Re: Active Memory never reclaimed please help me understand

[Mulyadi Santosa <mulyadi.santosa@xxxxxxxxx>]

On Wed, Sep 23, 2015 at 4:47 AM, Prem Kumar <prem.it.kumar@xxxxxxxxx> wrote:

also wondering if there is a way I can list Active memory map showing me what is cached?

-regards.

On Tue, Sep 22, 2015 at 3:08 PM, Prem Kumar <prem.it.kumar@xxxxxxxxx> wrote:

Dear All,

I have done quite a bit of reading on Active memory reported in /proc/meminfo and in short says it is never reclaimed unless absolutely necessary, and it caches the recently used files/pages in memory. Although I fail to understand the consequences that I face here. 

I have disk-less and swap-less nodes. So all I have to do, is play with the RAM on the box. Issue that brought me here is investigating why after running some applications, used memory is never available for use with any other applications. 

In other words I cannot run any programs that requests memory more than what is shown as free in the output of free command and MemFree in the output of the cat /proc/meminfo

For example if I ran any program that requires more than 6GB on the first node below and more than 1GB on the second node below they fail instantly, and work fine if within the limist of free. There is nothing else running on the system other than system processes/services. 

             total       used       free     shared    buffers     cached

Mem:            23         17          6          0          0          9

-/+ buffers/cache:          8         15

Swap:            0          0          0

             total       used       free     shared    buffers     cached

Mem:            23         22          1          0          0          0

-/+ buffers/cache:         21          1

Swap:            0          0          0

Since the applications that ran previously are not running any more "even though they died out of memory because they requested more memory than available", shouldn't the OS see that any memory used previously as useless and can it not reclaim that for use with the next job/program on that machine. 

On every machine that I have run into this problem the out put of /proc/meminfo shows that Active memory is used up the amount shown in the free command and limits my further runs. 

This is driving me insane and making me feel stupid knowing that OS is smart enough to handle this, then what am I missing here to understand? Please advise. 

Appreciate any insight into this. 

Best Regards,

Prem

Dear Prem

welcome to kernelnewbies :) First of all, please don't do top posting when replying. Follow like what I and the rest of list member do.

Btw, looking from the free output, I have a doubt about your statement that your first application took 6 GB and secondly it took 1 GB. Assuming your application doesn't thing like memory locking in kernel space, i guess it takes 20+ GB of RAM.

So, before we go further, could you re run your applications and use ps or top to see both the VSIZE and RSS they take ?

Regarding memory claiming, yes after app is killed (using any ways possible: ctrl-c, sending kill/term/quit signal, OOM etc), any memory allocated by this task are freed. It happen on both active and inactive pages

--

regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com

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