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I've always run compcache on my ROMs when possible and I recently had the idea that setting the full amount of RAM to compcache could be an interesting test. The theory being that it may be slightly slower overall to have ramzswap compressing pages, but minfree would have heaps of memory to play with and apps would never quit, so multitasking would be faster as no apps are writing out to /data and then having to relaunch when I switch to them again.
I've set compcache with the init script like so
Code:
insmod /system/lib/compcache/ramzswap.ko;
rzscontrol /dev/block/ramzswap0 -i -d 98304;
busybox swapon /dev/block/ramzswap0;
And Linux reports the swap is working
Code:
# free
total used free shared buffers
Mem: 107332 105972 1360 0 8
Swap: 98296 48940 49356
Total: 205628 154912 50716
But no matter what I do, even if I launch a heap of apps, I can never get swap usage above the ~48Mb RAM seen here.
Furthermore, apps like Auto Killer and Free Memory only report I have 102Mb RAM total.
What's going on here? Why does Android think it only has 100Mb when free is reporting near on 200Mb total? Why does compcache only fill up halfway and no more? Does this mean that ~48Mb RAM is the "sweet spot" for compcache and any more is pointless?
The phone does feel faster when switching between apps but I could just be imagining it. Out of interest this is a 32B Magic running Dwang 1.17.1, which is basically just Donut AOSP with a faster framework and kernel.
Any ideas/help/suggestions would be appreciated?
Swap is never, ever, regarded by the system as real memory, hence why the system won't report it, since you really only have ~100 mb physical ram.
As to why you're only using 48, I believe that 48 is 1/2 96, so it probably means pages are being compressed 2:1, so the full memory is being compressed and dumped into RAM, and it only occupies 48 MB, leaving you 48 free for other processes.
Again, remember comcapche is swap, not real memory.
jubeh said:
Swap is never, ever, regarded by the system as real memory, hence why the system won't report it, since you really only have ~100 mb physical ram.
As to why you're only using 48, I believe that 48 is 1/2 96, so it probably means pages are being compressed 2:1, so the full memory is being compressed and dumped into RAM, and it only occupies 48 MB, leaving you 48 free for other processes.
Again, remember comcapche is swap, not real memory.
Click to expand...
Click to collapse
I don't think that that analysis is quite right....
First off, you MUST maintain SOME amount of real memory available... otherwise it'll crash in a spectacular way. I believe that the linux kernel itself may have a safety feature that maintains a certain minimum amount of physical ram available. There ARE certain things that the linux kernel will not be willing to swap, such as ITSELF.
Just imagine what would happen if the kernel swapped itself..... any attempt to do this wouldn't end well. Especially if it tried to swap its ENTIRE self since the kernel MUST be in memory in order for it to run.
There is also the swappiness setting... it controls the system's tendency to swap.
And finally, there is the possibility that you may simply not be starting enough processes to consume the full memory!
So imagine this; you have your compcache set for a certain size. It grows to that size and then finally, the kernel says "screw you, you can't have any more memory!" blows an error back to compcache, which complains back to the kernel "sorry, swap is screwed." Yep.... the kernel tells compcache which tells the kernel rather than the kernel just knowing.
You definitely don't want this happening.
Note: I can forsee some serious stability problems that this could result in related to the low memory process killer. Specifically, your compcache grows to its maximum allowed size, you start an application, the low memory process killer figures that you've got plenty of memory available, doesn't kill anything off, tries to start some application, crashes spectacularly when the kernel complains back that it doesn't have any memory. I don't know if this would happen with a stock low memory process killer, but definitely would with the swap hacks added....
lbcoder said:
Note: I can forsee some serious stability problems that this could result in related to the low memory process killer. Specifically, your compcache grows to its maximum allowed size, you start an application, the low memory process killer figures that you've got plenty of memory available, doesn't kill anything off, tries to start some application, crashes spectacularly when the kernel complains back that it doesn't have any memory. I don't know if this would happen with a stock low memory process killer, but definitely would with the swap hacks added....
Click to expand...
Click to collapse
92 MB of compcache doesn't really need 92MB of compcache... that's the point of being compcache.
Compcache file in RAM grows when cache gets stuffed inside compcache.
Setting a low swappiness will cause compcache to just swap what's needed.
And even with full compcache, in the end you end up having around 140 mb (or so) free ram. 92mb of compcache that takes like 50mb and 42 extra mb of normal ram.
I think this idea is great (I was just too lazy to try yet...). Instead of dalvik vm having to free up memory it can stuff some more mb in compcache. should be faster.
I didn't really think my post through... but I hope some of you understood some of the things I wanted to communicate xD
domenukk said:
92 MB of compcache doesn't really need 92MB of compcache... that's the point of being compcache.
Compcache file in RAM grows when cache gets stuffed inside compcache.
Setting a low swappiness will cause compcache to just swap what's needed.
And even with full compcache, in the end you end up having around 140 mb (or so) free ram. 92mb of compcache that takes like 50mb and 42 extra mb of normal ram.
I think this idea is great (I was just too lazy to try yet...). Instead of dalvik vm having to free up memory it can stuff some more mb in compcache. should be faster.
I didn't really think my post through... but I hope some of you understood some of the things I wanted to communicate xD
Click to expand...
