Database Develop

Using NAND as RAM?

After many tests I think that we really suffer from a lack of RAM. But the internal memory (NAND) should be the same speed as RAM I think. So why we don't use another 128Mb of NAND as additional RAM? A sort of swap part, but used as RAM and not as normal swap....
If someone related to the kernel would answer is it possible or not, it would be good)

DiMiK said:
After many tests I think that we really suffer from a lack of RAM. But the internal memory (NAND) should be the same speed as RAM I think. So why we don't use another 128Mb of NAND as additional RAM? A sort of swap part, but used as RAM and not as normal swap....
If someone related to the kernel would answer is it possible or not, it would be good)
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Using it as RAM would propably require major changes to the kernel if it is even possible which I doubt it is. Using it as swap would be the possible alternative and I pretty sure that is very possible and would help performance but at a cost.
1. You would either have very little left for system and data or you would have to put system and/or data on the SD-card and that alone may make you lose anything you gain from putting swap on NAND.
2. I actually asked the swap-on nand question myself and well, we can't replace our NAND, at least not easily and swap is I/O intensive and intesive I/O will sooner or later wear out the NAND. So basicly this is not a good alternative unless you want to turn your phone into a paperweight sooner than you had planned.
So what we can do is using compcache and/or swap on SD-card. The easiest thing is to just enable some compcache. It uses RAM as swap and uses compression on the contents so we can hold more things in RAM that we would usually be able to. This means Android can keep more apps in "sleep" allowing for faster switching between apps but it will also decrease the possible amount of available RAM for the active app. I usually turn on compcache with the default setting which is to use 25% of the RAM for compressed swap. It might be placebo but IMHO it feels a it "smoother" to use after that.
Another alternative is to use a swap partition in the sdcard. Just using swap means you do not need to load any compcache kernel modules and there is no compression taking place so it's a good alterantive. However you need know your way around partitioning SD-cards to get this running so it's not as easy as just enabling compcache (assuming the build supports compcache).
For the really advanced you can enable compcache with backing swap. It means it uses a certain amount of compressed swap i RAM and when it runs out of space there it starts putting stuff on the SD-card swap partition. Once again, a bit tricky to setup but may be the best alternative.
Read more about it here: http://wiki.cyanogenmod.com/index.php/Compcache

kallt_kaffe said:
I usually turn on compcache with the default setting which is to use 25% of the RAM for compressed swap. It might be placebo but IMHO it feels a it "smoother" to use after that.
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It make good effect: more applications can run simultaneously.

Compcache

Just curious, I've been flashing the latest nightlies and in the cyanogenmod settings I see 'use compcache'. I have it unchecked, any difference if I check it. I found a you tube video about 2 phones running with and without compcache. Compcache seemed to load pages better over time, but not initially. Any help would be much appreciated

Copied from this post on another thread..
Very roughly you have a finite amount of memory (RAM). When memory is accessed it is virtual addressing, so an application is given a piece of memory, but this isn't real RAM, the operating system manages this and maps it to where the data really is. Because of this system, the OS can give out more memory than is actually available. It can then store some of this memory on a storage medium and "swap" it with some other programmes memory when one is needed and the other isn't. This is how swap works.
With compcache, instead of storing the dormant memory on a hard disk it is compressed and stored in the RAM itself on a virtual disk. This takes up some RAM, but because it is compressed, more RAM is spare tha n if the data were left in memory as it is. Again this has the effect that more memory space can be handed out than the RAM that is really there.
Because Android manages applications so that when memory runs out it just closes applications running in the background, more applications can reside in the larger virtual memory space than before, making multi-tasking more pleasant and responsive.

I know that nfinitefx45 took compcache out of his latest builds in both the Stock and ZenHeroFX ROMs. I don't know all the technical reasons behind it, but I think it just didn't improve performance enough to be worth leaving it in. Granted those are Sense-based ROMs though which are generally a little slower and "bloatier" in nature than AOSP, so the performance difference maybe be greater in CM.

chromiumleaf said:
I know that nfinitefx45 took compcache out of his latest builds in both the Stock and ZenHeroFX ROMs. I don't know all the technical reasons behind it, but I think it just didn't improve performance enough to be worth leaving it in. Granted those are Sense-based ROMs though which are generally a little slower and "bloatier" in nature than AOSP, so the performance difference maybe be greater in CM.
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Thank you for the response, just wasn't sure. Since Darch left it unchecked, I figured I would ask

Swap partition for SGS ?

