZE Size of memory range
STATE Online/Offline status
REMOVABLE Whether memory can be removed
BLOCK Memory block number
NODE NUMA node number
ZONES Memory zones

Key Use Cases

  1. Memory inventory
  2. NUMA topology analysis
  3. Memory hotplug management
  4. System capacity planning
  5. Memory troubleshooting

Examples with Explanations

Example 1: Basic Memory Information

lsmem

Shows memory ranges and their status

Example 2: Human-Readable Sizes

lsmem -h

Displays memory sizes in human-readable format (KB, MB, GB)

Example 3: Summary Only

lsmem -s

Shows only summary information

Understanding Memory States

State Description
online Memory is available for use
offline Memory is not available
going-offline Memory is being taken offline
going-online Memory is being brought online

Memory Block Management

Memory is managed in blocks: - Block size typically 128MB or 256MB - Blocks can be individually onlined/offlined - Useful for memory hotplug operations

Common Usage Patterns

  1. Check total memory:

    lsmem -s | grep "Total online memory"

  2. List offline memory:

    lsmem | grep offline

  3. Show NUMA distribution:

    lsmem -S

NUMA Memory Information

For NUMA systems: - Shows memory distribution across nodes - Helps with memory locality optimization - Useful for performance tuning

Memory Hotplug Operations

  1. Check removable memory:

    lsmem | grep "yes" | grep "REMOVABLE"

  2. Find offline blocks:

    lsmem -a | awk '$3=="offline" {print $4}'

Performance Analysis

Memory information useful for: - Memory bandwidth optimization - NUMA-aware application tuning - Memory pressure analysis - Capacity planning

Additional Resources

Best Practices

  1. Monitor memory hotplug status
  2. Understand NUMA topology
  3. Check removable memory before maintenance
  4. Use with other memory analysis tools
  5. Consider memory block alignment

Scripting Examples

  1. Count online memory blocks:

    lsmem | grep -c "online"

  2. Get total memory size:

    lsmem -s | grep "Total online memory" | awk '{print $4}'

  3. Check NUMA nodes:

    lsmem -o NODE | grep -v NODE | sort -u

Memory Zones

Common memory zones: - DMA: Direct Memory Access zone - DMA32: 32-bit DMA zone - Normal: Regular memory zone - HighMem: High memory zone (32-bit systems) - Movable: Memory that can be migrated

System Integration

  1. Memory monitoring:

    watch -n 5 'lsmem -s'

  2. NUMA optimization:

    lsmem -S | grep "node 0"

  3. Capacity reporting:

    echo "Total Memory: $(lsmem -s | grep 'Total online' | awk '{print $4}')"

Troubleshooting

  1. Memory not showing up
  2. Offline memory blocks
  3. NUMA node misalignment
  4. Memory hotplug failures
  5. Inconsistent memory reporting

Advanced Usage

  1. Custom column output:

    lsmem -o RANGE,SIZE,STATE,NODE

  2. Raw format for parsing:

    lsmem -r

  3. Alternative sysfs root:

    lsmem --sysroot=/alternative/path

Memory Block Operations

To manage memory blocks (requires root):

# Online a memory block
echo online > /sys/devices/system/memory/memory64/state

# Offline a memory block
echo offline > /sys/devices/system/memory/memory64/state

Integration Examples

  1. With NUMA tools:

    lsmem -S && numactl --hardware

  2. Memory pressure monitoring:

    lsmem -s && free -h

  3. System inventory:

    echo "Memory Layout:" && lsmem -h

Output Formatting

  1. Specific columns:

    lsmem -o SIZE,STATE | column -t

  2. Summary with details:

    lsmem -s && echo "---" && lsmem

  3. Node-specific information:

    lsmem | awk '$6==0 {print}'  # Node 0 only