- application creates a large number (~15,000/hour) of uniquely named files which are deleted after a certain time
- Only about ~5000 files exist at any given time
- The memory usage reported by free becomes very high
- Investigation shows that the kernel memory slab cache of dentry structures (called
dentry_cachein RHEL4 or RHEL5, called
dentryin RHEL6 or RHEL7) is the cause of high usage
- What will happen when the dentry_cache exhausts the available (cached/free) memory?
- Why are dentry objects not freed after deletion of the file? The process owner? Could there be a hidden recycle bin somewhere due to the java delete method?
- Can you explain the vfs_cache_pressure in more detail?
- What other means can we do to reduce the dentry_cache size?
- Can vm.drop_caches=2 be used? Is there a different/preferred method? How safe is it? Can we run this a cron job?
- Red Hat Enterprise Linux 4
- Red Hat Enterprise Linux 5
- Red Hat Enterprise Linux 6
Subscriber exclusive content
A Red Hat subscription provides unlimited access to our knowledgebase of over 48,000 articles and solutions.