Guide to changing your pagepool

[FormerPalmOS]

Originally Posted by keaolyen

i can only think of 1 or 2 other possibilities...

1) static keeps data in page pool on reset where static doesn't; normally this would be called volatile memory though...
2) static is always in the same physical location while dynamic moves around...

If a dynamic page pool doesn't mean that it changes in size as needed then I would think option 1 would be the most likely definition. But, as I pointed out there's already a term for that...

The pagepool is stored in RAM - the whole reason it exists is that you can't run code out of NAND flash storage - you have to copy it to RAM then execute it. If there ain't no room, you have to flush something out to make room. You can always copy it back in later. The amount of flushing and the corresponding performance hit while waiting to re-load something you need is why a bigger pagepool gives you better performance. Of course with a gimped VZW phone, if you have too big of a pagepool you don't have enough room to store the volitale data for whatever application you are running and it crashes. So it's a trade-off.

The physical location of the pagepool in memory doesn't matter - though I have no idea if it does or doesn't move.

Whatever is in the pagepool is lost at power-off. But it doesn't matter - everything in the pagepool got there by being copied from the flash anyway. The pagepool has a one way door. Stuff can be copied from NAND to the PP, but it is never written back - just scrapped.

The volitale data in the program memory (total RAM size minus pagepool size) must be written back to the NAND flash before power-off if it is to be saved.

[scrosler]

Originally Posted by FormerPalmOS

The pagepool is stored in RAM - the whole reason it exists is that you can't run code out of NAND flash storage - you have to copy it to RAM then execute it. If there ain't no room, you have to flush something out to make room. You can always copy it back in later. The amount of flushing and the corresponding performance hit while waiting to re-load something you need is why a bigger pagepool gives you better performance. Of course with a gimped VZW phone, if you have too big of a pagepool you don't have enough room to store the volitale data for whatever application you are running and it crashes. So it's a trade-off.

The physical location of the pagepool in memory doesn't matter - though I have no idea if it does or doesn't move.

Whatever is in the pagepool is lost at power-off. But it doesn't matter - everything in the pagepool got there by being copied from the flash anyway. The pagepool has a one way door. Stuff can be copied from NAND to the PP, but it is never written back - just scrapped.

The volitale data in the program memory (total RAM size minus pagepool size) must be written back to the NAND flash before power-off if it is to be saved.

Wow! Great job explaining that!

[gguruusa]

Originally Posted by keaolyen

i can only think of 1 or 2 other possibilities...

1) static keeps data in page pool on reset where static doesn't; normally this would be called volatile memory though...
2) static is always in the same physical location while dynamic moves around...

If a dynamic page pool doesn't mean that it changes in size as needed then I would think option 1 would be the most likely definition. But, as I pointed out there's already a term for that...

Nah, we all agree that dynamic means something about allocating on demand. What isn't clear to me is that FormerPalmOS's statement about how it is configured is correct. For example, maybe Dynamic(12) means dynamic, max of 12 MB. Or maybe Dynamic(12) means dynamic, minimum of 12 MB. I haven't seen anything official that says exactly how dynamic works in current kernels. It just doesn't strike me as reasonable that Microsoft would have modified the pagepool configuraton stuff for no apparent gain in flexibility.

[FormerPalmOS]

Originally Posted by gguruusa

Nah, we all agree that dynamic means something about allocating on demand. What isn't clear to me is that FormerPalmOS's statement about how it is configured is correct. For example, maybe Dynamic(12) means dynamic, max of 12 MB. Or maybe Dynamic(12) means dynamic, minimum of 12 MB. I haven't seen anything official that says exactly how dynamic works in current kernels. It just doesn't strike me as reasonable that Microsoft would have modified the pagepool configuraton stuff for no apparent gain in flexibility.

Good points - looking at it that way the pagepool is always dynamic in that it doesn't take what it doesn't need. But you don't get back what it isn't using if you have a size set.