Hi again guys...
In Linux we have a SWAP partition for some time if RAM (Random Access Memory) will full OR for speed up applications by buffering in swap partition.
(Recommend Linux SWAP partition size: half of RAM)
so Android is Linux based and have kernel like Linux. Is it work to make a SWAP partition for SGS with swap file system?

You don't want that...
Android doesn't wipe RAM immediately anyway, so apps which are open and shutdown can be restarted again quickly (unless the RAM has been reused).
Also, apps on Android are designed to be shut down whenever free RAM runs out (its in the development guidelines that all applications should expect to be shut down at any time). Since most Android phones use high-speed NAND memory, when properly configured, apps load quicker too
The problem with swap is that it can lead to thrashing and loss of battery life. It's good for computers (because generally, you would rather lose performance and ensure you don't lose work), but on Android, applications should be killable at any time, and should have mechanisms to protect their work anyway.
It's probably possible to create a swap partition/file if you wish (try to swapon), but I foresee some potential side-effects, especially if you don't want to spend a lot of time managing memory manually.

i didn't think about battery life.
Thank you so muchhhhhhhhhh

I was actually exploring this option last night and stumbled that the kernel does allows swapon commands. I remembered trying it earlier on a stock rom but it was not available then.
Why I need the swap was because of the frequent shutdown of my launcher pro due to apps contenting for memory. The live wallpaper and heavy Widgets like pure messenger pro aren't helping much either, after much usage the device just slows down, lags and silently kills the background apps. The "minfree" settings were also tweaked but with much less desirable results was seen...
So I downloaded an app called "swapper2" from market and tested via 2 methods; Swap file and swap partition.
The performance of a swap file that sits in the NAND is not really that great. In fact it kinda lags me when memory is being swapped in and out of it. I think its the same problem with the i/o lag problems with any other rom
Then I tried a swap partition on my class 6 SD card. Although the lifespan of the card would be shortened and the battery life would be impacted, the performance is better compared to the earlier method.
In either method, the amont of apps that can be left opened at the foreground and background had increased and doesn't lag as more apps is being launched. Not bad for me but well, I guess it's all up to the user of the device at the end. Just my 2 cents...
I'll try the swap file method again over at the ext2 partition created by the lagfix and see how it goes next. Not sure if anyone interested though...
Sent from my GT-I9000 using XDA App

It seems that using the swap partition doesn't have the lag compared to using the swap file method.
It may be due to the I/O of multiple storage (parallelism ?) is better than a single storage or writing into the raw partition is better in terms of performance than a swap file.
I'm done with my findings, the device still have 60mb free and never lags, I'm sold.
Sent from my GT-I9000 using XDA App

What is meant by swap space?

Can anyone help me find, what is actually swap space means??

Swap space is a reserved space on a harddrive that acts as a "extended" RAM. When the RAM memory is full the kernel move stuff from the RAM memory to the Swap partition to free up memory. The data is later stored in the Swap until it's needed again.
The same thing or similar at least on a Windows pc is pagefile.
There are some discussions if swap files should be used or not on flash based storage devices since it increase the read/write cycles to the storage device and there by would break it faster (since flash based storage devices have a maximum of read/write cycles).

lintz said:
Swap space is a reserved space on a harddrive that acts as a "extended" RAM. When the RAM memory is full the kernel move stuff from the RAM memory to the Swap partition to free up memory. The data is later stored in the Swap until it's needed again.
The same thing or similar at least on a Windows pc is pagefile.
There are some discussions if swap files should be used or not on flash based storage devices since it increase the read/write cycles to the storage device and there by would break it faster (since flash based storage devices have a maximum of read/write cycles).
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wow..thats a good piece of information.thanks mate +1

