Why don't most Android devices have swap area as typical OS does?
Does any Android today support swap area which is suppose to boost the performance?
What are the considerations that make most Android devices drop that feature?
Answer
Does any Android today support swap area?
Quoting Dianne Hackborn:
To be a little more specific, it does use paging but not swap space. That is, it relies heavily on being able to mmap() files and have the kernel page in data from the file as needed (and drop those pages when not needed). It does not however use swap space for paging out dirty pages.
With some slightly adaptions, swap area can work with Android's default low memory killer together well, right?
I certainly would not assume that.
Does any Android today support swap area which is suppose to boost the performance?
It is not supposed to "boost the performance".
what's the considerations that make Android drop this idea?
First, on-board flash is slow, much slower than the hard drives and SSDs that you are used to on desktops and notebooks. And while the quality of the flash storage used on Android devices today is better than it used to be, it's still not screaming fast. That's why, for example, we have to take special care when doing database I/O, to use transactions, to limit the number if disk write operations.
Second, historically, on-board flash was limited in space. We didn't have enough internal storage for our apps, let alone to dedicate some for swap.
If you wish to discuss this further, please use a more appropriate forum, such as http://android.stackexchange.com, as your question is only tangentially related to software development.