Delete clean cache to free up memory on your slow Linux server, VPS

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Many Linux systems, servers and VPS’s run on low memory and over time you will see a degradation of speed and responsiveness. By default, Linux got excellent Memory Management and it knows when to clean up cache to free up enough Memory to execute the next command. However, saying that, more new features being added to Linux everyday and when you are playing games, running a Web Server, a Database (i.e. MySQL, PostgreSQL, MariaDB etc.), Network Storage (NAS / SAN ), you will see there’s a drop on speed and responsiveness. By deleting and cleaning pagecache, dentries and inodes related cache data from Memory, you can get free up some of your Memory (RAM) which then makes rest of system work bit faster. This article will show you 3 different options to delete and clean cache to free up memory on your slow Linux server and small VPS’s.

Contents 

• Using drop_caches to clean cache to free up memory
• Clean and dirty caches
  • Dirty Cache
  • Clean Cache
• Kernel options for dropping cache
• Three drop_caches options to clean caches
  • Option 1: Free pagecache
  • Option 2: Free dentries and inodes info
  • Option 3: Free the whole lot – pagecache, dentries and inodes
• When do you run drop_caches? Is it safe?
• WARNING / CAUTION
• Home users vs Servers
• Example scenarios
  • My Desktop
  • My server
• Use cron to drop caches regularly
  • Option 1: drop_caches using cron
  • Option 2: drop_caches using sysctl
  • Option 3: drop_caches using a bash script
  • Restart crond service
• Conclusion
  • Google+
  • Related

Using drop_caches to clean cache to free up memory

Starting Linux Kernel v2.6.16 ono we have a new mechanism to have the kernel drop the page cache and/or inode and dentry caches on command, which can help free up a lot of memory. However, before we do that, we need to discuss about clean and dirty caches.

Clean and dirty caches

When you run something on a Linux system or server, Kernel will try to cache the response for a period of time so that the next time the same request is made, instead of running a complex lookup in disk/process, it can just fetch that info directly from Memory/RAM and send back a response. This is one of the main reasons Linux systems are so much faster and responsive. Alternatively, Linux systems will store data/info in Memory first before writing it to disk. So it goes both ways. Ideally, the data in Disk/database should be the same in Memory. But when you’re playing games, or it’s a busy Linux server, there will be some delay before these two (disk-data and memory-data) can sync up.
Cleaning cache is easy. But in Linux we have what we call clean and dirty cache.Let’s have a quick look at the definition of these two types of caches and later I will discuss why they are important when you clean cache.

Dirty Cache

Dirty Cache refers to data which has not yet been committed to the database (or disk), and is currently held in computer memory. In short, the new/old data is available in Memory and it is different to what you have in database/disk.

Clean Cache

Clean cache refers to data which has been committed to database (or disk) and is currently held in computer memory. This is what we desire where everything is in sync.

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