- 我弄了一個script可以用來profile process的各種記憶體狀態，並且紀錄hprof file
[Github Link]
使用mat工具可以觀看hprof file. 需用hprof-conf轉檔。- google IO 示範memory analyzer的sample
- https://www.youtube.com/watch?v=_CruQY55HOk
中文blog翻譯
- 一些名詞解釋。
Shallow heap和Retained heap。Shallow heap表示對象本身所占內存大小，一個內存大小100bytes的對象Shallow heap就是100bytes。Retained heap表示通過回收這一個對象總共能回收的內存，比方說一個100bytes的對象還直接或者間接地持有了另外3個100bytes的對象引用，回收這個對象的時候如果另外3個對象沒有其他引用也能被回收掉的時候，Retained heap就是400bytes。
VSS - Virtual Set Size 虛擬耗用內存（包含共享庫占用的內存） - RSS - Resident Set Size 實際使用物理內存（包含共享庫占用的內存）
- PSS - Proportional Set Size 實際使用的物理內存（比例分配共享庫占用的內存）
- USS - Unique Set Size 進程獨自占用的物理內存（不包含共享庫占用的內存）
一般來說內存占用大小有如下規律：VSS >= RSS >= PSS >= USS
Overview
The aim of this post is to provide information that will assist in interpreting memory reports from various tools so the true memory usage for Linux processes and the system can be determined.
Android has a tool called procrank (/system/xbin/procrank), which lists out the memory usage of Linux processes in order from highest to lowest usage. The sizes reported per process are VSS, RSS, PSS, and USS.
For the sake of simplicity in this description, memory will be expressed in terms of pages, rather than bytes. Linux systems like ours manage memory in 4096 byte pages at the lowest level.
VSS (reported as VSZ from ps) is . This size also includes memory that may not be resident in RAM like mallocs that have been allocated but not written to. VSS is of very little use for determing real memory usage of a process.
RSS is the. RSS can be misleading, because it reports the total all of the shared libraries that the process uses, even though a shared library is only loaded into memory once regardless of how many processes use it. RSS is not an accurate representation of the memory usage for a single process.
PSS , i.e. if three processes all use a shared library that has 30 pages, that library will only contribute 10 pages to the PSS that is reported for each of the three processes. PSS is a very useful number because when the PSS for all processes in the system are summed together, that is a good representation for the total memory usage in the system. When a process is killed, the shared libraries that contributed to its PSS will be proportionally distributed to the PSS totals for the remaining processes still using that library. In this way PSS can be slightly misleading, because when a process is killed, PSS does not accurately represent the memory returned to the overall system.
USS is . USS is an extremely useful number because it indicates the true incremental cost of running a particular process. When a process is killed, the USS is the total memory that is actually returned to the system. USS is the best number to watch when initially suspicious of memory leaks in a process.
For systems that have Python available, there is also a nice tool called smem that will report memory statistics including all of these categories.
