How to calculate heap size of process from address space?

Question

I was trying to find the heap size my process is using. I did

fgrep '[stack]' /proc/pid/maps and got

00a00000-45937000 rw-p 00000000 00:00 0 [heap]

Now I wanted to calculate the size of the heap. So I did

(45937000 - 00a00000 ) = 44F37000

converted it to decimal 1156804608. Then to GB = 1156804608/(1000*1000*1000) = 1.1568 GB.

Is what I am doing correct?

Is this the right way to get the heap memory – Srikan Feb 07 '18 at 17:20 — Srikan, Feb 07 '18 at 17:20
Should [stack] be [heap] in that fgrep invocation? – Kusalananda Feb 11 '18 at 00:15 — Kusalananda, Feb 11 '18 at 00:15

score 1 · Answer 1 · answered Feb 11 '18 at 09:53

Yes, taking the end boundary address minus the start boundary address will give you the size of the heap in that particular process.

The calculation may be carried in the shell with

hsize=$(( 0x45937000 - 0x00a00000 + 1 ))
printf 'heap is %d bytes (about %d MiB)\n' \
    "$hsize" "$(( hsize / 1024 / 1024 ))"

With GNU awk parsing the maps "file" for PID $pid (GNU awk needs -n to be able to recognize non-decimal integers):

awk -n -F '[- ]' '/\[heap\]/ {
    h = "0x" $2 - "0x" $1 + 1
    printf("heap is %d bytes (%.2f MiB)\n", h, h/1024/1024) }' /proc/$pid/maps

This question on ServerFault may also be useful, depending on what you would want to do: Dump a linux process's memory to file

1 Answers1