RHEL6: kernel not freeing memory, increasing growth of size-192 and size-256 slabs, believed related to NFS, specifically nfs_alloc_fattr and nfs_alloc_fhandle

Solution Verified - Updated -


  • We've experienced a failure with one of our production machines. This machine was running RHEL6.3 with kernel 2.6.32-279.el6.x86_64. It has 48GB of RAM and 66GB of Swap.
  • Initially we were running on kernel 2.6.32-279.el6 but updated to 2.6.32-358.6.2.el6 and still see the problem
  • There were large number of processes running on the box and at some point in time we run out of both physical and virtual(swap) memory and oom killer kicked in.
  • After that box was very slow with load around 100 and constant swapping.
  • We've killed all the processes that were using significant amount of memory (>200MB) but this did not result in any significant release of memory. Even after killing most processes and switching to single user mode.
  • slabtop showed that sizes size-192, size-256 are using about 20GB each.
slabtop | grep -n 20 

 Active / Total Objects (% used)    : 206100532 / 207069757 (99.5%)
 Active / Total Slabs (% used)      : 12058828 / 12058901 (100.0%)
 Active / Total Caches (% used)     : 119 / 195 (61.0%)
 Active / Total Size (% used)       : 45136325.42K / 45252935.30K (99.7%)
 Minimum / Average / Maximum Object : 0.02K / 0.22K / 4096.00K

102813400 102813219  16%    0.19K 5140670       20  20562680K size-192          
102810420 102810092  16%    0.25K 6854028       15  27416112K size-256


  • Red Hat Enterprise Linux 6
    • kernels from at least 2.6.32-279.el6 and less than 2.6.32-358.23.2.el6
    • NFSv3 Client
    • automount
  • NFS Server: NetApp storage with NIS to do the automount

Subscriber exclusive content

A Red Hat subscription provides unlimited access to our knowledgebase, tools, and much more.

Current Customers and Partners

Log in for full access

Log In

New to Red Hat?

Learn more about Red Hat subscriptions

Using a Red Hat product through a public cloud?

How to access this content