[Arm-dev] Using zram-swap

Gordan Bobic gordan at redsleeve.org
Fri Oct 12 16:54:15 UTC 2018

Depends on his use case. The only way he is seeing 4-5:1 CR is if there are
a lot of 0-filled pages being swapped out (those just get thrown away
completely). Firefox is known to request tons of RAM this way, of which it
regularly ends up not using most.
On a more sane load, you will typically achieve about 2:1.

Realistically, if you have 1GB of RAM and give 512MB to zram, that gives
you about 512MB of uncompressed RAM and 1GB of somewhat slower compressed
RAM that is still way faster than swapping.

On Fri, Oct 12, 2018 at 5:46 PM Robert Moskowitz <rgm at htt-consult.com>

> It is now built into Fedora29-arm.  That is where Mark got the source and
> the systemd support.  Yes, earlier many just used it.  Now Fedora-arm is
> based on it.
> On the Fedora-arm list, Peter Robinson has said he is seeing 4-5 fold
> compression.  That means that if you use a factor of 2 and have a 1GB
> memory SOC, that is effectively 2.5GB ram.  Or use a factor of 4 for
> effectively 1.75GB and less 'swapping'.  So you can use your 1GB duo core
> system more effectively, even if you currently have swap on a HD or SSD
> sata or USB attached.
> On 10/12/18 12:25 PM, Gordan Bobic wrote:
> Because swapping to SD card is slow, swapping to zram is fast, and zram
> only takes about 1/2 of the RAM that it provides.
> It's basically RAM compression.
> It works and makes a positive difference, even without exceedingly slow
> storage.
> On Fri, Oct 12, 2018 at 5:16 PM Fred Gleason <fredg at paravelsystems.com>
> wrote:
>> On Oct 7, 2018, at 07:58, Robert Moskowitz <rgm at htt-consult.com> wrote:
>> I have very recently learned about zram-swap.  Fedora-29-arm is using
>> it.  It supposedly makes a considerable difference even over HD swap.
>> Since many (potential) users of Centos-arm do not have a ready HD,
>> perhaps we can switch the image from a physical partition to zram? Or at
>> least instructions to change to this on the wiki.
>> Not to be utterly naive, but why is swap required on such systems at all?
>> To take core RAM and repurpose it as swap would seem to vitiate the entire
>> point of having a virtual memory subsystem in the first place.
>> Cheers!
>> |----------------------------------------------------------------------|
>> | Frederick F. Gleason, Jr. |              Chief Developer             |
>> |                           |              Paravel Systems             |
>> |----------------------------------------------------------------------|
>> | Perfection is reached, not when there is no longer anything to add,  |
>> | but when there is no longer anything to take away.                   |
>> |                                    -- Antoine de Saint-Exupery       |
>> |----------------------------------------------------------------------|
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