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top: improve/correct several memory fields in man page

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Due to quirks in kernel memory management plus limited
information available from /proc/<pid>/status & statm,
some of the top resident memory fields were capable of
exceeding available physical memory. So this commit is
a bit of a band-aid until the kernel has been changed.

Such a change appears to be on the horizon in the form
of three new fields to be added to /proc/<pid>/status.
While not preventing 'resident' memory from apparently
exceeding physical memory, the new fields will help to
clarify any such contingency, if/when we exploit them.

Reference(s):
. original post by Samuel Thibault
https://gitlab.com/procps-ng/procps/issues/21
. informative memory analysis
https://techtalk.intersec.com/2013/07/memory-part-1-memory-types/
https://techtalk.intersec.com/2013/07/memory-part-2-understanding-process-memory/
. kernel changes to /proc/<pid>/status
commit 8cee852ec53fb530f10ccabf1596734209ae336b
commit eca56ff906bdd0239485e8b47154a6e73dd9a2f3

Signed-off-by: Jim Warner <james.warner@comcast.net>
This commit is contained in:
Jim Warner 2016-03-14 00:00:00 -06:00 committed by Craig Small
parent e50ad77997
commit 6a36bd7afd
1 changed files with 18 additions and 8 deletions
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@ -42,7 +42,6 @@
.ds KA arrow key .ds KA arrow key
.ds KS scrolling key .ds KS scrolling key
.ds MP physical memory .ds MP physical memory
.ds MS shared memory
.ds MV virtual memory .ds MV virtual memory
.ds NT \fBNote\fR: .ds NT \fBNote\fR:
.ds PU CPU .ds PU CPU
@ -613,8 +612,10 @@ any truncated data.
.TP 4 .TP 4
7.\fB DATA \*(Em Data + Stack Size (KiB) \fR 7.\fB DATA \*(Em Data + Stack Size (KiB) \fR
The amount of \*(MP devoted to other than executable code, also known as The amount of private anonymous memory \fIreserved\fR by a process.
the Data Resident Set size or DRS. It is also known as the Data Resident Set or DRS.
Such memory may not yet be mapped to \*(MP (RES) but will always be
included in the \*(MV (VIRT) amount.
.TP 4 .TP 4
8.\fB ENVIRON \*(Em Environment variables \fR 8.\fB ENVIRON \*(Em Environment variables \fR
@ -704,7 +705,15 @@ And while the 2.6 kernel can be made mostly preemptible, it is not always so.
.TP 4 .TP 4
19.\fB RES \*(Em Resident Memory Size (KiB) \fR 19.\fB RES \*(Em Resident Memory Size (KiB) \fR
The non-swapped \*(MP a task is using. A subset of the virtual address space (VIRT) representing the non-swapped
\*(MP a task is currently using.
It can include private anonymous pages, private pages mapped to files
(including program images and shared libraries) plus shared anonymous pages.
All such memory is backed by the swap file represented separately under SWAP.
Lastly, this field may also include shared file-backed pages which, when
modified, act as a dedicated swap file and thus will never impact SWAP.
.TP 4 .TP 4
20.\fB RUID \*(Em Real User Id \fR 20.\fB RUID \*(Em Real User Id \fR
@ -731,10 +740,11 @@ depending on \*(We's delay interval and nice value.
.TP 4 .TP 4
23.\fB SHR \*(Em Shared Memory Size (KiB) \fR 23.\fB SHR \*(Em Shared Memory Size (KiB) \fR
The amount of \*(MS available to a task, not all of which is A subset of resident memory (RES) that may be used by other processes.
typically resident.
It simply reflects memory that could be potentially shared with It will include shared anonymous pages and shared file-backed pages.
other processes. It also includes \fIprivate\fR pages mapped to files representing
program images and shared libraries.
.TP 4 .TP 4
24.\fB SID \*(Em Session Id \fR 24.\fB SID \*(Em Session Id \fR