RE: Question about displaying process memory allocation on Linux

[Mark Rivers <rivers@cars.uchicago.edu>]

Hi Andrew,

Thanks for the hint.  

I was able to get the memory released back to the OS simply by setting the environment variable MALLOC_TRIM_THRESHOLD_ to a small value (1024) before starting the IOC.

Previously the VSZ, DRS, and RSS did not decrease much at all when I called emptyFreeList().

After setting MALLOC_TRIM_THRESHOLD_ to 1024 and collecting a bunch of arrays that allocate 3GB on the free list I see this, the same as before.

corvette:dxpSITORO/iocBoot/iocFalconX1>ps -p 145432 -o trs,vsz,drs,rss
 TRS    VSZ   DRS   RSS
15838 8321936 8306097 3237400

However, now after I call emptyFreeList() I see this.
corvette:dxpSITORO/iocBoot/iocFalconX1>ps -p 145432 -o trs,vsz,drs,rss
 TRS    VSZ   DRS   RSS
15838 5173204 5157365 88668

Note that the memory allocation has indeed decreased by 3GB, so the memory has been given back to the OS.

Thanks,
Mark



-----Original Message-----
From: tech-talk-bounces@aps.anl.gov <tech-talk-bounces@aps.anl.gov> On Behalf Of Andrew Johnson
Sent: Tuesday, June 26, 2018 11:02 AM
To: tech-talk@aps.anl.gov
Subject: Re: Question about displaying process memory allocation on Linux

Hi Mark,

On 06/26/2018 08:51 AM, Mark Rivers wrote:
> This is what I see after I process the EmptyFreeList record.  Note 
> that VSZ has only decreased by about 0.2GB, not by 3GB which I would 
> have expected.  Can anyone explain?
> 
> corvette:dxpSITORO/iocBoot/iocFalconX1>ps -p 115038 -o trs,vsz,drs
> 
> TRS    VSZ   DRS
> 
> 15838 7974816 7958977

On linux (using glibc) the C runtime library won't return memory back to the OS by default, but you can ask it to do so. The first answer to this StackOverflow question gives some explanation and pointers:

https://stackoverflow.com/questions/2215259/will-malloc-implementations-return-free-ed-memory-back-to-the-system

HTH,

- Andrew

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