All I've looked at so-far is the code for the Verizon TP. Before modification it checks some value and based on that value writes either 0xC0000 or 0x60000 to an address that everyone seems to agree sets the pagepool size. On my phone it ends up getting set to 6 so by changing the 0x60000 in the code to 0xC0000 in the code, I get 0xC0000 no matter what.

What the phone does after that, I have no idea. It could very well be what you are saying - dynamic up to 12MB. But with this value at 12MB, even if only 4MB has been allocated, I don't get the other 8MB back for program memory. But it will never go past 12MB. My understanding is that with a size of 0MB, I get whatever it isn't using as program memory, but there is no limit to how much it may use.

Again - my observations and comments are limited to a study of one device. I assume you have looked at many more devices than I have.

[gguruusa]

Originally Posted by FormerPalmOS

Again - my observations and comments are limited to a study of one device. I assume you have looked at many more devices than I have.

All I can really tell you is that things changed between vogue and kaiser releases and vzw touch pro is an odd animal.

[keaolyen]

I don't think this is a hardware issue as much as an OS memory allocation issue, I.E. just because this is a new hardware platform I wouldn't think the way the OS handles pagepool would change.

I'll take a look through Technet to see if there's any articles there that address this...

[Isriam]

So what static number would I use to set 48mb on a rom already coded at 32mb? I can find the string in the OP in 2 places, and verified it says 20 16 but I want to set it to 48mb static.

[keaolyen]

Originally Posted by FormerPalmOS

The pagepool is stored in RAM - the whole reason it exists is that you can't run code out of NAND flash storage - you have to copy it to RAM then execute it. If there ain't no room, you have to flush something out to make room. You can always copy it back in later. The amount of flushing and the corresponding performance hit while waiting to re-load something you need is why a bigger pagepool gives you better performance. Of course with a gimped VZW phone, if you have too big of a pagepool you don't have enough room to store the volitale data for whatever application you are running and it crashes. So it's a trade-off.

The physical location of the pagepool in memory doesn't matter - though I have no idea if it does or doesn't move.

Whatever is in the pagepool is lost at power-off. But it doesn't matter - everything in the pagepool got there by being copied from the flash anyway. The pagepool has a one way door. Stuff can be copied from NAND to the PP, but it is never written back - just scrapped.

The volitale data in the program memory (total RAM size minus pagepool size) must be written back to the NAND flash before power-off if it is to be saved.

Exactly, but I think this discussion was about how static vs dynamic pagepool worked. Whether or not you could set the size of the dynamic pagepool as you do with static or if the OS simply allocated more to the dynamic as needed. I believe there were two camps of thinking as to how it worked and I was trying to rationalize how it would work assuming it worked the way gguruusa thought it did.

I suppose it could be that you can set the limit of your dynamic pagepool then the OS would use what it needed up to that point but I don't think that makes sense as it would quickly fill up to that limit. There's really no good reason that I can think of that it would work that way.

I agree with you that setting a static pagepool size would be like (in a PC) overriding the system defaults and fixing your pagefile size so that it's always the same size; never shrinking or growing. Assuming you still think this way, I think that a dynamic pagepool works more like your pagefile in a Windows OS; that it grows and shrinks as needed.

Before, when PPC's had less memory to work with I believe that you would have needed to set a static size. With today's devices that have much more memory to work with I'm thinking that setting dynamic might be the way to go...

BTW, haven't had a chance to check Tech Net yet. I'm too busy with product launches right now but I will dig into it as soon as I get the chance.

[keaolyen]

Originally Posted by Isriam

So what static number would I use to set 48mb on a rom already coded at 32mb? I can find the string in the OP in 2 places, and verified it says 20 16 but I want to set it to 48mb static.

You would use 0C 15 to get 48MB but there's some discussion as to whether this results in a static or dynamic pagepool.

I believe everyone agrees that 30 16 would give you a 48MB static pagepool.

*edit - not enough coffee yet, added a better explanation...

[Isriam]

so 0C 16 for static 48mb correct?