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I was thinking the other day about people opinions about using swaps and what the swappiness should be set to. I thought about how at sometimes during heavy use a higher swappiness would help while at other times it could slow things down. I was wondering if it would be possible to make a "smart" Swapper app that ran in the background and automatically adjusted the swappiness according to how much free memory is needed. For example when the phone is idle in your pocket swappiness would be at 10 but then as your started to browse the web or use GPS it would increase swappiness to allow you to have more free memory. Feel free to tell me why this is not practical or possible, it was just a thought I had.
I don't this its a case of being impossible
the question is why?
if your phone is 'sleeping' it probably isn't doing much with swap, so reducing swappiness won't achieve anything.
increasing swappiness when your phone comes to some load threshold will only increase the 'load' on swap as all of a sudden you want to dump more stuff from real memory into swap
tbh I don't understand why so many are obsessed with swap.
my advice , keep swappiness at default, and as for size of swap, large
why large?
good question, as you never really fill more than 40mb..
the reason for 'large' is 'wear levelling' your swap takes a hammering, if this partition is large then each block is going to have less writes on it than a smaller swap partition over a given period of time, thus increasing the life span of your sd card.
Agreed, playing with swappiness doesn't really help a whole lot.
One of the bigger issues (imo) is how once you have swap turned on the kernel will swap inactive pages out in order to make room for IO caching. If your device is sleeping, a lot of pages are suddenly inactive.
While at first it might seem like you'd want the ram to make up for a slow SD card, swapping out to the same device in order to make room for cache is counterintuitive. Unfortunately there is no way to cap the total amount of ram that can be used for cache. The logic is that unused ram and inactive pages can be put to better use to speed up IO.....except on devices with extremely limited ram and IO like most smartphones.
It's pretty unlikely that anything like that will make it back into the linux kernel any time soon. :\
Then again you never know Lunix is open sourced as well as android anything is possible
The idea is correct, but as said, it isn't possible. Don't count on any linux changes in the future on this. On the other hand, i think there is a possibility, but this should be calculated.
Swapiness is set on boot, right? If i change it when running my phone, would this make any difference on further use?
Now my suggestion is, find out what swapiness is ideal. When the program can calculate the ideal swapiness level, based on how much RAM is used over time, this would be nice? It would write this level down in a userinit, and when you reboot the phone, it would use this level as a reference point on swapiness.
Only downside is that you can't figure out the ideal swapiness, it depends on the phone, apps and personal preference.
Anyone has comments on this idea?
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.
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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've been seeing This CM7 and wanted to know what this was?!
I'm always reading how people say that xxMB is the best size.
But what is it? And how it works?
What's it for? What's the right size for a Galaxy S?
VeryCoolAlan said:
I've been seeing This CM7 and wanted to know what this was?!
I'm always reading how people say that xxMB is the best size.
But what is it? And how it works?
What's it for? What's the right size for a Galaxy S?
Click to expand...
Click to collapse
This setting is simply the maximum amount of heap space (read: memory) a single instance of the Dalvik VM (read: application) can obtain.
Don't read anything into the "benchmarks" performed. This setting should have little effect on overall system performance. The only scenario where it would be beneficial to increase the maximum heap size would be if you have an application that is very close to using up all of its available heap space, which would force it to run garbage collection frequently, which would use up CPU cycles. It is possible that lowering the maximum heap size could be beneficial in that it might prevent an application from obtaining more memory than it needs (by forcing it to garbage collect sooner), but that all depends on how the Dalvik VM is implemented and is really beyond my knowledge.
The heap (in Java) stores dynamically allocated variables, such as objects. Like Rueben_ said, when the heap is running low on memory, the JVM will run garbage collection. Garbage collection uses processing cycles, which will slow down your phone. In case you're wondering, the other place in memory where things are stored is called the stack, which stores arguments and parameters.
Oh okay
So how do you how much memory to put it for at Max?
Sent from my SGH-T959 using xda premium
mrinehart93 said:
In case you're wondering, the other place in memory where things are stored is called the stack, which stores arguments and parameters.
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I do believe the stack is reserved for storage of CPU data (typically, the contents of its registers) before it switches toanother context (or thread, which means loading a different set of data in its registers).
The memory zone where data from user apps (and the Dalvik VM is one of those, albeit a über-app of sorts since it runs all the other apps) is stored is rather just called "the heap". At least that's the way I learned it
daxdax89 said:
So is it better to put higher or lower heap size for games?
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Click to collapse
There is no right answer for this as you should have gathered from reading the answers you were given.
It all depends on how you use your phone.
Try out different settings with games and you'll see which suits your usage best.
Go on - Live on the edge a little lol...
daxdax89 said:
So is it better to put higher or lower heap size for games?
Click to expand...
