Home PC Games Linux Windows Database Network Programming Server Mobile  
  Home \ Linux \ Learn to read the source code of vmstat     - OpenSUSE / Linux network configuration (Linux)

- C ++ runtime environment built on CentOS 6.6 and Oracle database connection (Database)

- Linux RHCS basic maintenance commands (Linux)

- DRBD Principle and Features Overview (Server)

- IPTABLES configuration steps under Linux (Linux)

- Five programming fallacy (Programming)

- B-tree - ideas and implementation of C language code (Programming)

- How to install and configure in Ubuntu 14.10 'Weather Information Indicator' (Linux)

- CentOS 6.5_x64 install Oracle 11g R2 (Database)

- Install Open vSwitch under CentOS 6.5 (Linux)

- Dalvik heap memory management and recycling (Linux)

- VirtualBox install Windows 8.1 has encountered an error 0x000000C4 solutions (Linux)

- Tip: Use Cryptsetup U disk encryption (Linux)

- Verify the character set on MyCAT (Database)

- Construction Spark source and application development environment (Server)

- Two alert log ORA Errors (Database)

- OpenSIPS offline messaging feature set (Server)

- Linux based exercises, interview questions (Linux)

- Ubuntu modify DNS restart loss problem (Linux)

- Create Your Own Docker base image in two ways (Linux)

  Learn to read the source code of vmstat
  Add Date : 2018-11-21      
  vmstat -a command to see the active memory and inactive memory, but what do they mean it?

$ Vmstat-a
procs ----------- memory ------------- swap ------- io ----- system -------- cpu -----
r b swpd free inact active si so bi bo in cs us sy id wa st
Their meaning in manpage only gave a simple explanation, did not explain in detail:

inact: the amount of inactive memory (-a option).
active: the amount of active memory (-a option).

Here we try to understand exactly what it means. Vmstat by reading the source code (vmstat.c and proc / sysinfo.c) that, vmstat command is taken directly from the / proc / meminfo data:

$ Grep-i act / proc / meminfo
Active: 1767928 kB
Inactive: 1373760 kB
The / proc / meminfo data is generated in the following core functions:

fs / proc / meminfo.c:
0023staticint meminfo_proc_show (struct seq_file * m, void * v)
0024 {
0032unsignedlong pages [NR_LRU_LISTS];
0051for (lru = LRU_BASE; lru 0052 pages [lru] = global_page_state (NR_LRU_BASE + lru);
0095 "Active:% 8lu kB \ n"
0096 "Inactive:% 8lu kB \ n"
0097 "Active (anon):% 8lu kB \ n"
0098 "Inactive (anon):% 8lu kB \ n"
0099 "Active (file):% 8lu kB \ n"
0100 "Inactive (file):% 8lu kB \ n"
0148 K (pages [LRU_ACTIVE_ANON] + pages [LRU_ACTIVE_FILE]),
0149 K (pages [LRU_INACTIVE_ANON] + pages [LRU_INACTIVE_FILE]),
0150 K (pages [LRU_ACTIVE_ANON]),
0151 K (pages [LRU_INACTIVE_ANON]),
0152 K (pages [LRU_ACTIVE_FILE]),
0153 K (pages [LRU_INACTIVE_FILE]),
This code means that all statistical LRU list, which is equal to ACTIVE_ANON Active Memory and ACTIVE_FILE sum, Inactive Memory and INACTIVE_FILE INACTIVE_ANON equal sum.

LRU list is the Linux kernel memory pages to retrieve data structure algorithms (Page Frame Reclaiming Algorithm) used, LRU is an acronym for the Least Recently Used. The core idea of ​​this algorithm is: Recycling page should be the least recently used.

To achieve this goal, the ideal situation is that each page has an age term for recording the last time the page is accessed, but x86 CPU hardware does not support this feature, x86 CPU can do when you visit the page settings a flag Access bit, time can not be recorded.

So Linux kernel uses a compromise approach: It uses the LRU list list to just visited pages on the column header, the closer the end of the column is the longer unvisited pages, so although it can not access the recording time , but the use of the page in the relative positions of the LRU list can easily find the oldest page.

Linux kernel designed two LRU list: active list and inactive list, just visited pages into the active list, not a long time visited pages into the inactive list, this page recovered from the inactive list becomes simple. Kswapd kernel thread periodically the active list in qualifying moved to inactive list in the page, the transfer is done by refill_inactive_zone () completed. This code means that all statistical LRU list, which is equal to ACTIVE_ANON Active Memory and ACTIVE_FILE sum, Inactive Memory and INACTIVE_FILE INACTIVE_ANON equal sum.


vmstat see active / inactive memory on the active list are inactive list and the memory size. If the inactive list is large, indicating that the page can be recovered if necessary a lot; and if the inactive list is small, indicating that the page can be recovered much.

Active / inactive memory for user processes in terms of memory occupied by the kernel memory occupied (including slab) is not among them.

As seen in the source code ACTIVE_ANON and ACTIVE_FILE, respectively anonymous pages and mapped pages. User process is divided into two pages of memory: memory file associated with (such as program files, data files corresponding to the memory pages) and has nothing to do with the file memory (such as process stack, the application memory using malloc), the former is called file pages or mapped pages, the latter known as anonymous pages. In the event of paging file pages (page-in or page-out) when a read or write from its corresponding file; anonymous pages when paging occurs, the exchange zone is read / write operations.
- 20 Unix / Linux command skills (Linux)
- CentOS install SVN server configuration and automatically synchronized to the Web directory (Server)
- How to install Linux Go Language (Linux)
- Hardware Firewall Basics (Linux)
- GitLab Guide installation under Ubuntu 14.04 (Server)
- Oracle GoldenGate encryption (Database)
- PULL operation mechanism parsing XML Comments (Programming)
- Oracle PLS-00231 error analysis (Database)
- Ubuntu is expected to allow you to install the latest Nvidia Linux drivers easier (Linux)
- Installation of Gitlab under Ubuntu (Linux)
- Virtual Judge structures under Ubuntu 14.04 (Server)
- Experience CoreCLR stack unwinding characteristics of initial implementation on Linux / Mac (Linux)
- MySQL uses Federate engine mapping table to achieve operation of the local remote operation table (Database)
- Upgrade to Linux Mint 16 petra Mint 17 Qiana (Linux)
- DataGuard add temporary data files bug (Database)
- Installation of network monitoring ntopng under CentOS 6.4 (Linux)
- Linux file system data file deletion problem space is not freed (Database)
- How to install Ubuntu California - the calendar application (Linux)
- The Linux firewall is configured to use proxy (Linux)
- Cryptography development environment to build under Ubuntu (Linux)
  CopyRight 2002-2022 newfreesoft.com, All Rights Reserved.