mjhjmtu

In the manpage of top,

• Why are "program images and shared libraries" in #3 "considered private to a process", if "they will be accounted for as shared (SHR) by the kernel"?




• In what "private" sense are "program images and shared libraries" "considered private to a process"? Are "program images and shared libraries" read only?




• In what "shared" sense are "program images and shared libraries" "accounted for as shared (SHR) by the kernel"?




• "the swap file only includes #1 through #3. The memory in quadrant #4, when modified, acts as its own dedicated swap file." Do "program images and shared libraries" act as their own dedicated swap files too?

Thanks.

For each such process, every memory page is restricted to a single
quadrant from the table below. Both physical memory and virtual

memory can include any of the four, while the swap file only includes #1 through #3. The memory in quadrant #4, when modified, acts as its own dedicated swap file.

 Private | Shared
 1 | 2
 Anonymous . stack |
 . malloc() |
 . brk()/sbrk() | . POSIX shm*
 . mmap(PRIVATE, ANON) | . mmap(SHARED, ANON)
 -----------------------+----------------------
 . mmap(PRIVATE, fd) | . mmap(SHARED, fd)
 File-backed . pgms/shared libs |
 3 | 4

The following may help in interpreting process level memory values
displayed as scalable columns and discussed under topic `3a.DESCRIPTIONS of Fields'.

 SHR - subset of RES (excludes 1, includes all 2 & 4, some 3)

Note: Even though program images and shared libraries are considered
private to a process, they will be accounted for as shared (SHR) by
the kernel.