Linux – Keeping disk caches when hibernating

cachediskhibernatelinux

Is there a way to keep disk caches when hibernating Linux? I understand and agree that dropping them is the best option all-around. But my system is unresponsive after resume and I would like to give a try to keeping that data.

Of course, both hibernating and resuming will be slower, since disk cache data will have to be written to swap and restored. And, of course, I will need more swap space than I do now. But still, I've been looking all over the web and I haven't found any way to set things up like that.

I use pm-utils with uswsusp as backend, but I'm open to suggestions.

Best Answer

I know your pain, after hibernation my computer is much slower.

But there is another way. It's called TuxOnIce.

It is much faster than the in-kernel hibernation and it is able to save ALL the memory in use, including the disk caches. It makes a massive difference and actually makes hibernation in Linux usable on a day to day basis.

Beware - it does involve building your own kernel. If you're a Debian or Ubuntu user, this is fairly easy using kernel-package (make-kpkg). Good luck!

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Linux – Unresponsive desktop after resume from hibernation

You should check your swappiness value. Usually it is left at 60. It should be 10 or 15:

cat /proc/sys/vm/swappiness

You can change it on the fly with

sudo bash -c "echo -e 10 > /proc/sys/vm/swappiness"

and make it stick with

sudo bash -c "echo 'vm.swappiness = 15' >> /etc/sysctl.conf"

More information about swappiness can be found here: https://help.ubuntu.com/community/SwapFaq.

Linux – How and where is file system meta data cached in Linux

This is because your test is flawed. Running find . merely calls getdents() on the directory tree. A directory in this case is just a file that contains directory entries and is thus stored in page cache. Note you do nothing to actually access the files you are attempting to cache in this manner.

Your test is basically caching all the directories in the filesystem tree and nothing else.

Try your test giving find a harder task to do. Such as forcing it to call lstat for every file and you'll see a different behaviour.

In my test there are a million files in this directory.

[root@home test]# echo 3 >/proc/sys/vm/drop_caches 
[root@home test]# time find ./tmp -printf "%p %c\n" >/dev/null

real    0m16.443s
user    0m2.123s
sys 0m9.320s
[root@home test]# time find ./tmp -printf "%p %c\n" >/dev/null

real    0m2.704s
user    0m1.224s
sys 0m1.479s
[root@home test]# echo 1 >/proc/sys/vm/drop_caches 
[root@home test]# time find ./tmp -printf "%p %c\n" >/dev/null

real    0m3.791s
user    0m1.359s
sys 0m1.756s

Note in the last test it takes slightly longer, I imagine this is directly related to all the reading of the directory 'file' itself rather than because the dentry and inode cache does not exist.

Best Answer

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