W/O swap
When low memory occurs kernel kill processes
With Swap
Kernel move those about to be killed process to swap space and then map them pointer with RAM so when you open that app instead of allocating new memory to psycial RAM its been read from Swap and loaded to RAM.
As mentioned many times creating swap file and/or swap partition to flash drive aka our phone memory(internal storage) is not a wise choice cause recursive read and write can damage that nodes in longer run as flash memory has limited read/write cycles.
Other choice is to make swapfile and/or partition to external mmc but as external mmmc has which could also damage mmc in longer run but it could be replaced cheap rather than internal flash memory. Issue arises with external c swapfile and/or partition is slower read and write which could degrade performance
So one for-all if swap is needed than CompCache/Zram is a wise choice which uses physical reserved RAM portion for swap. Which uses extemsive CPU to compress data and write them to swap and retrive them by decompressing and writing back to physical RAM. Which is not harmful but can use more battery and obviously its faster than swap on external mmc. Usually its faster in the beginning and slight laggy after more hours and days usage
Sent from my LG-P990 using Tapatalk 2

spica1234 said:
W/O swap
When low memory occurs kernel kill processes
With Swap
Kernel move those about to be killed process to swap space and then map them pointer with RAM so when you open that app instead of allocating new memory to psycial RAM its been read from Swap and loaded to RAM.
As mentioned many times creating swap file and/or swap partition to flash drive aka our phone memory(internal storage) is not a wise choice cause recursive read and write can damage that nodes in longer run as flash memory has limited read/write cycles.
Other choice is to make swapfile and/or partition to external mmc but as external mmmc has which could also damage mmc in longer run but it could be replaced cheap rather than internal flash memory. Issue arises with external c swapfile and/or partition is slower read and write which could degrade performance
So one for-all if swap is needed than CompCache/Zram is a wise choice which uses physical reserved RAM portion for swap. Which uses extemsive CPU to compress data and write them to swap and retrive them by decompressing and writing back to physical RAM. Which is not harmful but can use more battery and obviously its faster than swap on external mmc. Usually its faster in the beginning and slight laggy after more hours and days usage
Sent from my LG-P990 using Tapatalk 2
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yh...this is actually what Iam looking for..thank you Spica it helped me a lot...So which is more harm less? swapfile,ZRam or CompCache?

basimsherif3 said:
yh...this is actually what Iam looking for..thank you Spica it helped me a lot...So which is more harm less? swapfile,ZRam or CompCache?
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Compcache or zram which is fastest amongst swap
Sent from my LG-P990 using Tapatalk 2

So in cm7, if compcache/zram is disabled, will it use swap?

aldyu said:
So in cm7, if compcache/zram is disabled, will it use swap?
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No untill and unless you have created swapfile and/or partition with an init.d startup script
Sent from my LG-P990 using Tapatalk 2

[TUTORIAL] Compcache and Swap

my 2c about compcache (now "zram") and swap
Both compcache and swap are used to improve performance AND maximum number of open apps.
1)How they work:
swap is the classic way to "increase" ram on a system.
Swap is a space on a non volatile memory (="not ram") where unused ram data are parked instead of being deleted.
Swap wears(and kills) memories it is put on. It is an heavy access file. Sdcards don't like it. They are not full-featured SSD Disks. Think of your photographs
Compcache is the new way to "increase" ram on a system,
compcache :
-reserves a part of you ram (cache),
-then it looks for unused data sitting on remaining, "real", ram,
-compresses these unused data (with a very primitive,loseless, algorithm) and
- send them to its cache OR to swapfile.
Compcache's trick works well when you have lots of higly,easily, compressable data in your ram. Text is higly compressable, an executable is less compressable.
1a)
-if, after compression , data are still "big" (compressed data > original data /2), then compcache sends compressed data to swap, not to cache.
-and when compcache is full, unused compressed data are sent to swap.
2) because of compression involved, compcache uses more cpu cycles than classic swap.
3) settings of both depends on
-hardware specs of the system.
-use of the system
4) compcache+swap is better than swap alone if your ram is filled with EASILY compressable data.
4a)Remember point 1a : compcache has a simple compression algorithm, and ALWAYS first compresses data.
AFTER COMPRESSION it decides if keeping them in cache or sending them to swap. This means that
if compcache has always to work with not compressable data, it will compress them AND send to swap. this means double work: compression AND swap access.
4b) First practical conclusion :
compcache is useful for people using LOTS of text-intensive apps (forums, webpages, docs, facebook)
compcache may be useful in apps using SIMPLE still images (some games, driving assistant)
compcache is useless in multimedia activity (watching youtube, movies, photographs, listening to mp3s, playing some other games.)
5) The swap file.
As told at the beginning, swap, both improve performance(=speed) AND number of apps simultaneously open.
Lets' take a look to the PERFORMANCE thing.
5a)On "classical" (fragmented, not-SSD hard disk) systems, a swap file is always faster than retrieving datas from original disk locations. EVEN IF the swap file is on the same disk where original datas are.
This happens mainly because :
5a1)-data in swap file are less fragmented, needing less seek time.
5a2)-swap file is usually put in the external (=fast) zone of an hard disk,
5b)On SSD systems (phones included) 5a1 and 5a2 are not true, and a swapfile is USELESS IN IMPROVING PERFORMANCE EACH TIME THAT it is keeping data which are already present on its same phisycal memory.
Examples :
5b1)opera browser executable is on phone memory; but Opera-cached-webpages have been moved on sdcard via app2sd.
In this situation a swap file on sdcard is obviously useless to improve internet browsing with Opera.
5b2) i use apps (facebook, Whatsapp) which DON'T have a good caching of their own. Swap could be useful: it could avoid re-downloading data from the internet.
Now, the INCREASE MAXIMUM NUMBER OF OPEN APPS argument.
This is always true.
So:
5c)swapfile on SSD speeds up multitasking ONLY IF you use apps that
-badly manage (or don't have) a cache of their own.
-don't like force closing
Since this seems to happen very often to android apps, a swapfile is useful.
5c1)Swapfile could speed multitasking also IF an app's well-designed-cache is on a media WAY SLOWER than swapfile (but this is not LG O2x situation: it has a class10 internal memory).
So, my 2 cents about "increasing" RAM in LG O2X is :
-leave apps on phone memory, and put swap on a class10 sdcard.
-enable compcache only if you use lots of text-rich apps.

