Android NDK: Dalvik Heap and Native Heap - How Separate Between the two

Question

I know there\'s Dalvik(JVM) heap and Native heap in an android platform. And the Dalvik GC has no work on native heap. But I\'m not sure how this work, I mean how the Android OS

Answer 1

It is almost your second case

There are 2 separate heaps, one for the runtime Art(previously DalvikVM), and one for the native programs.

You can easily see these two different areas by performing a cat on the maps pseudo-file of the proc filesystem.

Consider the following output:

2a028000-2a029000 rw-p 00000000 00:00 0          [heap]
b6400000-b6c00000 rw-p 00000000 00:00 0          [anon:libc_malloc]

In the above example, the first area, that is only 1 page long, it is managed by the ART Runtime. Both dlmalloc and rosalloc are supported, but ART uses rosalloc since it is faster. This area, in contrast to what @fadden said (at least for Lollipop), is managed by sbrk. It grows upwards.

The second area, that is 2048 pages long, it is the native heap. It is used by the bionic library, which is an implementation of libc for Android. Both dlmalloc and jemalloc are supported, and the one that it is being used depends on the device. I haven't found a call that extends this heap, but I guess mmap would suffice. It grows downwards, towards the runtime heap.