How to get amount of allocated memory from within a process (heap size)

What would be a good way to determine the current heap size (VSZ) for a
process on Linux?

I always used sbrk(0) for that, which used to return the top of the
heap. However recently, to my dismay, I discovered that it does not work
on Linux – I successfully malloc()-ed 1GB, could confirm it with “ps -o
pid,vsz,args”, and yet sbrk(0) always returns the same value as right in
the beginning.

As a work around, I have to open /proc//stat and read out the 23d
field from there. However it is heavy and ugly, and I have a feeling
that such a thing should be done in a more elegant way.

Please help. Any suggestions will be greatly appreciated. I even tried
to play with mallinfo(), however could not figure out how to interpret
results.

Thank you,
Gennady B…

I always used sbrk(0) for that, which used to return the top of the
to play with mallinfo(), however could not figure out how to interpret
results.

gem install sys-proctable

Regards,

Dan

On Jul 24, 2009, at 5:50, “Daniel B.” [email protected] wrote:

What would be a good way to determine the current heap size (VSZ)

gem install sys-proctable

Regards,

Dan

Daniel, thanks for your suggestion. I looked how you do it on Linux,
and see that it is exactly how I described in my workaround - via /
proc/fd/stat. This works, however I am looking for some lighter
solution available from a process itself. Like sbrk(0), which
unfortunatelly is useless on Linux :frowning:

Thanks anyways, I will keep looking.

Gennady.

On Fri, Jul 24, 2009 at 5:28 PM, Gennady
Bystritsky[email protected] wrote:

What would be a good way to determine the current heap size (VSZ) for a process on Linux?

I always used sbrk(0) for that, which used to return the top of the heap. However recently, to my dismay, I discovered that it does not work on Linux – I successfully malloc()-ed 1GB, could confirm it with “ps -o pid,vsz,args”, and yet sbrk(0) always returns the same value as right in the beginning.

It this topic related to ruby?

Well, type “man malloc” and look for MMAP_THRESHOLD.
Increasing MMAP_THRESHOLD large enough forces malloc() to use brk()
instead of mmap(). sbrk(0) doesn’t care mmap()-ed memory.

What would be a good way to determine the current heap size (VSZ) for
Well, type “man malloc” and look for MMAP_THRESHOLD.
Increasing MMAP_THRESHOLD large enough forces malloc() to use brk()
instead of mmap(). sbrk(0) doesn’t care mmap()-ed memory.

Well, it is not directly related to Ruby, I admit ;-). However, knowing
how many bright people hang out on this list with at least one thing in
common – love for Ruby – I decided to give it a try. And was rewarded
for this with posts from Daniel and yourself. Thank you very much. I
figured already that mmap() is “to blame” for sbkr(0) “failures” on
Linux, however did not know about MMAP_THRESHOLD.

I just wanted to get the current memory consumption by the current
process, something externally available from “ps” as “vsz”. I ended up
adopting as a final solution my original work-around of opening
/proc//stat and reading out 23 field from there. Same approach is
used in Daniel B.'s great sys-proctable gem.

Once again, thank you guys very much. Ruby-talk to the rescue as usual
:slight_smile:

Sincerely,
Gennady B…

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