Click to collapse
Interesting in theory, but if you actually read what I said, you would note that this is entirely IMPOSSIBLE and would crash spectacularly if not for and in some cases in SPITE of certain safety features built into the kernel.
Note: If you have 70 MB worth of data that CAN'T be swapped, that leaves 20 MB ***PEAK*** available to compcache.
It is neither fair nor sensible to think of all memory as being equal. Running processes ***MUST*** have REAL MEMORY.
A little off-topic, but this discussion (the possibility of REAL "compressed" memory) sparked a thought/question:
Would/could KSM* bring any benefit to Android? (Not sure if the KSM module can even compile/work on ARM)
I know KSM is normally used for detecting and sharing duplicate pages among KVM guests, but I wonder how many pages in a typical running Android installation are duplicated, and thus candidates for sharing/de-duplication.
*I can't posts links yet, so those that don't know what KSM is, will just have to google for it.
lbcoder said:
There ARE certain things that the linux kernel will not be willing to swap, such as ITSELF.
Click to expand...
Click to collapse
I was under the impression the kernel keeps itself in RAM and then reports free memory to the rest of the OS. This is why the phone physically has 192Mb RAM, but only reports 96Mb free (or 107Mb with RAM hack). Perhaps my understanding of Linux/Android memory reporting is not correct?
lbcoder said:
It is neither fair nor sensible to think of all memory as being equal. Running processes ***MUST*** have REAL MEMORY.
Click to expand...
Click to collapse
I think this is likely what is happening. Home, Phone, System and other processes with a low oom are refusing to swap out as they are still running. If the compcache allocation in RAM is dynamic as domenukk says, then those processes are occupying enough RAM that the ramzswap allocation can only grow to ~48Mb as I am seeing. I didn't think of this.
Nor have I tweaked swappiness. It's currently set to 60 (default) so I'd assume it's not too fussy with paging out. I will try playing with this at 10 and 100 to see if I can force anything more into swap or if it's less willing to swap.
brainbone said:
*I can't posts links yet, so those that don't know what KSM is, will just have to google for it.
Click to expand...
Click to collapse
I do not know either, but here are some links people may wish to look at
http://fedoraproject.org/wiki/Features/KSM
http://lwn.net/Articles/306704/
http://lwn.net/Articles/330589/
http://www.linux-kvm.com/content/using-ksm-kernel-samepage-merging-kvm
Ok I am not at all experienced in this area but this is just a suggestion. You say that you can only get 48mb of swap to be compressed at a time. If those 48mb were uncompressed, then that would occupy the 98mb you alloted to it. If you set the cc at say 128mb, then in (my) theory up to 64mb of it the actual ram would be used. I don't know how much sense I'm making but not sure exactly how to explain it. If you don't get it I'll try explaining my logic a little more in depth.
mejorguille said:
If you set the cc at say 128mb, then in (my) theory up to 64mb of it the actual ram would be used.
Click to expand...
Click to collapse
It appears you are right. Even with swappiness set to 100 and opening every app on my phone I'm not able to fill more than half of 128Mb compcache before minfree stats gracefully closing processes:
Code:
/opt/android-sdk-linux_86/tools$ ./adb shell free
total used free shared buffers
Mem: 107332 105956 1376 0 32
Swap: 131064 65520 65544
Total: 238396 171476 66920
Super Jamie said:
It appears you are right. Even with swappiness set to 100 and opening every app on my phone I'm not able to fill more than half of 128Mb compcache before minfree stats gracefully closing processes:
Code:
/opt/android-sdk-linux_86/tools$ ./adb shell free
total used free shared buffers
Mem: 107332 105956 1376 0 32
Swap: 131064 65520 65544
Total: 238396 171476 66920
Click to expand...
Click to collapse
I rock=p
So what's your performance like, compared to say 32mb cc or no cc at all?
It's different but I like it.
There is sometimes a slight (<2 second) pause when launching a new app (I assume this is compcache compressing old pages to swap to make way for the new app) however once the app is up and running, it almost never "exits" so switching between previously-launched apps is noticeably faster than without compcache. I run HelixLauncher Donut and it's never closed and re-launched while I've been trying this, however it did sometimes with 32Mb cc and quite often without cc at all.
I had 5 day uptime last week with 96Mb compcache (rebooted whilst testing another app for a friend) so I don't think stability is an issue. The CM wiki indicates performance with cc is better upon boot then gradually declines, even if that is the case, rebooting my phone once a week is no big issue.
Unless I run into any major issues, I'll be keeping my phone with large compcache
Super Jamie said:
I was under the impression the kernel keeps itself in RAM and then reports free memory to the rest of the OS. This is why the phone physically has 192Mb RAM, but only reports 96Mb free (or 107Mb with RAM hack). Perhaps my understanding of Linux/Android memory reporting is not correct?
I think this is likely what is happening. Home, Phone, System and other processes with a low oom are refusing to swap out as they are still running. If the compcache allocation in RAM is dynamic as domenukk says, then those processes are occupying enough RAM that the ramzswap allocation can only grow to ~48Mb as I am seeing. I didn't think of this.
Nor have I tweaked swappiness. It's currently set to 60 (default) so I'd assume it's not too fussy with paging out. I will try playing with this at 10 and 100 to see if I can force anything more into swap or if it's less willing to swap.
