Changes between Initial Version and Version 1 of jazz/11-02-27

Timestamp:

Feb 27, 2011, 10:16:40 PM (13 years ago)

Author:

jazz

Comment:

--

jazz/11-02-27

@@ +1 @@
+= 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「[http://stackoverflow.com/questions/561245/virtual-memory-usage-from-java-under-linux-too-much-memory-used 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 [http://packages.debian.org/procps 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「[http://serverfault.com/questions/141988/avoid-linux-out-of-memory-application-teardown 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 - [http://superuser.com/questions/115565/how-do-i-free-virtual-memory-in-ubuntu How do I free virtual memory in Ubuntu?]
+{{{
+$ cat /proc/sys/vm/swappiness
+60
+$ sudo sysctl vm.swappiness=0
+vm.swappiness = 0
+}}}