[Interest] Question to members of the Qt team: why does an empty project consumes so much memory on iOS?

Nuno Santos nunosantos at imaginando.pt
Tue Apr 21 19:43:31 CEST 2015


Thiago,

Thanks for your explanation. 

Right now I don’t have a clue on how should I correctly measure occupied by one Qt app on iOS environment.

I need to dig it out.

Thanks,

Regards,

Nuno

> On 21 Apr 2015, at 18:30, Thiago Macieira <thiago.macieira at intel.com> wrote:
> 
> On Tuesday 21 April 2015 18:16:57 Nuno Santos wrote:
>> Thiago,
>> 
>> Sorry for not having replied to you. I missed your email.
>> 
>> "Is that 16 MB of heap? Or are you including sharable & discardable code
>> pages?”
>> 
>> Sorry but I really don’t know what to answer here.
>> 
>> I’m just launching a new and empty Qt Quick project on Xcode and looking to
>> the memory usage.
> 
> The point is that you're not measuring memory properly.
> 
> Let me take the example of Qt Creator
> 
> F   UID    PID   PPID PRI  NI    VSZ   RSS WCHAN  STAT TTY        TIME COMMAND
> 0  1000  51459   2285  20   0 3085928 127168 -    Sl+  pts/0      9:12 
> bin/qtcreator
> 
> How much memory is it consuming? Would you answer 2.94 GB? Maybe 124 MB?
> 
> The answer is yes and no for both numbers. It depends on what you're 
> measuring. And there are more numbers:
> 
> $ ~/src/owntools/rssanalyse/rssanalyse.pl `pidof qtcreator`
> Total mapped memory:     3085932 kB
>    of which is padding: 1933552 kB
>   of which swapped out: 669832 kB
>  of which likely stack: 32908 kB mapped, 108 kB resident (64 kB main, 44 kB 
> aux threads)
>  of which are resident: 130152 kB, 123534 kB proportionally shared
>        total anonymous: 98168 kB (75.4%)
>                 Shared: 10200 kB total (7.8% of RSS)
>              Breakdown: 3476 kB clean (34.1%), 6724 kB dirty (65.9%)
>                         3100 kB code (30.4%), 376 kB RO data (3.7%), 6724 kB 
> RW data (65.9%)
>                         0 kB heap (0.0%), 0 kB stack (0.0%), 0 kB other 
> (0.0%)
>                Private: 119952 kB total (92.2% of RSS)
>              Breakdown: 32600 kB clean (27.2%), 87352 kB dirty (72.8%)
>                         21768 kB code (18.1%), 1052 kB RO data (0.9%), 360 kB 
> RW data (0.3%)
>                         96652 kB heap (80.6%), 108 kB stack (0.1%), 12 kB 
> other (0.0%)
> 
> The number in VSZ is usually not quoted because, as you can see, 62% of it is 
> *padding* between sections of RAM.
> 
> 124 MB is how much it really uses in RAM, but 10 of those is clean & shared 
> and another 32 MB is clean & sharable (but not shared, because no other 
> process loads the Qt Creator libraries). All clean pages can be discarded on 
> memory pressure and reloaded from disk.
> 
> Then there's 654 MB that is swapped out.
> -- 
> Thiago Macieira - thiago.macieira (AT) intel.com
>  Software Architect - Intel Open Source Technology Center
> 
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