I do not know either, but here are some links people may wish to look at
http://fedoraproject.org/wiki/Features/KSM
http://lwn.net/Articles/306704/
http://lwn.net/Articles/330589/
http://www.linux-kvm.com/content/using-ksm-kernel-samepage-merging-kvm
Click to expand...
Click to collapse
ksm sound cool. As every app runs inside dalvik vm. Not sure though... somebody should ask cyanogen
I am happy thatlarge compcache works out so well for you.
BTW doesn't cyanogenmod 5 count the whole swap as real memory since test4 or so?
Oh and overclocking ondemand to as high as possible will speed up app opening and switching a lot while on compcache
domenukk said:
doesn't cyanogenmod 5 count the whole swap as real memory since test4 or so?
Click to expand...
Click to collapse
It's counted as available "swap" memory, but not "real" ram. Pages stored in "real" ram (memory that the cpu can directly execute code in) still need to be freed up (moved to swap) before previously swapped pages can be moved back in to "real" memory to be executed.
domenukk said:
ksm sound cool.
Click to expand...
Click to collapse
The beauty of KSM is that it does no "swapping". It simply combines 4KB pages that are identical -- so instead of two identical 4KB pages using 8KB of ram, they only take 4KB. The code is executed in place.
KSM would, however, still require swap. If at any time a virtual shared 4KB page is written to, it needs to be copied to a free page to avoid corrupting the virtual page it was a duplicate of before the write. Swap is needed to ensure that there will always be enough available free pages when this happens.
domenukk said:
As every app runs inside dalvik vm.
Click to expand...
Click to collapse
KSM is not dependent on a VM, but the existence of VMs (java or otherwise) increases the likelihood of duplicate pages.
domenukk said:
Not sure though... somebody should ask cyanogen
Click to expand...
Click to collapse
I'd certainly be interested in cyanogen's thoughts on this, but I'm sure there are others that would be able to chime in as well.
Relevant excerpt from kernel.org/doc/ols/2009/ols2009-pages-19-28.pdf
KSM and embedded
KSM is suitable to be run on embedded systems too; the important thing is not to register in KSM regions that won’t likely have equal pages. For each virtual page scanned, KSM has to allocate some rmap_item and tree_item, so while these allocations are fairly small, they can be noticeable if lots of virtual areas are scanned for no good.
Furthermore, these KSM internal rmap/tree data structures are not allocated in high memory. To avoid early out of memory conditions, it is especially important to limit the amount of lowmem allocated on highmem 32bit systems that might have more than 4GB of memory, but these shouldn’t fit in the embedded category in the first place.
Click to expand...
Click to collapse
Super Jamie said:
I was under the impression the kernel keeps itself in RAM and then reports free memory to the rest of the OS. This is why the phone physically has 192Mb RAM, but only reports 96Mb free (or 107Mb with RAM hack). Perhaps my understanding of Linux/Android memory reporting is not correct?
Click to expand...
Click to collapse
Memory reporting is a tricky thing.
But in general, when RAM is allocated to HARDWARE, it is NOT REPORTED.
The chunk of the 192 that is not reported is assigned PRIMARILY to the RADIO. Another chunk is assigned to the GPU. Still more is assigned to the AUDIO HARDWARE.
The part used by the kernel itself IS reported. The most trivial empirical evidence to prove this to you is that when you change KERNELS, it doesn't affect the total system memory, despite your KNOWING that different kernels use different amounts of RAM.
Another bit of empirical proof is that activating COMPCACHE does not reduce the total physical ram reported. And yes, COMPCACHE is part of the kernel...
Now here's another concept of crash and burn: IF everything in memory could be cached in compcache, then what would stop compcache from caching compcache in a horrible infinite memory sucking loop? That would be very very bad, LOL.
I think this is likely what is happening. Home, Phone, System and other processes with a low oom are refusing to swap out as they are still running. If the compcache allocation in RAM is dynamic as domenukk says, then those processes are occupying enough RAM that the ramzswap allocation can only grow to ~48Mb as I am seeing. I didn't think of this.
Click to expand...
Click to collapse
NOW you're getting the idea! Running processes, kernel, etc., all need physical RAM (though actually those processes you mention most definitely CAN be swapped...), and therefore you CAN'T make the ENTIRE RAM into compcache!
Nor have I tweaked swappiness. It's currently set to 60 (default) so I'd assume it's not too fussy with paging out. I will try playing with this at 10 and 100 to see if I can force anything more into swap or if it's less willing to swap.
Click to expand...
Click to collapse
Just beware of possible crash-and-burn
Super Jamie said:
It appears you are right. Even with swappiness set to 100 and opening every app on my phone I'm not able to fill more than half of 128Mb compcache before minfree stats gracefully closing processes:
Code:
/opt/android-sdk-linux_86/tools$ ./adb shell free
total used free shared buffers
Mem: 107332 105956 1376 0 32
Swap: 131064 65520 65544
Total: 238396 171476 66920
Click to expand...
Click to collapse
That doesn't actually follow from what you've posted here.