Click to collapse
For the Vibrant if you use big apps then put the VM at like 128 or or something like that.
If you have small flashlight apps then use it at 32-96
Sent from my SAMSUNG-SGH-I747 using xda premium
Say, this seems to be a "magic bullet" for devices with modest memory sizes to keep apps from swamping the available memory. For my 1 GB Lollipop device, setting dalvik.vm.heapsize to "96m" improved the performance of the device. I was able to cycle between many memory-heavy applications without getting bogged down.
Be careful! Forgetting the "m" at the end, or setting the number too low will send your device into an endless garbage-collection, essentially locking you out. I set it too low myself, had to pop the battery, then quickly raise the value after reboot (before the "system_server" app got itself above the limit I had set), rebooting again to apply the new value. For a fair indication of a lower limit, look at the memory consumption of the "system_server" app. Set it above that to give it some headroom. Make sure you have a recovery plan before messing with this value!
This may be a general question for all android devices or not but I was curious about adding swap space to this device. It has 1 gig of ram and many may consider that to be enough, and it might be. I have cyanogenmod 10.2 installed and tried to enable zram, 10% seems to be the best setting as anthing higher caused a game to pop up a notice saying something about low memory and defaulting to lower values. When I checked to see if zram was used however it turns out it was, about 25mb - 34mb after booting. The issue with zram is when multitasking with lecturenotes and moonreader, The tablet would reboot and my notebook that was open in lecturenotes would be missing notes I took or the settings would be greatly messed up, or both. This was with 10%.
I am thinking since it was used, it might be helpful to have an sd card for this reason, to aid in multitasking. This is important to me because I run several apps at once (I wish cyanogenmod had multi windows, and google wouldn't threaten over it). So the question is will there be a benifit to buying an sd card on ebay (class 10 of course) and using it as swap space. It seems this tablet might be on the cusp of the memory being enough. Also I am thinking this might help to future proof it a bit when updating to newer releases of gyanogenmod. The sd card I was thinking of is 4 gigs and may plan on having 1gb swap space (this tablet is for school and other work). The tablet has 32gb storage and that is more than enough for me (I am only using 3gb of space) so I wont need to add anymore storage.
I should also add that when multitasking without zram enabled, the tablet reboots less but still has done it, and so far nothing has been lost in my notebooks. I am thinking that the memory of 1gb is starting to reach its limit, with no apps running I am consuming about 600mbs of it.
vanquishedangel said:
This may be a general question for all android devices or not but I was curious about adding swap space to this device. It has 1 gig of ram and many may consider that to be enough, and it might be. I have cyanogenmod 10.2 installed and tried to enable zram, 10% seems to be the best setting as anthing higher caused a game to pop up a notice saying something about low memory and defaulting to lower values. When I checked to see if zram was used however it turns out it was, about 25mb - 34mb after booting. The issue with zram is when multitasking with lecturenotes and moonreader, The tablet would reboot and my notebook that was open in lecturenotes would be missing notes I took or the settings would be greatly messed up, or both. This was with 10%.
I am thinking since it was used, it might be helpful to have an sd card for this reason, to aid in multitasking. This is important to me because I run several apps at once (I wish cyanogenmod had multi windows, and google wouldn't threaten over it). So the question is will there be a benifit to buying an sd card on ebay (class 10 of course) and using it as swap space. It seems this tablet might be on the cusp of the memory being enough. Also I am thinking this might help to future proof it a bit when updating to newer releases of gyanogenmod. The sd card I was thinking of is 4 gigs and may plan on having 1gb swap space (this tablet is for school and other work). The tablet has 32gb storage and that is more than enough for me (I am only using 3gb of space) so I wont need to add anymore storage.
I should also add that when multitasking without zram enabled, the tablet reboots less but still has done it, and so far nothing has been lost in my notebooks. I am thinking that the memory of 1gb is starting to reach its limit, with no apps running I am consuming about 600mbs of it.
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Click to collapse
Well in my own personal testing i could not see any benefit while extracting 700mb archives under android with 4gb swap space on a 40mbs microsd card, while under full linux desktop with a same workload, swap differently helps keep the system smooth under heavy io load. The conclusion i drew was the android platform deals to memory management differently than the typical desktop os, due to slower emmc chips used as a boot disk for the majority of android devices using this slow, already bottlenecked memory as swap space doesn't make sense (not to mention the use of 2gb swap space on a limited 16gb storage etc), so android runs almost completely in ram, with stricter memory management and allocation allows android to run fine without swap space, although because of this, androids memory management makes little uses of available swap space
JoinTheRealms said:
Well in my own personal testing i could not see any benefit while extracting 700mb archives under android with 4gb swap space on a 40mbs microsd card, while under full linux desktop with a same workload, swap differently helps keep the system smooth under heavy io load.
