Re: Does file-mapping a memory allocation work around RAM limits?
Re: Does file-mapping a memory allocation work around RAM limits?
- Subject: Re: Does file-mapping a memory allocation work around RAM limits?
- From: Rick Mann <email@hidden>
- Date: Wed, 3 May 2017 23:51:58 -0700
> On May 3, 2017, at 23:27 , Doug Hill <email@hidden> wrote:
>
>
>> On May 3, 2017, at 6:21 PM, Rick Mann <email@hidden> wrote:
>>
>> Our iOS app works with very large data buffers (hundreds of MB). As you can imagine, we run into issues at times.
>>
>> I saw some sample code that used this technique, and it got me wondering if this actually works around the 600 MB limitation of some iOS devices (which begs another question: doss the large iPad Pro with 3GB of RAM also limit apps to 600 MB?).
>>
>> --
>> Rick Mann
>> email@hidden
>
> The limits of mmap should be the limits of the file system. Well, technically it’s limited by the size_t parameter which I guess is OS specific. But these days it should be what the VFS can handle.
>
> I just tried out this code snippet:
>
> http://www.linuxquestions.org/questions/programming-9/mmap-tutorial-c-c-511265/ <http://www.linuxquestions.org/questions/programming-9/mmap-tutorial-c-c-511265/>
>
> and set the size of the mapped file to 32GB Works fine on a Mac with 16GB of RAM.
>
> It is SLOOOOOOWWWWWW however. You have to move all that data across a bus after all. If you need to load 3GB of data from your file, I recommend making it happen on a background thread. And make some lights blink and play a happy tune while the user waits.
>
> Not sure what the limitation on some iOS devices you’re referring to. Is it dependent on the installed RAM? Are there other artificial limits?
Yeah, at least on 1 GB iOS devices, apps are limited to 600 MB (even if there's more available). I think there are subtleties to that (e.g. maybe texture memory isn't counted), I'm not sure.
--
Rick Mann
email@hidden
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