Re: [gentoo-user] zram / compcache, anyone?

[Paul Hartman]

On Tue, Oct 18, 2011 at 12:53 AM, Florian Philipp <lists@×××××××××××.net> wrote:
> Am 18.10.2011 07:16, schrieb Paul Hartman:
>> On Wed, Oct 12, 2011 at 8:52 PM, Pandu Poluan <pandu@××××××.info> wrote:
>>> Just stumbled upon this blog:
>>>
>>> http://www.webupd8.org/2011/10/increased-performance-in-linux-with.html
>>>
>>> anyone got any experience with zram/compcache on Gentoo?
>>
>> I'm using zram in a gentoo server with only 256mb of RAM, only used
>> for a few weeks so far. It seems to work and the server hasn't crashed
>> yet. :) I have allocated 128MB of compressed swap (64x2, actually, to
>> theoretically utilize both CPU cores for compression at the same time)
>> followed by normal on-disk swap at lower priority. Usually my total
>> swap used is less than 128MB so the real disk swap is rarely touched.
>> It's difficult to say if there is any improved performance, but I
>> haven't experienced any slowdown, which occasionally I did when swap
>> became heavily used in the past. Keep in mind the 128MB zram is the
>> uncompressed size, so the actual amount of RAM used by this should be
>> much less, depending on contents of the swap. Some even recommend
>> using zram equal to the amount of RAM but that idea scares me.
>>
>> After enabling the CONFIG_ZRAM module in kernel 3.0.6, I did this:
>>
>> modprobe zram num_devices=2
>> echo $((64*1024*1024)) > /sys/block/zram0/disksize
>> echo 1 > /sys/block/zram0/reset
> # sleep 1
>> mkswap /dev/zram0
>> swapon -p 11 /dev/zram0
>>
>
> In my experience, it can be necessary to put a `sleep 1` between reset
> and mkswap because the /dev/zram0 disappears and reappears after the
> reset command.

Good to know, thanks. In my case I typed those commands manually, so
of course I didn't encounter any timing-related problem like that.

> Another remark: The kernel docs recommend using /bin/echo instead of
> echo because problems are reported as write errors and the echo builtin
> of bash doesn't check for that.

Also noted, thanks again.