lubuntu-qa team mailing list archive

["Joyce MARKOLL" <meets@xxxxxx>]

On Sat, 28 Sep 2013 11:58:37 +0200
Jörn Schönyan <joern.schoenyan@xxxxxx> wrote:

> Am 28.09.2013 11:31, schrieb Leszek Lesner:
> > Am 28.09.2013 11:03, schrieb Jörn Schönyan:
> >> There are freezes with ZRAM in Precise, too. I experience this both 
> >> with original stack/kernel and the enablement stack from Raring. 
> >> Sometimes while shutting down, sometimes after a long session or when 
> >> the RAM is "full". After disabling ZRAM, there are no problems at all.

> > As far as I know the Precise kernel is 3.2 so it should not be 
> > affected by the problem currently introduced by the 3.10.6 kernel. The 
> > same goes for raring which uses the 3.8 kernel. And I hope the ubuntu 
> > kernel devs did not port over the broken zram module from 3.10.6 to 
> > the raring kernel.
> > So there only might be two possibilities:
> > 1. Its another bug.
> > 2. Its not really freezing but just writing a whole lot of chunks to 
> > zram which causes the cpu to run at 100 % for a long time and making 
> > system usage unusable until the chunk is written to zram.

> I am not 100 percent sure, as it is not my own machine :-/ myself, I 
> haven't seen the freezes.

> > The second thing can happen when lots of memory needs to be compressed 
> > into ram and the cpu is not the fastest (single core for example). So 
> > basically more than 60% of ram needs to be compressed. This takes a 
> > longer time then and maybe halt user input for the time being.
> > So it would help if you could verify if thats the case for you and if 
> > it still halts when you give it some time to work. (not more than 10 
> > mins please :) If this is really the case there are ways to limit the 
> > ram that is available for compression (so limit it to 40% for example) 
> > or even tweak the swapping setting to set how big the chunks should be 
> > that are written to swap. (swap in this case made available from zram)

> The owner waited at least 5 minutes, if it will unfreeze. The notebook 
> is quite old, a Pentium M if I remember correct. It has 512 MB RAM and a 
> VIA graphics card which I first suspected to cause the freeze :-)


> > Also in rare occoasions(so if you only have 1 GB RAM and zram only 
> > gives you 250 MB of swapspace and you need more) it might be useful to 
> > use zram in combination with swap space on harddrive. So it would than 
> > first swap out to zram until its full and then write to swap on hd.
> > As for the shutdown issue this is exactly where it might come to an 
> > hold for some seconds as it needs to clean zram (swap space by zram is 
> > basically unmounted and the contents is written back to ram by swapd 
> > or at least it is trying to write as much as possible back to ram)
> Could be - I've set up a swap partition with 1,5 GB so this should in 
> theory not be an issue.
> 
> Jörn

Hi,

I have said what follows in other posts on this list lately, however I will repeat it:

I have used zram in Ubuntu 12 as well as in the present Lubuntu Saucy testing and I don't
meet with any freeze : I suspect your kernel(s) want to swap to disk which does cause
freezes.

Last year I installed antiX (based on Debian testing) on a very very old machine, HP
Omnibus with 192 MB ram and a 800 Mhz celeron processor : I had to configure the
swappiness to prevent the kernel from swapping to disk. Once done the zram module (and
the associated scripts) did a very good job.

Could you try where your distributions do "freeze" to ask the kernel to not swap to disk?
Here is a configuration file:
http://meets.free.fr/Downloads/BentoVillageProject/Configurations/System/etc/sysctl.d/50-local.conf

of course, it is meant to be added to /etc/sysctl.d

Else, I configure 20% or 25% max in the initramfs.conf file (under /etc/initramfs-tools)
ie: COMPCACHE_SIZE="20%"

(I have explained in another thread that 50%, which is the default in Ubuntu for a reason
which is unknown to me, might take too much from the CPU... and the above configuration
is what I have been using in several distributions since several years with success, as
well as a few dozens of users whom I provided with remixes having this setup).

Let me also add a word about the swap to disk : it is highly desirable to avoid swapping
to disk, because it is very slow compared to swap to ram and therefore likely to trigger
freezes.

You can find more information about zram here:
http://code.google.com/p/compcache/w/list

Regards,
Mélodie