Hi Oracle professionals,
Please advice us and give right direction.

We have database on 12c on OS Red Hat Enterprise Linux Server release 6.10 with memory settings:
SGA: 4928M
PGA: 1250M

OS memory: 8GB
CPU q-ty: 2
Huge Pages disabled.

It worked OK, with above settings before enabling Data Guard.

2) DG was enabled - then we got of messages like:

2018-08-28T09:02:50.604204+05:00
WARNING: Heavy swapping observed on system in last 5 mins.
Heavy swapping can lead to timeouts, poor performance, and instance eviction.
2018-08-28T09:02:52.420519+05:00
Errors in file /u01/app/oracle/diag/rdbms/pp_sm/PP_SM/trace/PP_SM_dbrm_32047.trc (incident=89163):
ORA-00700: soft internal error, arguments: [kskvmstatact: excessive swapping observed], [], [], [], [], [], [], [], [], [], [], []
Incident details in: /u01/app/oracle/diag/rdbms/pp_sm/PP_SM/incident/incdir_89163/PP_SM_dbrm_32047_i89163.trc
2018-08-28T09:03:47.866712+05:00
Dumping diagnostic data in directory=[cdmp_20180828090347], requested by (instance=1, osid=32047 (DBRM)), summary=[incident=89163].


Details in incident:
----- Beginning of Customized Incident Dump(s) -----
==========================================
INSTANCE-WIDE SWAP ALERT SUMMARY
------------------------------------------
WARNING: Heavy swapping observed on the system.
Heavy swapping can lead to timeouts, poor performance, and instance eviction.
To reduce swapping, reduce the memory usage of this database instance and/or
other applications running on this server.

total physical memory: 8001 MB
bytes swapped in/out in last 5 mins: 1003028 KB
cpu utilization: 98%

SGA_TARGET: 4928 MB

PGA_AGGREGATE_LIMIT: 0 MB
maximum PGA allocated since startup: 5554 MB
total PGA currently allocated: 4797 MB
PGA_AGGREGATE_TARGET: 1250 MB

Beware that PGA usage (5554 MB) exceeds PGA_AGGREGATE_TARGET (1250 MB).
Decrease PGA usage by lowering PGA_AGGREGATE_TARGET and PGA_AGGREGATE_LIMIT.

Reduce the memory usage of this database instance by lowering SGA_TARGET,
PGA_AGGREGATE_TARGET, and/or PGA_AGGREGATE_LIMIT.


*****************************************************************
----We added extra capacity as:
OS: extra 4 GB memory added (Total = 12 GB)
CPU a-TY: extra 2 CPU added (Total = 4 CPU)

also in DB level:
SGA: 8GB (was extended)
PGA: 1700M (was extended)
Huge Pages still disabled.

Then after DB was restarted.
1 day after, we continued getting above errors.

[TOC00000]
Jump to table of contents
Dump continued from file: /u01/app/oracle/diag/rdbms/pp_sm/PP_SM/trace/PP_SM_dbrm_3857.trc
[TOC00001]
ORA-00700: soft internal error, arguments: [kskvmstatact: excessive swapping observed], [], [], [], [], [], [], [], [], [], [], []

[TOC00001-END]
[TOC00002]
========= Dump for incident 94092 (ORA 700 [kskvmstatact: excessive swapping observed]) ========
[TOC00003]
----- Beginning of Customized Incident Dump(s) -----
==========================================
INSTANCE-WIDE SWAP ALERT SUMMARY
------------------------------------------
WARNING: Heavy swapping observed on the system.
Heavy swapping can lead to timeouts, poor performance, and instance eviction.
To reduce swapping, reduce the memory usage of this database instance and/or
other applications running on this server.

total physical memory: 12041 MB
bytes swapped in/out in last 5 mins: 771796 KB
cpu utilization: 91%

SGA_TARGET: 8192 MB

PGA_AGGREGATE_LIMIT: 0 MB
maximum PGA allocated since startup: 4446 MB
total PGA currently allocated: 4086 MB
PGA_AGGREGATE_TARGET: 1700 MB

Beware that PGA usage (4446 MB) exceeds PGA_AGGREGATE_TARGET (1700 MB).
Decrease PGA usage by lowering PGA_AGGREGATE_TARGET and PGA_AGGREGATE_LIMIT.

Reduce the memory usage of this database instance by lowering SGA_TARGET,
PGA_AGGREGATE_TARGET, and/or PGA_AGGREGATE_LIMIT.

*****************************************************************

So, I have questions - critical for us:
What could be the source of Heavy Swapping problem?
1. Enabling Data Guard? Its processes eat all memory? Before enabling DG, database worked OK without Huge Page enabling.
2. Disabled Huge Pages - caused low performance?
3. I have read somewhere that if OS Total Memory => 8GB - huge pages must be enabled.
Is it true? If there are any ORA DOCS saying that huge page enabling is MUST HAVE for data guard feature?

Also we tried to return back the state - Database without DG.
Even after disabling all enabled DG parameters (LOG_ARCHIVE_CONFIG, LOG_ARCHIVE_DEST_2,
LOG_ARCHIVE_DEST_STATE_2, FAL_CLIENT, FAL_SERVER, STANDBY_FILE_MANAGEMENT) & restarting DB
- we were getting the above errors - heavy swapping and low performance. We do not use DG broker.
I came to conclusion that after disabling DG parameters - Data Guard is not disabled,
because we continued getting the errors.
4.Is it possible to disable Data Guard (in states if DG Broker is not used), for it became standalone server, cutting from Standby DB server fully?

With regards!

select
  st.sid,
  s.name, 
  st.value
from v$statname s, v$sesstat st
where st.statistic# = s.statistic#
and s.name = 'session pga memory max';