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

[Florian Philipp]

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.

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.

Regards,
Florian Philipp