Does iOS now use memory compression?

[Eug]

Well, does it? I'm trying to make sense of this screengrab:

 

[JAG87]

Well, mavericks and yosemite do, so why not iOS... perhaps A8X is now fast enough to do compression on the fly.

 

[postmortemIA]

lol used 17,179,869,183.47 GB of RAM?

per that graph there's 8GB of RAM, when all is added up, yet we all know that there's only 2GB on board.

 

[Eug]

Heh. I didn't even realize it said 17xxxx GB of RAM used when I posted that. It seems like this app is totally borked after the last update.

Here it is for my iPhone 5s. Doesn't make sense either.

I'm curious why they added the compressed category though since I was under the impression iOS didn't make use of memory compression (yet). Or maybe memory compression is happening only with certain hardware in iOS?

 

[sm625]

How I've always interpreted it is that the wired memory plus the compressed memory equals your total. But the problem is that this is memory before compression, so the only way you can tell the compression ratio is to take free space and add it to wired, and subtract that result from the total used. Then take that number and divide it into Compressed. In the case of the previous post, that would be (936.16 - (708.08 + 62.95)) / 362.17 = 45.6%

I dont know if that's right, but every time I tried it it always kind of made sense. I can see it being 45% compression ratio.

 

[Eug]

In the first pic I have 2.47 GB free so that doesn't make sense. The app is borked.

I'm just more concerned with whether or not iOS truly has compression. I had read that in iOS 7 the capability was there but it was not used, and I had been under the impression the same was true in iOS 8. I hadn't read otherwise either. It'd be nice to know either way.

 

[tipoo]

Well, mavericks and yosemite do, so why not iOS... perhaps A8X is now fast enough to do compression on the fly.

That begs the question, which SoCs do it? Will an A5 compress memory? Those need it most, with 512MB causing jank all over the place. On the other hand compression could kill its already weak CPU performance.

EDIT: Tried it on a family members iPad Mini, doesn't seem to make sense. 870MB L3 cache for one, lol. And then the app memory is only using >3MB even when I open a bunch of stuff and switch to bmssm quickly. File cache is the second largest at 76MB, wired is 96MB...Compressed is a paltry 400KB so it doesn't seem to be compressing much, but the ability is there. 30MB free...So this doesn't add up to anywhere close to the 502 available.

 

[Eug]

That begs the question, which SoCs do it? Will an A5 compress memory? Those need it most, with 512MB causing jank all over the place. On the other hand compression could kill its already weak CPU performance.

I came across this log from last year in iOS 7 for the 64-bit iPhone 5S (with Apple A7), which shows memory compression being active.

http://forums.macrumors.com/showpost.php?p=18271162&postcount=13

That doesn't tell me anything about the 32-bit iPhones running iOS 7 (A4-A6) or iOS 8 though.

 

[tipoo]

I came across this log from last year in iOS 7 for the 64-bit iPhone 5S (with Apple A7), which shows memory compression being active.

http://forums.macrumors.com/showpost.php?p=18271162&postcount=13

That doesn't tell me anything about the 32-bit iPhones running iOS 7 (A4-A6) or iOS 8 though.

I got the app on an A5 device (Mini) and it does have compression, but it wasn't compressing much at all. 400KB, which is nothing. No matter what I opened it didn't seem to compress much.

So I'm guessing the capability is there, but as the CPU is much weaker it's much less aggressive than newer SoCs at doing it, to reduce CPU load.