What follows is that 105956-(65520/2)=73196 of what occupies your memory can't be swapped (kernel, running processes, etc.).
lbcoder said:
What follows is that 105956-(65520/2)=73196 of what occupies your memory can't be swapped (kernel, running processes, etc.).
Click to expand...
Click to collapse
Do you know why swap constantly "settles" at almost exactly half usage regardless of what size compcache I set?
For example, I set 64Mb compcache yesterday and rebooted. Just using my phone normally (browser, genie widget, music) I have this:
Code:
total used free shared buffers
Swap: 63992 32096 31896
Does this mean I am effectively reducing the amount of RAM the phone has for the kernel, "foreground app", "visible app" and "secondary servers" (to use the minfree terms), whilst at the same time allowing more "hidden app" and lower processes to swap out instead of terminating gracefully?
This disturbs me
-------------------------------------
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brainbone said:
I'd certainly be interested in cyanogen's thoughts on this, but I'm sure there are others that would be able to chime in as well.
Click to expand...
Click to collapse
He doesn't know much about it, yet. But he seems inerested.
Attached a short conversation over #twitter
# Dominik domenuk
@cyanogen Is ksm any good 2 save RAM? probably not - you would have already done it http://lwn.net/Articles/329123/
# Steve Kondik cyanogen
@domenuk I don't know too much about it, I think its meant for sharing between distinct virtual machines
@domenuk it could have a lot of potential though
# Dominik domenuk
@cyanogen basically yes. But he states its also for normal apps. I have no idea to what extend android apps have similar memory, though...
# Steve Kondik cyanogen
@domenuk a lot, Android is all about IPC and shared memory. I wouldn't be surprised if the Dalvik people are thinking about it.
Click to expand...
Click to collapse
Here is a way to make Android use more than 50 percent of a swap partition. I am not sure how it will act with compcache... Should be the same... Run the following commands from a terminal or add them following to your userinit.sh file:
Code:
su
echo 80 > /proc/sys/vm/swappiness
echo 150 > /proc/sys/vm/vfs_cache_pressure
!!WARNING!! - Messing with VM settings can cause data loss and system instability... Not liable for damages...
Using the above the "free" output is:
Code:
total used free shared buffers
Mem: 97708 95168 2540 0 356
Swap: 125296 88756 36540
Total: 223004 183924 39080
While we are at it... If anyone is willing... they can try this as well:
echo 1 > /proc/sys/vm/oom_kill_allocating_task
Reference : Article to Linux Insight
Been having pretty good results with it...
Here is a link to the rest of the vm settings...
Linux Insight article listing vm settings
L8r
Can anyone direct me to a guide somewhere?
I'd like to make an ext partition? Or would I? Is Swapper 2 just as fast? Tradoffs? Anyone run into their sd card wearing out yet?
bueler?
The message you have entered is too short. Please lengthen your message to at least 10 characters.
The consensus seem to be "do not use" except as 'last resort', and only needed on phones with 256MB or less of mem.
I wrote this, and I am waiting for a technical review from some experts in this field.
http://forum.xda-developers.com/showthread.php?t=897823
kschang said:
The consensus seem to be "do not use" except as 'last resort', and only needed on phones with 256MB or less of mem.
I wrote this, and I am waiting for a technical review from some experts in this field.
http://forum.xda-developers.com/showthread.php?t=897823
Click to expand...
Click to collapse
I have 256MB ram
At the moment, Compcache is good enough, but I can't help but wonder how much better it could be with swap instead of Compcache.
edit: "For example, If you have a 256MB system (shows as 262MB due to 1024 vs. 1000 KB size difference) and have 130MB of apps and data/cache loaded, then that leaves about 130MB for the system to actually RUN programs. That sounds like a lot, but in reality that is not enough, since the system itself takes 50-80MB, and services will take up another 30-50MB, leaving almost nothing. "
quick review, you don't appear to be differentiating between RAM and Flash? Having more apps installed shouldn't increase RAM usage at all. Unless I gravely misunderstand the Android OS, if I install a new program, it resides in the system flash, not the RAM, until I run it, at which point it gets loaded to RAM. When the system needs memory and no swap or Compcache is in use, it writes the state of the application to the flash and removes it from RAM.
What the swap does is similar to what compcache does-- compresses apps that are currently in RAM, and moves them to the swap space. In the case of Compcache, this is in the RAM. But since you're compressing it, background apps don't take nearly as much RAM, and you get an app switching speedboost because the processor can uncompress the compcache'd program, "move" it to RAM, compress the currently running program in RAM, and "move" it to the compcache. Forgive me if you already said this, I can't read the entire thing at the moment.
As for swap, I'm not sure if the processor compresses before going to the hard swap file, I don't think that it does-- when android starts getting low on RAM, it moves what was in RAM, to the swap on the SD-card. Since it does this when the system is low on RAM, and not when the system runs out of RAM, you never notice it. Reading the app back from the SD card happens almost instantaneously, because the sd cards can be read from at a speed of at least 20MB/s, maybe more. When you're restoring an app to RAM, 20MB/s is plenty.
edit2: I'm sorry but this guide is too vague to be anything more than moderately informative. Comments like:
-"CompCache, or "compressed cache", is handled by the Linux kernel. It takes a portion of your memory, and use it as a cache space, but compressed. By using on-the-fly compression it is able to make your memory appear to be a bit larger than it actually is. However, the result is slower performance.