First: I think this doesn't really fit into the development section.
Then: I can't second the post you made.
mercxda said:
Both compcache and swap are used to improve performance AND maximum number of open apps.
(...)
As told at the beginning, swap, both improve performance(=speed) AND number of apps simultaneously open.
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zRAM does NOT improve the speed of your device. Everything that's in the reserved zram storage will get compressed and decompressed, which takes some time (and cpu).
Swap is performing even worse. Instead of the fast RAM or the semi-fast compressed zRAM usage it's swapping onto the slow SD.
Sure, you can increase the maximum number of open apps, but the price is a lower performance.
So you're probably just meaning multitasking performance.
But still I can't agree to your conclusion:
mercxda said:
So, my 2 cents about "increasing" RAM in LG O2X is :
-leave apps on phone memory, and put swap on a class10 sdcard.
-enable compcache only if you use lots of text-rich apps.
Click to expand...
Click to collapse
As I wrote above zRAM is way faster than swap. So zRAM should be the first choice if you're running into low RAM situations.
If you still need more go and enable swap as well.
Last but not least:
Why are you talking about compache all the time? It's called zram nowadays, so call it that way.

tonyp said:
First: I think this doesn't really fit into the development section.
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First : thanks for your interest in this post . I partially agree with you: this post is on the borderline beetwen Q&A and Development, because swap is not a development matter, it's standard unix's way of working.
On the other side zram's use,way of working, and even its inclusion (or not) itself in default installs, is still under development.
https://lists.ubuntu.com/archives/ubuntu-devel-discuss/2012-December/014122.html
Sure, x86/x64 is not ARM. And CM is not ubuntu.
Then: I can't second the post you made.
zRAM does NOT improve the speed of your device. Everything that's in the reserved zram storage will get compressed and decompressed, which takes some time (and cpu).
Swap is performing even worse. Instead of the fast RAM or the semi-fast compressed zRAM usage it's swapping onto the slow SD.
Sure, you can increase the maximum number of open apps, but the price is a lower performance.
So you're probably just meaning multitasking performance.
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I, again , partially agree, i was fundamentally talking about multitasking performance. And sure, zram takes cpu cycles... I reserved a full, standalone point to say that.
But
i wouldn't be so sure about one being better than the other. My arguments are in the original post.
As I wrote above zRAM is way faster than swap. So zRAM should be the first choice if you're running into low RAM situations.
If you still need more go and enable swap as well.
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As I wrote, and argumented, before, compcache/zram is way faster in a way limited range of situations.
Last but not least:
Why are you talking about compache all the time? It's called zram nowadays, so call it that way.
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Because
1) I'm an old cat.
2) "Compcache" is a well chosen autodescriptive term.
3) It's been "compcache" for over 4/5 of it's life, and, well...
4) I'm an old cat. ;D
Have fun, and thanks for all your work in O2x developing.