Possible working method to get actual process size on Linux

[Florian Weimer]

* Stefan Reich:

> OK, here is the code:
> https://github.com/stefan-reich/LinuxProcessSizeDetector
>
> Can this be linked somewhere? I believe it to be useful. Seems to work on
> the machines I tested it on, even though there is mild guesswork involved.

With a recent-enough kernel, you will see this:

$ grep ^[^A-Z] /proc/21679/smaps | grep memfd | sort -k3
40000000000-40001000000 rw-s 00000000 00:05 253242                       /memfd:java_heap (deleted)
80000000000-80001000000 rw-s 00000000 00:05 253242                       /memfd:java_heap (deleted)
100000000000-100001000000 rw-s 00000000 00:05 253242                     /memfd:java_heap (deleted)
7fffe000000-80000000000 rw-s 01000000 00:05 253242                       /memfd:java_heap (deleted)
bfffe000000-c0000000000 rw-s 01000000 00:05 253242                       /memfd:java_heap (deleted)
13fffe000000-140000000000 rw-s 01000000 00:05 253242                     /memfd:java_heap (deleted)
40001000000-40002000000 rw-s 03000000 00:05 253242                       /memfd:java_heap (deleted)
80001000000-80002000000 rw-s 03000000 00:05 253242                       /memfd:java_heap (deleted)
100001000000-100002000000 rw-s 03000000 00:05 253242                     /memfd:java_heap (deleted)
7fffc000000-7fffe000000 rw-s 04000000 00:05 253242                       /memfd:java_heap (deleted)
bfffc000000-bfffe000000 rw-s 04000000 00:05 253242                       /memfd:java_heap (deleted)
13fffc000000-13fffe000000 rw-s 04000000 00:05 253242                     /memfd:java_heap (deleted)
40002000000-4000ec00000 rw-s 06000000 00:05 253242                       /memfd:java_heap (deleted)
80002000000-8000ec00000 rw-s 06000000 00:05 253242                       /memfd:java_heap (deleted)
100002000000-10000ec00000 rw-s 06000000 00:05 253242                     /memfd:java_heap (deleted)

That is, you can recover the information which mapping aliases which
other mapping by looking at device/inode combination (column 4 and 5)
and the mapping offset (column 3).

I believe there is a tool called smem which does exactly that.