This is usually NOT tweakble without mod ROM such as Cyanogen Mod. The kernel also must support this feature, and not all do. This also slows your phone. "
-"...swap space by either creating a swap file or a swap partition. This adds a lot of read/write action to your SD card and may substantially decrease its usable life."
-"This really slows your phone."
People wouldn't be doing these things for no reason. Compcache does not "make your memory appear a bit larger", when it at least doubles the amount of usable RAM-- when you allocate 60MB, if you average 75% compression (I usually see between 65% and 80%), do you know how much RAM this effectively nets you? Over at least 60MB extra, usually about 80! So my phone goes from having 256MB ram to having 340 effectively. Having your processor overclocked minimizes any slowdown from the compression/decompression; I haven't noticed any slowdown, and having the "extra" RAM definitely has made my phone more able to multitask.
You basically discourage users from doing ANYTHING like swapping, compcaching, etc to their phone, saying it "slows it down" and "can substantially decrease your SD Card's life". My experience has been otherwise regarding slowing it down, and regarding the SD card, the only part that would actually go bad is the swap partition. If you put that at the end of the drive, when it goes bad, you'll know, and you can just move the partition back 300MB and put your 300MB swap there. We haven't heard of any users' cards going bad from this yet. Also, if you have a class 6+ SD Card, they implement wear leveling on the card, so you don't need to worry about wearing out any individual bits.
Sorry, I'm just not digging it.
rancur3p1c said:
I have 256MB ram
Click to expand...
Click to collapse
Me too, me too...
At the moment, Compcache is good enough, but I can't help but wonder how much better it could be with swap instead of Compcache.
Click to expand...
Click to collapse
So try it. With CM612, I have CompCache AND Swap (through Swapper2 / 128 MB) turned on. It slows down every once in a while but my programs don't crash any more.
edit: "For example, If you have a 256MB system (shows as 262MB due to 1024 vs. 1000 KB size difference) and have 130MB of apps and data/cache loaded, then that leaves about 130MB for the system to actually RUN programs. That sounds like a lot, but in reality that is not enough, since the system itself takes 50-80MB, and services will take up another 30-50MB, leaving almost nothing. "
quick review, you don't appear to be differentiating between RAM and Flash? Having more apps installed shouldn't increase RAM usage at all. Unless I gravely misunderstand the Android OS, if I install a new program, it resides in the system flash, not the RAM, until I run it, at which point it gets loaded to RAM. When the system needs memory and no swap or Compcache is in use, it writes the state of the application to the flash and removes it from RAM.
Click to expand...
Click to collapse
At first I thought the same way you did, until I started looking in "diskusage".
According to diskusage, there is no separate RAM. 256MB is 256MB. App storage is where everything goes, and what's left is used to load services and such. The numbers I added up matches. I have 256 MB phone. 100 is for apps, which leaves about 150-160. System itself takes 50-80 (acore, gapps, phone, system...) then add a few services and you're down to 30-40 MB free to actually run the programs. The numbers seem to match up to what's shown at the bottom of "Manage Services".
I know it's weird, but perusal of Android developers kit doesn't contradict this understanding.
What the swap does is similar to what compcache does-- compresses apps that are currently in RAM, and moves them to the swap space. In the case of Compcache, this is in the RAM. But since you're compressing it, background apps don't take nearly as much RAM, and you get an app switching speedboost because the processor can uncompress the compcache'd program, "move" it to RAM, compress the currently running program in RAM, and "move" it to the compcache. Forgive me if you already said this, I can't read the entire thing at the moment.
As for swap, I'm not sure if the processor compresses before going to the hard swap file, I don't think that it does-- when android starts getting low on RAM, it moves what was in RAM, to the swap on the SD-card. Since it does this when the system is low on RAM, and not when the system runs out of RAM, you never notice it. Reading the app back from the SD card happens almost instantaneously, because the sd cards can be read from at a speed of at least 20MB/s, maybe more. When you're restoring an app to RAM, 20MB/s is plenty.
edit2: I'm sorry but this guide is too vague to be anything more than moderately informative. Comments like:
-"CompCache, or "compressed cache", is handled by the Linux kernel. It takes a portion of your memory, and use it as a cache space, but compressed. By using on-the-fly compression it is able to make your memory appear to be a bit larger than it actually is. However, the result is slower performance.
This is usually NOT tweakble without mod ROM such as Cyanogen Mod. The kernel also must support this feature, and not all do. This also slows your phone. "
-"...swap space by either creating a swap file or a swap partition. This adds a lot of read/write action to your SD card and may substantially decrease its usable life."
-"This really slows your phone."
People wouldn't be doing these things for no reason. Compcache does not "make your memory appear a bit larger", when it at least doubles the amount of usable RAM-- when you allocate 60MB, if you average 75% compression (I usually see between 65% and 80%), do you know how much RAM this effectively nets you? Over at least 60MB extra, usually about 80! So my phone goes from having 256MB ram to having 340 effectively. Having your processor overclocked minimizes any slowdown from the compression/decompression; I haven't noticed any slowdown, and having the "extra" RAM definitely has made my phone more able to multitask.
Click to expand...
