Tenth Chapter Page Space

one, Virtual Memory Manager (VMM)

The memory in the AIX system is managed by VMM, which provides a 52-bit (bit) virtual address space (4 Petabytes) that is divided into segments of the same size (Segment) that become virtual memory segments (Virtual-memory Segment). The size of each segment is 256MB, the virtual memory segment is also divided into 4KB size units, the actual physical memory is also zoned 4KB-sized units, these units are called pages (page). The system is to exchange data between actual memory and virtual memory (secondary memory) in pages. RAM and disk memory pages are managed by VMM

two features of VMM:

1) Manage the allocation of the memory page structure, 2) schedule the virtual memory pages that need to be accessed that are not in the current RAM. To accomplish these functions, VMM maintains a space list of actual memory pages that are not currently in use (Fee list).

Reasons to use also page space:

1) When the actual memory is running out, use the specified page space as the second memory.

2) only the running program and the data being accessed are kept in real memory.

Page space allocation Policy (algorithm): Early and late algorithms. Defined by the PSALLOC environment variable, the system defaults to the late algorithm.

second, the size of the page space

Excessive page space does not improve the performance of the system, but it can reduce the efficiency of the use of memory, because too much page space will cause the system to frequent page exchange operations.

default page space size:

1) The page space cannot be less than 16MB (except Hd6). In the aix4.3+ version, HD6 cannot be less than 64MB.

2) page space cannot exceed 20% of the total disk space

3) If the actual memory is less than 256MB, the page space is twice times the actual memory

4) when the actual memory space is greater than or equal to 256MB, the page space is 512MB.

Total page space size:

1) The total size of all page space recommended in the general system should be at least twice times the amount of machine memory.

2) When the memory reaches 4GB~8GB, the page space is initially 3GB, then the usage of the page space is observed, and if more than 70% is used, the page space needs to be increased.

3) Ideally, you should make several page space sizes equal and spread across different physical volumes. If you want to create another page space, it is better to create a physical volume with a smaller load than the physical volume where ROOTVG is located, which can improve the performance of your page space.

4) When the system boots, only hd6 this basic page space is active, so the allocation of all the page space during the boot process occurs only on the basic page space. This means that the basic page space should be slightly larger than the second page space, and all the secondary page space should be the same size.

three, page space location

Page space is a logical volume that maximizes page space performance by determining the location of page space on disk.

1) Allocate the middle area of the disk to the page space to reduce the movement time of the head arm

2) Use multiple page spaces to allocate each page space to a separate physical volume, but it is also necessary to place a page space logical volume on each physical volume. If the operating system is installed on two or more disks, the required page space is split across all disks when the system is installed, and then named hd6n for each page space area

3) Move the most frequently used page space to infrequently accessed disks

4) Do not allocate multiple page space logical volumes on one physical volume

5) The size of each page space logical volume is basically equal

6) Do not extend a page space logical volume to multiple physical volumes

7) basic page space (HD6) should be modified under Maintenance mode (Maintenance mode)

four, close (deactive) page space

aix5l before the system shuts down a page space device

First, change the automatic activation (auto) property of this page space to no and restart the system

#chps-a n myps----> Modify Myps page space does not activate automatically at system startup

#shutdown-FR----> Restart system

#lsps-a----> Check the status of the page space

aix5l+ System closes a page space

#swapoff/dev/myps----> can also run Smitty Swapoff

If there is a limit on the size of the page space or I/O errors will cause the Swapoff command to fail because all pages to be closed (in the page space that will be closed) must be moved to another active page space

v. Manage the size of the page space

1) Increase the size of the page space

If you are prompted for content, you are running out of page space and need to increase the page space

#chps-S 5 paging00----> Add 5 logical partitions

Or

#extendlv paging00 5----> because page space is a logical volume of type paging, you can increase the page space by increasing the logical volume size

2) Reduce the size of a user-defined page space for a previous version of aix5l

#chps-a n myps----> set boot not on

#mkps-N-ROOTVG hdisk0----> Create a temporary page space

#shutdown-FR----> Restart

#rmps Myps or # RMLV myps----> Delete page space

#mklv-T paging-y myps ROOTVG----> re-structuring this page space with reduced capacity

#chps-A Y myps----> Set boot up

#chps-a n paging00----> Set temporary page space boot not on

#shutdown-FR----> Restart

#rmps paging00 or #rmlv paging00----> Remove Temporary page space

3) Reduce a page space size in aix5l (including system hd6 and user-defined page space)

#chps-D 6 paging00----> Decrease of 6 logical partitions

Special Note : If Chps is called/USR/SBIN/SHRINKPS script to reduce the page space, the SHRINKPS command creates a temporary page space, so the page space does not have enough empty pp to allocate in the volume group. If you reduce the size of the basic page space Hd6, SHRINKPS will prevent the user from reducing its size to less than 32MB or deleting it. At the same time Shrinkps will temporarily build a page space and have the boot image and/sbin/rc.boot temporarily point to this temporarily created basic page space

4) Before aix5l system China reduces the size of Hd6

#lspv-L HDISK0----> see which logical volumes and file systems are distributed on the physical volume Hdisk0

#mkps-a-n-s ROOTVG hdisk0----> temporarily creates a new file system on Hdisk0 and activates immediately (-N)

#chps-a n hd6----> Set HD6 boot does not start ( note the difference between "-a N" and "-a-n " in the parameters of Mkps)

Change the string "Swapon/dev/hd6" to "SWAPON/DEV/PAGING01" in the/sbin/rc.boot file

#sysdumpdev-L----> Check basic dump device name

#sysdumpdev-P-P/DEV/PAGING01----> renaming a basic dump device to another space device (such as a newly created PAGING01)

#bosboot-D/dev/hdisk0-a----> Update boot boot image on Hdisk0

#shutdown-FR----> Restart

#rmps hd6----> Delete hd6

#mklv-T paging-y hd6 ROOTVG----> Reconstruction hd6, according to reduced volume

#sysdumpdev-P-P/DEV/HD6----> change basic dump Device to HD6

#bosboot-D/dev/hdisk0-a----> Refresh boot boot image under Hdisk0

#chps-A Y hd6----> Setup hd6 boot up

#chps-a n paging01----> set PAGING01 boot not on

#shutdown-FR----> Restart

#rmps paging01----> Delete temporary paging file paging01

#migratepv-L HD6 hdisk0 hdisk1----> This command is used to migrate hd6, regardless of the above steps .

Tenth Chapter Page Space