Red Hat Bugzilla – Bug 451738
kcryptd I/O blockage using encrypted filesystem on LVM
Last modified: 2013-02-28 23:06:50 EST
Description of problem:
When using an encrypted filesystem on LVM, whether an encrypted PV or LV, the
kernel frequently blocks for long periods of time waiting for I/O. top shows
anywhere from 20% to 100% CPU time waiting for I/O. Affected processes freeze
for several seconds, up to a minute or more, waiting for even small disk
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. Install Fedora 9 to encrypted PV.
2. Use moderately disk intensive processes such as firefox, thunderbird or liferea.
Some disk operations take dozens of seconds to complete.
Disk operations should complete in a reasonable time.
Issue did not occur with Fedora 8. Help tracking this down would be greatly
this is likely another case of the 'firefox fsyncs too much' bug. (it calls
fsync every time it updates the history db - ie, each time you view a new page.
unfortunatly fsync on ext3 means 'write everything in memory out to disk, not
just the data from this process'.
There is commit in 2.6.26 kernel (adding cond_resched()) in dmcrypt code, which
should help in this situation.
(System still need wait for io to finish, but other running application should
be more responsible.)
cond_resched() call is in 2.6.26+ kernels, it should help in some situations.
There are still some situations when system will wait for IO - mainly if you have multiple LVs but only one encrypted PV...
closing this rahwide, there is already kernel with this patch.