zram, anyone have an opinion on this?

[utu]

@ Blacksimon

I can confirm your experience -so far- with Knoppix 6.7.1 & CeBIT 7.
And I'm flabbergasted.

However, I can't seem to get any combination of my apps to create any 'used' swap values.
I'm using your commands but asking for 3.1 Gb swap, having 3.6 Gb total and apps amounting to 1+ Gb.
Perhaps there's yet one more magic word necessary to enable the magic.

Also, in my case, I have 2 cpus, and probably should enable 2 swap files.
Let me know how you make out.

________________
Werner: we'd not be disturbed if you moved this thread out of this category.

[utu]

.
@ Blacksimon

Although I am surprised at how much infrastructure you have uncovered that is applicable to zram,
this may be more due to my absence of experience with any form of swap.

In this instance, I think we are at least missing a driver called zram, and/or perhaps a clue like zram.ko
indicating some source material.
Also, I can't see any evidence on /etc/fstab that speaks to swapping of any kind.

I expect we may have to wait for 7.0.1 for the rest of the material to appear.
I'd be pleased to have you show otherwise.

[Blacksimon]

Hello Utu,
thanks for your words but my experience comes from the fact that I like to understand how to improve system performance by using hardware and software available without having to invest any more money...
I like to fully understand how things work...

Anyway in your case if you have multiple cores (2 cpus), then using a single zram can be a bottleneck, so you need zram0 e zram1 (it's present in your /dev/ ??)

modprobe zram  num_devices=2   #On July 20th 2011, the zram driver in the linux 3.1 staging area was modified to use zram_num_devices as modprobe parameter
echo $((512*1024*1204)) > /sys/block/zram0/disksize   #Allocate 512MB to zram0
echo $((512*1024*1204)) > /sys/block/zram1/disksize   #Allocate 512MB to zram1
mkswap /dev/zram0
mkswap /dev/zram1
swapon -p 100 /dev/zram0
swapon -p 100 /dev/zram1

But beware, I have not tested anything right now, I just created a swap in ram. Now we need to see if it actually works. It 's likely to miss the module zram.ko as you have highlighted. I'm waiting 7.0.1 too.

Regards.

[utu]

.
@ Blacksimon

Surprise: zram capability is already in 6.7.1; it just
hasn't been advertized or automated. As you were beginning to suspect.

Here's how to simulate what's coming in Knoppix 7.0+:

1. Boot up Knoppix 6.7.1 with the cheatcode knoppix mem=512M
This simulates a 'small' amount of ram these days.

2. Establish a zram set-up using 3/4 the ram as zram:
echo $((384*1024*1024))>/sys/block/zram0/disksize
mkswap /dev/zram0
swapon -p 100 /dev/zram0

3. Bring in LibreOffice and IceWeasel
(without zram, my mem used would be about 807M with
just these two and lxterminal)

4. Switch from one to the other of these; when you switch,
give each something new to do.

5. Examine free from time to time.

6. Bring in some more programs, check free again.

[Blacksimon]

Hi Utu,
this makes me very pleased.
Now, all that remains is to check the effectiveness of zram to judge whether you have a real performance increase.
I'll try to test the system, making him work hard with Gimp, maybe applying some filters to high resolution images.
I will tell you.

[utu]

Since this new capability will be applicable to any amount of ram,
it would be handy to have some simple, generic test that would
demonstrate significant usage of zram in any given situation.

For example, I've got 4 Gb of ram, and my normal needs are met by
less than 1.5 Gb having everything available all the time.

Dumbing things down to make-believe I have 512M proves a point,
but not convincingly, to my mind.

Some algorithmic scheme of dd manipulation and Fibonacci series has
an elegant flavor to it, although dd can be dangerous.

Another scheme might be based on spawning several simultaneous virtual systems.

[Blacksimon]

I used a Netbook Acer Aspire One with 1GB RAM, 768MB of zram setting.
I stressed the system by opening a dozen pictures and move large files from one hard disk to another, while surfing the internet watching videos on Youtube.

Well I have not noticed any significant performance increase.

Perhaps it is wiser to let the system use the full 1GB of Ram automatically, and perhaps this is not the appropriate test.
I do not know ...

[utu]

@ Blacksimon

Performance 'increase' should be a measure of the difference between
swapping to hdd and swapping to zram.

If your Knoppix can handle everything you need with 1 Gb, then
zram in Knoppix 7 will stay out of the way and not affect performance
at all.

If you need more than 1 Gb, presumably your system will hang up
without zram, unless you have some other swap to save you.
This is where Knoppix's zram comes to the rescue. Not crashing
is the performance increase in this case.

Just trying to clarify things, hope this helps.

[Blacksimon]

Everything you say is correct
Taking the test again with 512MB of zram, I noticed the effective use of zram, and in my case not crashing is a really performance increase

root@Black:~# free
             total       used       free     shared    buffers     cached
Mem:       1018724    1006984      11740          0      65772     128280
-/+ buffers/cache:     812932     205792
Swap:       616444     321768     294676

[cvevans]

.
@ Blacksimon

... 2. Establish a zram set-up using 3/4 the ram as zram:
echo $((384*1024*1024))>/sys/block/zram0/disksize
mkswap /dev/zram0
swapon -p 100 /dev/zram0

3. Bring in LibreOffice and IceWeasel
(without zram, my mem used would be about 807M with
just these two and lxterminal)

4. Switch from one to the other of these; when you switch,
give each something new to do.

5. Examine free from time to time.

6. Bring in some more programs, check free again.

Can I use this to shrink the existing zram0 on K703?
Can I modprobe to add a second, smaller zram0? How?
I am concerned about running out of memory; I already see long pauses, especially when the system suddenly decided to put 1G into the empty zram swap.
What happens if I put 1G of .debs into the ramdisk? They are compressed; will I lose that 1G of RAM? Do I get it back if I swapoff /dev/zram0?
I have searched the web, so far with no details found.
Thanks