Canvas：
Specific to Nokia's S60 devices, and possibily applicable to other Symbian devices as well: do not create multiple instances of Canvas, as it is a high-overhead object whose native implementation creates RWindow and RBackupWindow instances, which are heavyweight objects, in heap memory. Each new Canvas creates a new "RWindow" and this is know to exhaust memory pretty quickly.

I agree with previous poster that writing in big chunks is better than both saving everything at once or writing multiple small chunks. Perhaps you could also use a new Thread for I/O operations and save-as-you-go pattern. That would avoid the memory spike as well.

Images are problematic in some devices, I would only use PNG instead of JPEG, as they have smaller heap overhead.

I have a presentation about optimization for S60 devices, not exclusively for games, but it can be of some help. Contact me if you need it.

我现在的做法是即用即建，在n81和a1200上没未出现问题。 这个问题待核实。

至于PNG比jpeg有更小的堆负担的情况，不祥。