$ getent user_attr prime ...::::defaultpriv=basic,proc_lock_memory;...
$ swap -lh; swap -sh
swapfile dev swaplo blocks free
/dev/swap - 4K 4.0G 3.9G
total: 496M allocated + 170M reserved = 668M used, 18G available
$ ipcs -mA
IPC status ...
T ... KEY ... NATTCH SEGSZ CPID ... ISMATTCH PROJECT
Shared Memory:
$ zonestat 1 1
Collecting data for first interval...
Interval: 1, Duration: 0:00:01
SUMMARY Cpus/Online: 24/24 PhysMem: 23.9G VirtMem: 27.9G
---CPU---- --PhysMem-- --VirtMem-- --PhysNet--
ZONE USED %PART USED %USED USED %USED PBYTE %PUSE
[total] 0.26 1.09% 7719M 31.4% 10.0G 35.8% 540K 0.00%
[system] 0.26 1.09% 7632M 31.0% 9.9G 35.4% - -
... 0.00 0.00% 86.9M 0.35% 117M 0.40% 1280 0.00%
Getting shared memory.
Press <ENTER>
Success!
$ swap -lh; swap -sh
swapfile dev swaplo blocks free
/dev/swap - 4K 4.0G 3.9G
total: 496M allocated + 1.2G reserved = 1.7G used, 17G available
$ ipcs -mA
IPC status ...
T ... KEY ... NATTCH SEGSZ CPID ... ISMATTCH PROJECT
Shared Memory:
m ... 0x1 ... 0 1073741824 3253 ... 0 group.staff
$ zonestat 1 1
Collecting data for first interval...
Interval: 1, Duration: 0:00:01
SUMMARY Cpus/Online: 24/24 PhysMem: 23.9G VirtMem: 27.9G
---CPU---- --PhysMem-- --VirtMem-- --PhysNet--
ZONE USED %PART USED %USED USED %USED PBYTE %PUSE
[total] 0.25 1.05% 7720M 31.4% 11.0G 39.4% 317 0.00%
[system] 0.25 1.05% 7633M 31.0% 9.9G 35.4% - -
... 0.00 0.00% 86.9M 0.35% 1144M 3.99% 317 0.00%
$ prstat -c -p 3253 1 1
Please wait...
PID USERNAME SIZE RSS ...
3253 ... 3832K 1720K
...
Attaching to shared memory.
Press
Success!
$ swap -lh; swap -sh
swapfile dev swaplo blocks free
/dev/swap - 4K 4.0G 3.9G
total: 1.5G allocated + 182M reserved = 1.7G used, 17G available
$ ipcs -mA
IPC status ...
T ... KEY ... NATTCH SEGSZ CPID ... ISMATTCH PROJECT
Shared Memory:
m ... 0x1 ... 1 1073741824 3253 ... 1 group.staff
$ zonestat 1 1
Collecting data for first interval...
Interval: 1, Duration: 0:00:01
SUMMARY Cpus/Online: 24/24 PhysMem: 23.9G VirtMem: 27.9G
---CPU---- --PhysMem-- --VirtMem-- --PhysNet--
ZONE USED %PART USED %USED USED %USED PBYTE %PUSE
[total] 0.25 1.07% 8741M 35.5% 11.0G 39.4% 1347 0.00%
[system] 0.25 1.06% 7631M 31.0% 9.9G 35.4% - -
... 0.00 0.00% 1109M 4.51% 1148M 4.00% 1347 0.00%
$ prstat -c -p 3253 1 1
Please wait...
PID USERNAME SIZE RSS ...
3253 ... 1028M 1026M ...
...
$ pmap -x 3253 | head
3253: ./shm_v04
Address Kbytes RSS ... Locked Mode Mapped File
08050000 8 8 ... - r-x-- shm_v04
08061000 4 4 ... - rwx-- shm_v04
08062000 128 44 ... - rwx-- [ heap ]
80000000 1048576 1048576 ... 1048576 rwxsR [ ism shmid=... ]
...
Locking shared memory.
Press
Success!
not relevant for ISM
Using shared memory.
Press
Success!
not relevant for ISM
Unlocking shared memory.
Press <ENTER>
Success!
not relevant for ISM
Detaching shared memory.
Press <ENTER>
Success!
$ swap -lh; swap -sh
swapfile dev swaplo blocks free
/dev/swap - 4K 4.0G 3.9G
total: 1.5G allocated + 182M reserved = 1.7G used, 17G available
$ ipcs -mA
IPC status ...
T ... KEY ... NATTCH SEGSZ CPID ... ISMATTCH PROJECT
Shared Memory:
m ... 0x1 ... 0 1073741824 3253 ... 0 group.staff
$ zonestat 1 1
Collecting data for first interval...
Interval: 1, Duration: 0:00:01
SUMMARY Cpus/Online: 24/24 PhysMem: 23.9G VirtMem: 27.9G
---CPU---- --PhysMem-- --VirtMem-- --PhysNet--
ZONE USED %PART USED %USED USED %USED PBYTE %PUSE
[total] 0.24 1.03% 8742M 35.5% 11.0G 39.4% 228 0.00%
[system] 0.24 1.03% 8656M 35.2% 9.9G 35.4% - -
... 0.00 0.00% 85.9M 0.34% 1143M 3.99% 228 0.00%
$ prstat -c -p 3253 1 1
Please wait...
PID USERNAME SIZE RSS ...
3253 ... 3832K 1720K ...
...
$ pmap -x 3253 | head
3253: ./shm_v04
Address Kbytes RSS ... Locked Mode Mapped File
08050000 8 8 ... - r-x-- shm_v04
08061000 4 4 ... - rwx-- shm_v04
08062000 128 44 ... - rwx-- [ heap ]
FE380000 24 12 ... - rwx-- [ anon ]
...
Removing shared memory.
Press
Success!
$ swap -lh; swap -sh
swapfile dev swaplo blocks free
/dev/swap - 4K 4.0G 3.9G
total: 496M allocated + 174M reserved = 668M used, 18G available
$ ipcs -mA
IPC status ...
T ... KEY ... NATTCH SEGSZ CPID ... ISMATTCH PROJECT
Shared Memory:
$ zonestat 1 1
Collecting data for first interval...
Interval: 1, Duration: 0:00:01
SUMMARY Cpus/Online: 24/24 PhysMem: 23.9G VirtMem: 27.9G
---CPU---- --PhysMem-- --VirtMem-- --PhysNet--
ZONE USED %PART USED %USED USED %USED PBYTE %PUSE
[total] 0.30 1.25% 7718M 31.4% 10.0G 35.8% 9852 0.00%
[system] 0.30 1.25% 7632M 31.0% 9.9G 35.4% - -
... 0.00 0.00% 85.9M 0.34% 120M 0.41% 228 0.00%
$ prstat -c -p 3253 1 1
Please wait...
PID USERNAME SIZE RSS ...
3253 ... 3832K 1720K ...
...
Exiting program.
Press
When Oracle Database fellows argues that "::shmget() requires swap reservation" they induce sysadmins to confusion or error.
As seen above (on the 2nd "output group") what happens is simply virtual memory reservation within the kernel. Note there's no other swap maneuver or switch between disk and physical memory and so on. The process that does the call doesn't even exhibit different figures.
With ISM, physical memory actually gets allocated only when the reserved shared segment is mapped in the calling process via ::shmat(). This is clearly seen in the 3rd "output group" above.
We also see that ::shmdt() doesn't really release any allocated memory as seen in the 4th "output group". The shared memory segment is unmapped from the process but continues to exist within the kernel.
It's only when ::shmctl() is called that memory is actually freed (fifth "output group").
