Memory Management in RHEL Linux vs AIX

[Former Member]

Hi Experts,

We are installing new dialog servers on RHEL Linux for our ECC Prod System (ERP EHP6 SPS10 Kernel 721 Ext UC patch 333) with CI & DI currently running on AIX 6,1 with DB2 v 10.1 fp2.

until this time we were using the memory management for AIX with ES/TABLE parameter set to SHM_SEGS which is special implementation for AIX & we had the following parameters set:

EM/TOTAL_SIZE_MB

EM/TOTAL_SIZE_MB

ES/SHM_PROC_SEG_COUNT

ES/SHM_MAX_PRIV_SEGS

ES/SHM_USER_COUNT

ES/SHM_SEG_COUNT

ES/SHM_SEG_SIZE

We have checked the SAP note 941735 which says to remove the ES/TABLE = SHM_SEGS & use by default value which is UNIX_STD & remove EM/TOTAL_SIZE_MB. The note also recomends to use es/implelmentation = std for 64 bit requirement.

With using AIX Special Implementaion we had dialog & background processes behaving in the same manner which was using roll memory followed by em followed by roll memory & then heap memory.

With the Linux implementaion the notes says that allocation sequence will change which means before going to EM background work process will use the Heap Memory first followed by heap or EM.

We used to think if any work process is using the heap memory it will show the status of work process as in priv mode but we dont know what will happen with new implementaion on Linux.

Please help me If somebody has very good understanding of Linux. I will really appreciate your help.

Regards,

Ajay Sehgal

[divyanshu_srivastava3 · Accepted solution]

Hi Ajay,

es/implelmentation = std

1st of all, this parameter makes your task bit easy. This makes sure Linux follows the standard Linux memory management. Here all the user contexts in system are mapped to the addressing space which is only possible in 64 bit systems as these systems can have huge memory configured which can be addressed at system level because of combination using 64 digit binary number.

allocation sequence will change

2nd point is, yes it would. I would suggest you to read below help section for more.

Allocating Memory for User Contexts (UNIX) - SAP Memory Management (BC-CST-MM) - SAP Library

Regards,

[isaias_freitas]

Hello,

A background work process will not enter in "priv mode". This is a state for dialog work processes only.

And even if it did, a background job starts and runs continuously at the same work process. So, there would be no difference any way.

I also recommend using "es/implelmentation = std".

Otherwise, if you face any issues related to memory management, and you open an SAP incident, SAP will recommend that you set it before anything else.

Regards,

Isaías

[former_member243992]

Hi Isaias,

My question here , how an OS recognize an dw process is a Dialog or background work process?

How OS know its, asking from OS perspective?

[isaias_freitas]

Hello,

The OS does now "know" this. This is relevant at SAP level only.

The "priv mode" is also something that happens at SAP level. The OS does not know this as well.

Regards,

Isaías