Reducing default stack size from 8 MB to 8 KB - is it possible?

[medvednikov]

Hi,

I reduced the default stack size from 8 MB to 8 KB. Surprisingly RAM usage remained the same in our test program which launches thousands of coroutines. Also they take a lot more time.

Is there a certain minimum it can't be lower than?

Go uses 2-4 KB, I thought it'd be possible with photon as well.

Thanks.

[medvednikov]

This is the change I did:

-g.writeln('photon_thread_create((void*)${wrapper_fn_name}, &${arg_tmp_var});')
+g.writeln('photon_thread_create((void*)${wrapper_fn_name}, &${arg_tmp_var}, 8 * 1024);')

[beef9999]

All modern OS kernels will delay the real allocation of the physical memory pages until they are actually accessed. So the memory will not add 8MB immediately after every malloc.

Furthermore, we recently add mprotect to prevent out-of-bound memory access on small stack. https://github.com/alibaba/PhotonLibOS/pull/464/files#diff-f0db3c6fae5cc5fe519ada39d68af66b8c177096a3ee36c0d92893be964cf34c

[Coldwings]

The stack size is able to be set, parameters when creating threads. like photon::threada_create(entry, arg, STACK_SIZE), that feature has already provided.
Still, it can hardly be to smaller.

In 0.8 version, thread handle struct and mprotect page are located inside allocated stack space, those stuff asked at least two PAGE_SIZE as kernel provides (Yeah we have meet kernels provides 16KB pages in production environment). That means you might set at least three pages for stack.