2011-02-27
Virtual Memory , HEAP
- 長久以來一直不是很懂 top 指令中,VIRT 、RES 與 SHR 的意義。今天還是來了解一下 manpage
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
o: VIRT -- Virtual Image (kb) The total amount of virtual memory used by the task. It includes all code, data and shared libraries plus pages that have been swapped out. VIRT = SWAP + RES. q: RES -- Resident size (kb) The non-swapped physical memory a task has used. t: SHR -- Shared Mem size (kb) The amount of shared memory used by a task. It simply reflects memory that could be potentially shared with other processes. p: SWAP -- Swapped size (kb) The swapped out portion of a task's total virtual memory image.
- 所以 RES 是目前正在使用中的「實體記憶體(physical memory)」,SHR 是不同程序之間共享的記憶體大小,VIRT 則是「虛擬記憶體(virtual memory)」,包括 CODE, DATA, 共享函式庫與 SWAP。
- 從「Virtual Memory Usage from Java under Linux, too much memory used」這篇討論,學到一個指令:pmap,隸屬於 procps 套件中。用法是 pmap -x $PID (不同身份時,得透過 sudo 取得記憶體狀態)
procps: /usr/bin/pmap
~$ sudo pmap -x $PID
jazz@drbl:~$ sudo pmap 24972 24972: /usr/bin/php5-cgi 0000000000400000 5144K r-x-- /usr/bin/php5-cgi 0000000000b06000 356K rw--- /usr/bin/php5-cgi 0000000000b5f000 32K rw--- [ anon ] 00000000010da000 2212K rw--- [ anon ] 00007f418a02b000 40K r-x-- /lib/libnss_files-2.7.so 00007f418a035000 2048K ----- /lib/libnss_files-2.7.so 00007f418a235000 8K rw--- /lib/libnss_files-2.7.so 00007f418a237000 28K r-x-- /usr/lib/php5/20060613/pdo_mysql.so 00007f418a23e000 2044K ----- /usr/lib/php5/20060613/pdo_mysql.so 00007f418a43d000 4K rw--- /usr/lib/php5/20060613/pdo_mysql.so ... 略 ...
- 根據「Avoid linux out-of-memory application teardown」這篇討論,如果出現虛擬記憶體使用過多,核心開始執行 out-of-memory(OOM) killer 的話,可以使用以下方法關閉:
1. Disable the OOM Killer (Put vm.oom-kill = 0 in /etc/sysctl.conf) 2. Disable memory overcommit (Put vm.overcommit_memory = 2 in /etc/sysctl.conf) Note that this is a trinary value: 0 = "estimate if we have enough RAM", 1 = "Always say yes", 2 = "say no if we don't have the memory")
- 關於 /proc/sys/vm 底下的檔案 - 說明詳見 vm.txt
linux-doc: /usr/share/doc/linux-doc/sysctl/vm.txt.gz
- 可以透過 sysctl 設定 swap - How do I free virtual memory in Ubuntu?
$ cat /proc/sys/vm/swappiness 60 $ sudo sysctl vm.swappiness=0 vm.swappiness = 0
- 20.如何取得記憶體的統計資料(memory statistics)? 介紹如何寫 Java 記憶體
public class MemoryStats{ public static void main(String args[]){ long totalMem = Runtime.getRuntime().totalMemory(); long freeMem = Runtime.getRuntime().freeMemory(); System.out.println("Total memory"+ totalMem); System.out.println("Free memory" + freeMem); } }
Last modified 14 years ago
Last modified on Feb 27, 2011, 11:14:46 PM