Click to collapse
It also seriously depends on your SD card. I've read reports on Phandroid that said class 6 or 8 microSD cards would provide almost lag-free swaps, but that's on a G1 (which is already a slow phone).
You basically discourage users from doing ANYTHING like swapping, compcaching, etc to their phone, saying it "slows it down" and "can substantially decrease your SD Card's life". My experience has been otherwise regarding slowing it down, and regarding the SD card, the only part that would actually go bad is the swap partition. If you put that at the end of the drive, when it goes bad, you'll know, and you can just move the partition back 300MB and put your 300MB swap there. We haven't heard of any users' cards going bad from this yet. Also, if you have a class 6+ SD Card, they implement wear leveling on the card, so you don't need to worry about wearing out any individual bits.
Sorry, I'm just not digging it.
Click to expand...
Click to collapse
Constantly reading and writing the file will cause that area to get much heavier use and eventually cause it to fail the bootup "checking SD card". The only question is how much life is taken away.
I am running my Droid on 24% CompCache AND 128MB Swap right now. Occasional lag but otherwise runs quite well. It's also overclocked to 1.2 GHz with P3Droid's kernel. So I do practice somewhat of what I preach...
so if I have 512MB of ROM, and 256MB of RAM, and I fill up my ROM with programs, how much RAM do I have?
I don't follow how what you said can be.
SD Card writes-- SanDisk guarantees theirs for 100K writes to any given sector...that's good enough for the swap to not be a problem in the near future IMHO.
let's put it this way...
Here's the specs of Moto Droid from Motorola itself (http://developer.motorola.com/products/droid/)
RAM 256 MB
FLASH ROM 512 MB
USER STORAGE AVAILABLE (MAX) 256 MB
So the REST of the ROM clearly is to hold the Android OS itself. The actual programs you can load for running? 256MB. That's app storage.
I've always wondered if there's a way to read the actual ROM contents and enumerate that... But that's for another topic.
Found this useful post: boot process of Android OS
http://www.androidenea.com/2009/06/android-boot-process-from-power-on.html
Furthermore, I noticed that the "built-in" apps (i.e. bloatware) are actually just stuff left in the "system" dir which can only be accessed with root permission. So they are NOT store in "ROM" per se, but more like "part of boot rom".
I have to find explanation on how an app is loaded, but that helps...
Aha, so that's the term they used... Application Lifecycle.
http://www.youtube.com/watch?v=ITfRuRkf2TM
Okay, I take back what I said. Apps are loaded into RAM, but HOW things are allocated wasn't that clear.
From what I understand, apps, when they are killed by system, some exit gracefully by writing their instance "state" (data and cache) to app storage. Some just exits.
Browser will write the URL, for example. When the browser is "resumed", the process is loaded, then the instance loads back the URL and it's as if nothing happened.
I'll have to revise the paper, AND I haven't figured out what to say about swap and compcache yet.
Made some corrections.
On 256MB machine, 30MB is used by deep system buffers (not part of OS), another 32 for OS cache, so about 190 or so is available the OS itself to load apps and services, and just the default gapps, system, phone, and so on is about 60MB. So a fresh clean phone should ahve no more than 120-130 MB free. If you load a couple apps with autostart services, it'll quickly drop below 50MB.
http://stackoverflow.com/questions/2298208/how-to-discover-memory-usage-of-my-application-in-android
Another piece of the puzzle... The numbers at the bottom of "Manage Services" is as explained below:
(quoting from http://android-developers.blogspot.com/2010/02/service-api-changes-starting-with.html )
"Finally, along the bottom of the screen are some obscure numbers. If you know how to interpret them, this gives you a lot of information on the memory status of your device:
* Avail: 38MB+114MB in 25 says that the device has 38MB of completely free (or likely used for unrequired caches) memory, and has another 114MB of available memory in 25 background processes it can kill at any time.
* Other: 32MB in 3 says that the device has 32MB of unavailable memory in 3 unkillable processes (that is, processes that are currently considered to be foreground and must be kept running)"
The order is reversed in Android OS 2.2. Mine says
Other: 75MB in 5 Avail: 18MB + 20 MB in 3
Which should mean 75MB in 5 unterminable tasks, 18 MB free (or can be freed easily), plus another 20 MB used by 3 processes that can be killed to free up.
ProCrank says...
39911K System_server
15756K acore
12982K swiftkey
10136K DIY Screensaver (lock screen)
9392K Phone (system)
9093K ATKfroyo
6834K Terminal
3984K JuiceDefender
3785K Screebl
3482K system MMS
3329 SeePU
3244K Bluetooth
3199K SetCPU
1979K Zygote (which is Dalvik init)
1425K Mediaserver
and the rest is native system code well under 1MB in size.
If you add System_server, Phone, Zygote, Acore, and foreground app (terminal and procrank) you get about 75MB. It would be nice if that screen TELLS you which program it considers to be unterminable, but, oh well...
I had a search about and really I am only looking for confirmation as to whether this is accurate or not...
CALIBAN666 said:
I think its better to Post this here,when its not better,than sorry!!!
