Many sysadmins coming from Windows backgrounds often panic when they see low "free" memory in Linux. But Linux fundamentally handles memory differently - unused RAM is wasted RAM. The kernel aggressively caches files and data in spare memory to accelerate future operations through:

• Page cache (file contents)
• Inodes and directory entries
• Slab allocations (kernel objects)

# Typical memory breakdown
$ free -h
              total        used        free      shared  buff/cache   available
Mem:            62G         12G        800M        1.2G         49G         48G
Swap:          8.0G        1.3G        6.7G

While regular cache dropping isn't recommended, these scenarios justify it:

• Benchmarking storage performance: Clearing caches ensures fair tests
• Memory pressure investigations: Isolating true memory leaks
• Post-massive-file-operation cleanup: After processing terabytes of logs

Example when testing raw disk IO:

# 1. Drop caches
sync; echo 3 > /proc/sys/vm/drop_caches

# 2. Run benchmark
fio --name=test --ioengine=libaio --rw=read --bs=4k --numjobs=16 \
    --size=1G --runtime=60 --time_based --group_reporting

Forcing cache eviction has significant consequences:

Instead of cron jobs, consider these approaches:

1. Tune vm.vfs_cache_pressure:

   # Increase reclaim aggressiveness
   sysctl -w vm.vfs_cache_pressure=100

2. Use cgroups v2 for memory limits:

   # Create memory-limited cgroup
   mkdir /sys/fs/cgroup/testgroup
   echo "4G" > /sys/fs/cgroup/testgroup/memory.max

These metrics reveal whether your system benefits from caching:

# Cache hit rate (higher is better)
grep -E '^(Cached|Buffers)' /proc/meminfo
vmstat -s | grep "pages paged in"

# Detailed slab info
sudo slabtop -o | head -20

Linux aggressively uses available RAM for disk caching (page cache and dentry/inode caches) to improve performance. This is often misunderstood as "memory being wasted" when viewing tools like free -m showing low "free" memory.

$ free -h
              total        used        free      shared  buff/cache   available
Mem:           32G        5.2G        500M        1.3G         26G         25G

The /proc/sys/vm/drop_caches interface exists for specific debugging and performance testing scenarios:

• Measuring true disk performance without cache effects
• Benchmarking applications with cold caches
• Debugging memory pressure issues

In production environments, regularly dropping caches is generally unnecessary and can hurt performance. However, exceptions include:

# Good use case: Before running benchmarks
sync
echo 3 > /proc/sys/vm/drop_caches
./run_benchmark.sh

# Problematic use case: Scheduled daily cache drops
0 0 * * * root /usr/bin/sync && echo 3 > /proc/sys/vm/drop_caches

Instead of blindly dropping caches, monitor cache hit rates:

# Check page cache effectiveness
$ sar -B 1
Linux 5.4.0-135-generic (...)    03/01/2023  _x86_64_    (32 CPU)

12:00:01 AM  pgpgin/s pgpgout/s   fault/s  majflt/s  pgfree/s pgscank/s pgscand/s pgsteal/s    %vmeff
12:10:01 AM      0.00      0.00     38.71      0.00    127.42      0.00      0.00      0.00      0.00

For systems with genuine memory pressure, consider:

• Tuning swappiness: vm.swappiness = 10
• Using cgroups v2 memory limits
• Implementing proper memory monitoring

# Better than dropping caches: Adjust swappiness
echo 10 > /proc/sys/vm/swappiness

The Linux kernel's memory management is sophisticated enough to handle cache allocation without manual intervention. Regular cache dropping indicates either a misunderstanding of Linux memory management or a deeper system configuration issue that should be addressed properly.