Click to expand...
Click to collapse
I've been running my desktop without swap for the last 10 years, and as long as you have enough RAM for all your running programs, there will be no problem at all.
Extracting an archive is a mostly sequential operation (single read stream, single write stream), so it also doesn't benefit from caching, which could use the memory that is freed by swapping.
_that said:
I've been running my desktop without swap for the last 10 years, and as long as you have enough RAM for all your running programs, there will be no problem at all.
Extracting an archive is a mostly sequential operation (single read stream, single write stream), so it also doesn't benefit from caching, which could use the memory that is freed by swapping.
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Click to collapse
Ahh that makes sense. I wasnt sure if swap had an effect directly on the extraction, but seem keeped the rest system more stable/ smooth duing the process in the case of GNU/Linux, with swap off similar operations such as installing packages would more oftern lock the tablet up. Might be a placebo though
I also dont set swap on my Linux desktop, as it has plenty of ram but the benitfit of swap space is somewhat more noticable due to the lack of ram on the tf700.
JoinTheRealms said:
I also dont set swap on my Linux desktop, as it has plenty of ram but the benitfit of swap space is somewhat more noticable due to the lack of ram on the tf700.
Click to expand...
Click to collapse
I just want to share my user experiences on the swap space... It does seem to improve the tf700 with swap space due to the lack of RAM (1GB)..
Thanks for all the useful posts
Thanks for all the posts, I have my sd card on the way. I will post my experience when I get my sd card but I am sure it is safe to say there will be a benefit. I use linux to at home and have 8 gigs of ram on that computer, I lessen the swap after install to about 512mb because 8 gigs is more then enough. I leave some however just incase of any issues like ram going bad. On another computer in the house that has limited ram (1.5 gigs) I have enabled zram (384 mb) and added two old flash cards (1 gig each) to a pci raid card and those were converted to swap. I then altered the fstab to reflect the order of priority I wanted them used in. The reason is that when the swap is used from the hard drive, and the hard drive is being written to, can cause a slow down. So with the 2 flash cards at 1 gig each (the swap seen as 2 gigs) it seemed to speed it up. I just posted that because of the nix users and it seemed like a good plan to run it that way.
Ok, got the sd card
So I recieved the sd card today and applied the swap space to it using root swapper (max setting is 256mb, I figured i can find a way to increase it later if I need to). The defaut location in many of the swap applications will not work on this device however, the sd card mounts at /storage/sdcard1 in my case. So it has to be entered manually (might just be cyanogenmod). Also the device was picky when insalling the card, it would only say blank sd card or cannot read filesystem. I had to install the card in the dock, format it from cwm recovery, (vfat if I remember correct, ext2 and ntfs had issues, avoided ext3 and ext4 cause journaling will cause more wear and tear).
The sd card is a scandisk ultra sdhc uhs-1 8 gigs. From my research that is the fastest this tab can handle. I also use optimising programs like greenify (epic save everything app), pimp my rom (almost every tweak applied), and some pretty efficient tweaks in the settings as well. I also have HALO))) installed and working (epic multiwindow app that works with native programs and almost any rom).
The resuts:
I tested it many ways, I rebooted to see use (none was used because swap starts after boot), I opened apps normally (browsers and things), and it showed 9kb's was used. I then put it to the tests, I open four windows in halo, these were youtube, moonreader pro with a pdf ebook, lecturenotes (awsome note and handwriting app with tons of functions), and Supernote pro (not the best note app). Constantly switched between the apps and messed with settings with them open. The max of swap used was around 10mb(keeping in mind that when I switch windows the app(s) I leave get paused making it hard to tell actual usage because I had to swith the terminal and type "free". I then ran antutu bechmark and gpubench (my tab stills score pretty well) and got a little higher swap usage but not much.
As for the feel of it, it seemed to help when opening many windows in halo, this is the primary reason for my doing this. As for other more normal uses I really didnt see too much of a difference, I did test games however and they did seem a little better (could be placebo) but I am not really sure why they would except android cached other apps to free memory. Reopening apps seemed faster. Also because of apps like greenify my memory usage is decreased so I am sure typically swap would have seen more use.
The conclusion is that at this point I really didn't notice much of a boost for any normal use, but I will definately keep the swap space on due to the boost when using halo and not to mention that I will be updating to android 4.4 soon and it might need more memory. Swap at this point seems more like a pre emptive strike, but it does help with multitasking.
about swap
://androidforums.com/boost-mobile-warp-all-things-root/610449-ram-swapping-without-swapper2.html I actually followed a guide on android central and redid the swap file to 1 gig to swap instead of using a program, this worked better. (add http in front), when i disabled swap it was noticeable that there was a boost. then reenabled it this method.