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Once a brief statement for those who are not traveling so long in the Android scene:
ZRAM = ramzswap = Compcache
In order to explain more precisely ZRAM first need other terms are more clearly defined:
Swap can be compared with the swap file on Windows. If the memory (RAM) to complete the PC the data that are being used not actively outsource (eg background applications) so as to re-evacuate RAM free. To this data is written to a hard disk. If required, this data is then read back from there easily. Even the fastest SSD is slower than the RAM. On Android, there is no swap!
In ZRAM unnecessary storage resources are compressed and then moved to a reserved area in the fixed RAM (ZRAM). So a kind of swap in memory.
This Ram is more free because the data then only about 1/4 of the former storage requirements have. However, the CPU has to work in more because they compress the data has (or unpack again when they are needed). The advantage clearly lies in the speed. Since the swap partition in RAM is much faster than this is a swap partition on a hard drive.
In itself a great thing. But Android does not have a swap partition, and therefore brings Android ZRAM under no performance gain as would be the case with a normal PC.
In normal PC would look like this:
Swap = swap file (on disk) -> Slow
ZRAM (swap in RAM) -> Faster than swap
RAM -> Quick
With Android, there is no swap partition, and therefore brings ZRAM also no performance boost.
The only thing that brings ZRAM is "more" RAM. Compressed by the "enlarged" so to speak of the available memory. That's on devices with little RAM (<256MB) also pretty useful. The S2 has 1GB but the rich, and more than. There must not be artificially pushed up to 1.5 GB.
After you activate the ZRAM also has 2 disadvantages. The encoding and decoding using CPU time, which in turn has higher power consumption.
Roughly one can say (For devices with more than 512MB RAM):
Without ZRAM: + CPU Performance | + Battery | RAM
With ZRAM: CPU Performance |-Battery | + RAM
For devices with too little RAM so it makes perfect sense. But who shoots the S2 already be fully complete RAM and then still need more?
Check whether you can ZRAM runs in the terminal with
free or cat / proc / meminfo
I hope it helps to understand zRam!!!!
Click to expand...
Click to collapse
Taken from here
That looks accurate, but it's a little hard to understand. A basic explanantion of zRAM is that zRAM compresses an actual block of RAM in order to have more RAM available to the system. If you make the compression too high with zRAM then your device will actually go slower as a result. An example of going over the top would be adding 256MB of RAM using zRAM on a phone that only has 768MB RAM (that's almost a 50% compression rate because ~600MB is available to the user). zRAM also requires the CPU to compress and decompress the data.
Zram is not ram. It is a virtual memory, also known as swap space, which lives in the ram. Virtual memory is the part where the system stores memory fragments which are not accessed, making more room for apps to store information in the ram. Most Pcs work with virtual memory on disk, but Linux has a zram feature, aka CompCache, which can hold unused pages in a compressed manner in memory, thus makes more ram available by compressing unaccessed pages.
Sent from my HTC Sensation Z710e using xda premium
so this ZRAM tweak is only useful for devices with low RAM's isn't it? well thanks for the info i dont wanna sacrifice batt life for some unnoticeable effect on my s3
once zram is enabled ....how do u remove the partition completely from.the ram after disabling it?
I noticed that my galaxy s duos comes with zram . However I wish to disable the partition and instead use swap partition in /cache .
So....how do I completely remove the partition space in ram?
Thank you .
Virtual Memory
Raven2k said:
Zram is not ram. It is a virtual memory, also known as swap space, which lives in the ram. Virtual memory is the part where the system stores memory fragments which are not accessed, making more room for apps to store information in the ram. Most Pcs work with virtual memory on disk, but Linux has a zram feature, aka CompCache, which can hold unused pages in a compressed manner in memory, thus makes more ram available by compressing unaccessed pages.
Sent from my HTC Sensation Z710e using xda premium
Click to expand...
Click to collapse
Sorry but you have a wrong concept of "Virtual Memory".
Google "virtual memory wiki" for the full article.
All programs have access only to their own "virtual" memory space of 4GB on 32bit OS'
But internally to the OS, that full virtual address space is divided on pages of 4KB each.
The OS manages all programs pages, if not enought RAM is available, it starts writing pages to the Page File / Swap partition.
When a program tries to read or write from its virtual memory address which page is not on physical memory, the OS launches a Page Fault Exception, takes over execution and reads the faulty page from storage (page file or swap partition) to physical memory, and if necessary writes another page to storage to make room for the requested page. Then it resumes the program execution.
From the article. Android does not have a Swap partition, but it compresses pages to ZRAM.
geno83 said:
Sorry but you have a wrong concept of "Virtual Memory".
Google "virtual memory wiki" for the full article.
All programs have access only to their own "virtual" memory space of 4GB on 32bit OS'
But internally to the OS, that full virtual address space is divided on pages of 4KB each.
The OS manages all programs pages, if not enought RAM is available, it starts writing pages to the Page File / Swap partition.
When a program tries to read or write from its virtual memory address which page is not on physical memory, the OS launches a Page Fault Exception, takes over execution and reads the faulty page from storage (page file or swap partition) to physical memory, and if necessary writes another page to storage to make room for the requested page. Then it resumes the program execution.
From the article. Android does not have a Swap partition, but it compresses pages to ZRAM.
Click to expand...
Click to collapse
True but not completely.
Android doesn't require ZRAM nor swap to work. It is a linux fraction but it doesn't act like linux completely.
