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 Forum index » House Training » Users ( For the regulars )
Trying to Understand ZRAM
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Disco Makberto

Joined: 07 Aug 2011
Posts: 167

PostPosted: Wed 05 Mar 2014, 05:58    Post subject:  Trying to Understand ZRAM
Subject description: FKA Compcache
 

Hi, e-folks!

Please let me tell you that I am trying to understand this ZRAM for creating swap within RAM, but I can't, at least not fully. What I understand is that ZRAM creates a compressed swap within RAM, and that the coversion ration is 3:1, on average. Thus, let's say that I have a 512 MB RAM on my machine, and I am interested in creating a 768 MB swap. As the compression is 3:1, I need a 256 MB space of ZRAM for these 768 MB swap, or half of my original 512 MB. My question is, if I implement and decompress this ZRAM, what would be my total new RAM? Is it my decompressed ZRAM of 768 MB plus my original RAM of 512 MB for a total of 1280 MB? Or is it my decompressed ZRAM of 768 plus 256 MB (my unused original RAM) for a total of 1024 MB? It seems to me that the anwer is the latter, but I get confused when I read that the created block device (the ZRAM) can be used as general purpose ram or as swap.

Carlos Albert
D-Mak
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amigo

Joined: 02 Apr 2007
Posts: 2642

PostPosted: Wed 05 Mar 2014, 14:31    Post subject:  

1024 MB
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Disco Makberto

Joined: 07 Aug 2011
Posts: 167

PostPosted: Thu 06 Mar 2014, 06:48    Post subject:  

Thanks, amigo!

So, in a nutshell, in terms of total RAM, ZRAM is different than a normal swap. You see, in my scenario of a normal swap of 786 MB plus the original RAM of my machine of 512 MB, total RAM would be 1280 MB. However, if I apply the same but using ZRAM, that is, decompressed ZRAM of 786 MB plus what is left as original RAM (or half in this case) which is 256 MB, total RAM would be 1024 MB. Obviously, all things being equal, normal swap offers more space.

Now, the crucial questions. Up to now, I have been using a normal swap of 786 MB with my machine of 512 MB original RAM. This makes my system more or less stable. If I want to implement similar or better results using ZRAM, what would be better? A decompressed ZRAM of 786 MB ocupying 256 MB of my original 512 MB RAM for a total of 1024 MB RAM? Or something like decompressed ZRAM of 512 MB (rounded) occupying a third of my original RAM (170 MB RAM, rounded) for a total RAM of 854 MB (rounded)?

I am sorry for asking all of these, but I am sure the advice I can get would be useful not only for me but for other readers. The idea is to find the best amount of ZRAM for a machine of 512 MB original RAM. Any advice from members?

Carlos Albert
D-Mak
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gcmartin

Joined: 14 Oct 2005
Posts: 6730
Location: Earth

PostPosted: Thu 06 Mar 2014, 11:22    Post subject:  

To best help you, I think it appropriate to ask if you are running a non-RAM based PUP, say, from a CD or full-install? Reason: these would occupy and behave differently in the system than say a frugal or CD's pfix=ram,copy would. As such, this would impact available RAM for ZRAM use.

With only 512MB of RAM and the increased functionality that exist with many apps, I wonder (probably like you, too) if reducing available RAM to assist roll-in & roll-out speed (ZRAM Swapper) would be an actual benefit. One rationale is that ZRAM would reduce RAM available for system operations forcing much to time-slice in prioritization with that which resides in SWAP.

Good question, though.

Let us know from measurement what you find.

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Disco Makberto

Joined: 07 Aug 2011
Posts: 167

PostPosted: Sat 08 Mar 2014, 04:28    Post subject:  

Gcmartin says:

"With only 512MB of RAM and the increased functionality that exist with many apps, I wonder (probably like you, too) if reducing available RAM to assist roll-in & roll-out speed (ZRAM Swapper) would be an actual benefit."

D-Mak responds:

Spot on, gcmartin! With my system, I tried different amounts of ZRAM, namely 256 MB, 512 MB, 786 MB, and 1024 MB. I am not really satisfied with any of them. You see, while trying to watch VEVO videos, the smaller amount I went, the more the browser tended to drop; conversely, the greater amount I went, the more the browser tended to get frozen. If I had to choose one amount, I would probably go with 256 MB (or something like 384 MB) because, even if the browser drops, I can re-open it; on the other hand, if the browser gets frozen, my only option would be to turn off the system completely. One way or another, as I was saying previously, none of these solutions can be said to be optimum.

If I had 1 GB or more of actual RAM, perhaps ZRAM would help. However, in my situation of actual RAM of 512 MB, the benefit of ZRAM is dubious. By the way, I was using Puppy Lucid 5.25 via liveCD.

I hope this helps.

Carlos Albert
D-Mak
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