From ABCs Volume 2 Chapter 4
Maintain those executable program in memory.
Executable programs -- a) load modules(a PDS member) b) program
objects(a PDSE member) must be loaded into both virtual storage and
central storage before they can be executed.
LPA -- Link pack area is a common non-getmainable virtual storage area.
It is built at IPL time by the load of load modules contained in
SYS1.LPALIB and its concatenations.
Modules found in LPA do not need to be brought into virtual storage on
request because they are already in virtual storage. The benefit of
having lots of load module in LPA is that it decreases the use of the
private areas.
LPA pages can be stolen but never paged out because there are always valid copies in the LPA page data set(loaded at IPL time).
CSA one use is Dynamic LPA, after IPL, new load modules are added to LPA, these modules are added to CSA. Since LPA borders is not alterable.
Page fault
Virtual memory
LPA我的理解是，LPA是针对虚拟存储的概念，将一些common modules的可执行文件对应到指定的虚拟地址，这样当外部程序调用时，就可以通过Link的方式，链接到这些common modules。所以称之为Link Pack Area。而module是在phycial memory还是disk中，则是与LPA无关的。
FLPA是一种不能承受page fault的module所在的位置，F表示fix page，不可以进行page fault，参见上述Page fault的链接，应该是minor page fault，FLPA中应该存在一张map指明这是一个minor page fault，不进行真实的page fault。That means these load modules must be kept in fix storage frame in central storage for the duration of IPL.
MLPA and FLPA exist only for the duration of IPL time.
Relationship of Datasets
PLPA
SYS1.PARMLIB.LPALST** 主要用于补充SYS1.LPALIB，使得我们可以添加自己想要的users program。
当系统进行cancatenation时，只检查MCAT，不会对UCAT进行检查，所以在编辑LPALST**时，如果数据集没有被catalog，需要指定VOLSER。
FLPA
SYS1.PARMLIB.IEAFIX**
INCLUDE LIBRARY(SYS1.LPALIB)
MODULE(**,**,**)
同样，也需要MCAT
MLPA
SYS1.PARMLIB.IEALPA**
MLPA 中INCLUDE的LIBRARY必须是PDS不能是PDSE，另一点需要注意的是MLPA默认LIBRARY都是AFP-authorized的。
LPA modules that have been replaced through IEALPA** are not physically removed from the PLPA or from the LPA directory. They are, however, logically replaced because, when one of them is requested, MLPA is searched first and the system does not examine the LPA directory that contains the name of the replaced module.
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Dynamic LPA
In SYS1.PARMLIB.PROG**
LPA ADD, LPA DELETE, LPA CSAMIN
COMMAND
SETPROG LPA,ADD/DELETE...
DISPLAY PROG,LPA...
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