Could anybody tell me the best way to improve ram efficiency without sacrificing batt
Thread cleaned. Either post relevant replies or don't post.
Right now, I have a full ZRAM. How does RAM handles it?
Sent from my Moto G4 Plus using XDA Labs
I wanted to know if we can increase the ram of our little pico (htc Explorer)....also I wanted to know the advantages of swap partition.....Does it increase the ram size ?? And also I wanted to know that if there are any other advantages of Sd-ext partition other than increasing the Internal memory ??
ahmadmemon said:
I wanted to know if we can increase the ram of our little pico (htc Explorer)....also I wanted to know the advantages of swap partition.....Does it increase the ram size ?? And also I wanted to know that if there are any other advantages of Sd-ext partition other than increasing the Internal memory ??
Click to expand...
Click to collapse
No, you can't. Physical RAM is fixed.
Swap acts as pagefile on Windows, if you know pagefile. swap is virtual RAM. When the system needs more memory, a part of RAM will be written to the swap partition. Swap partition is part of SD card, so it would be painfully slow to use. Beside that, using swap also quickly wear out your SD card.
Sd-ext partition can be configured to accommodate swap, if you have the right app/script. Normally, you divide your SD card in to 3 partitions, 1st for media, 2nd for app storage, 3rd for swap. And our phone's recovery have option to do this too.
As I said, I strongly object against using swap partition. It will make your phone even slower than without it.
Your best bet here is zRAM, or compcache. You can find zRAM setting in most CM based ROM. zRAM relies on compression to increase the virtual size of your RAM. For example, an app that usually takes 10MB of RAM will now take only 9MB if you choose 10% compression.
There're 10%, 18%, and 26% options. But zRAM is not free. It uses your CPU to compress and decompress data, so our phone's weak CPU is not very happy with it. Your choice. But if you really need more app to cache more app (better multi-tasking), 10% zRAM will give you about 40MB RAM more (400MB*10%=40MB), at the cost of little CPU and battery. Using 18% and 26% seems too aggressive.
redguardsoldier said:
No, you can't. Physical RAM is fixed.
Swap acts as pagefile on Windows, if you know pagefile. swap is virtual RAM. When the system needs more memory, a part of RAM will be written to the swap partition. Swap partition is part of SD card, so it would be painfully slow to use. Beside that, using swap also quickly wear out your SD card.
Sd-ext partition can be configured to accommodate swap, if you have the right app/script. Normally, you divide your SD card in to 3 partitions, 1st for media, 2nd for app storage, 3rd for swap. And our phone's recovery have option to do this too.
As I said, I strongly object against using swap partition. It will make your phone even slower than without it.
Your best bet here is zRAM, or compcache. You can find zRAM setting in most CM based ROM. zRAM relies on compression to increase the virtual size of your RAM. For example, an app that usually takes 10MB of RAM will now take only 9MB if you choose 10% compression.
There're 10%, 18%, and 26% options. But zRAM is not free. It uses your CPU to compress and decompress data, so our phone's weak CPU is not very happy with it. Your choice. But if you really need more app to cache more app (better multi-tasking), 10% zRAM will give you about 40MB RAM more (400MB*10%=40MB), at the cost of little CPU and battery. Using 18% and 26% seems too aggressive.
Click to expand...
Click to collapse
Does zRAM works without swap partition ??
Yes, it's different, you can read @redguardsoldier's post again, to get exactly what he is saying, just to be on the safe side
Increase RAM In HTC Pico (I worked For ME ).
ahmadmemon said:
I wanted to know if we can increase the ram of our little pico (htc Explorer)....also I wanted to know the advantages of swap partition.....Does it increase the ram size ?? And also I wanted to know that if there are any other advantages of Sd-ext partition other than increasing the Internal memory ??
Click to expand...
Click to collapse
TRY THE LINK BELOW IT WOKED FOR ME :laugh: >>>>>>>>>>>>
http://forum.xda-developers.com/showthread.php?t=2735281
I hope It will work for u as WELL :good:
I have heard of swapping storage on your phone for creating virtual ram, but I am curious and will be happy to know if you can also swap part of your phone storage space for virtual cpu. Is there even anything like virtual cpu?
You at any time can create virtual memory ( SWAP ) on a rooted Android OS to be used by Android OS.
Code example:
Code:
dd if=/dev/zero of=/data/local/swapfile bs=1024 count=65536
Side remarks:
CPU and RAM are totally different hardware components: CPU fetches program code from RAM, processes it, and returns result into RAM.
A SWAP doesn't increase device's RAM, you can't create a virtual CPU: a virtual CPU only exists on Anfroid emulators, not on any real Android device.
An Android device, as every computer, too, has a distinct amount of RAM .You may use SWAP, which stores the data actually residing in RAM on disk, if you run out of RAM .
SWAP can be / is useful because applications that aren't being used can be stored on disk until they are used. Then they can be "paged in" and run normally again. While it is not in RAM, though, the OS can use that RAM for something else, like disk cache. So it's a very useful feature, but if you don't have enough RAM to run your program, you definitely need more memory.
SWAP because it's part of the device's storage space is naturally much slower, which results in performance losses.
On Android each app is allowed to use only a certain amount of bytes of heap. This value is preset by app developer.
Thanks a lot.!