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I've been using Ubuntu 11.10 for a while, but recently upgraded to a fresh install of 12.04 LTS. I am noticing a program called flush-encryptfs- using a significant portion (30 to 80%) cpu resources. It seems to start running when I launch chrome. If I close chrome, it will eventually stop. This is having a huge impact on system performance.

What is flush-encryptfs-? What is it doing? How can I stop it?

I am using an Asus Eee PC netbook. It's a new install of 12.04 with very few additional programs installed and yes I encrypted my home folder.

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I think you mean 'ecryptfs'. eCryptfs is a program for encrypting partitions and directories. Apparently encrypting your home folder takes quite some hit on your CPU performance.

I found it in general more useful to encrypt certain folders rather than the whole /home. /home contains a lot of configuration files that are accessed all the time by various programs, and each access makes ecryptfs work.

That said, I still find the CPU usage you report quite high.

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thanks. I misunderstood how the encrypted home directory operated. I thought it was decrypted when it was mounted, thus eliminating the need to decrypt "on the fly" as files were accessed. –  Michael Aug 23 '12 at 21:09

You're referring to a kernel thread that is created to write out dirty eCryptfs pages to disk (the kernel memory management bdi_forker_thread in mm/backing-dev.c does this).

Since these pages need to be encrypted this will indeed consume CPU cycles to complete. The amount of CPU consumed depends on the number of dirty pages to write, the speed of the output device and the speed and model of the CPU. Potentially it could consume 100% if the scheduler allows it to. It's a job that needs doing, so it uses available CPU cycles.

I generally only encrypt the data in my home directory that really needs encrypting (e.g. email, ssh keys etc) to limit the CPU consumption. I followed the instructions in the following wiki to just encrypt specific directories:

https://help.ubuntu.com/community/EncryptedPrivateDirectory

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Can you explain what you mean by "dirty" pages? –  Michael Aug 23 '12 at 21:01
    
A dirty page is one that has been modified and needs to be written back to disk at some point in the near future. –  Colin Ian King Nov 7 '12 at 23:54

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