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Operating Systems Solaris Monitoring Paging and Swapping Post 303027366 by jlliagre on Friday 14th of December 2018 09:28:04 AM
Old 12-14-2018
Quote:
Originally Posted by javanoob
Hi Jilliagre
There's an extra "i", my pseudo is jlliagre, not jilliagre...
Quote:
q1) Do you mean if ProcessA has made reservation on the virtual swap (ram & disk), another Process B can actually use this reserved space for actual physical paging into RAM and out to swap/disk ?
Unless shared memory enter in the game, no it can't.
Virtual space allocated by a process is for its exclusive use. Note again that virtual memory is not the same as physical memory. No particular space is reserved, that's just an amount of space. The OS is free to map this virtual space to whatever physical backend it likes.
Quote:
q2) If i still have free memory (ard 10G reported in memstat's free) but have physical swap being used (ard 3G in swap -l), what does this means then ?
That means the OS stored 3G of seldom used virtual memory to disk, improving overall performance.
Quote:
Doing vmstat for 30 minutes, did not see any counters jump for si/so, pi/po, and SR (all 0s) ?
Could i have some kind of spike @ certain timing (using up all the free ram), and cause the physical swap to be use ? < could this be 1 possiblity ?
The si/so counters are unlikely to move under normal circumstances but only during severe RAM shortage.
The pi/po counters move when there pagination occur. Most of that pagination might be unrelated to VM shortage, that might simply be a file being read by some process.
Th sr only move if there is RAM shortage.

A static 3G doesn't cause any activity by itself.

The most important counter to monitor is "sr". As long as it stays equal to 0, there is no RAM shortage.
You might have VM shortage though, and the vmstat column to monitor is then "swap" (available swap space).

Note also that your system might use zones configured with virtual memory capping. In such case you might have swap usage without (global) vm shortage.
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dynamic_pager(8)					    BSD System Manager's Manual 					  dynamic_pager(8)

NAME
dynamic_pager -- dynamic pager external storage manager SYNOPSIS
dynamic_pager [-F filename] [-S filesize] [-H high-water-trigger] [-L low-water-trigger] [-P priority] DESCRIPTION
The dynamic_pager daemon manages a pool of external swap files which the kernel uses to support demand paging. This pool is expanded with new swap files as load on the system increases, and contracted when the swapping resources are no longer needed. The dynamic_pager daemon also provides a notification service for those applications which wish to receive notices when the external paging pool expands or contracts. OPTIONS
-F The base name of the filename to use for the external paging files. By default this is /private/var/vm/swapfile. -S The fixed filesize [in bytes] to use for the paging files. By default dynamic_pager uses variable sized paging files, using larger sized files as paging demands increase. The -S, -H and -L options disable that default and cause dynamic_pager to use a series of fixed sized external paging files. -H If there are less than high-water-trigger bytes free in the external paging files, the kernel will signal dynamic_pager to add a new external paging file. -L If there are more than low-water-trigger bytes free in the external paging files, the kernel will coalese in-use pages and signal dynamic_pager to discard an external paging file. Low-water-trigger must be greater than high-water-trigger + filesize. -P This option is currently unimplemented. FILES
/private/var/vm/swapfile* Default external paging files. SEE ALSO
macx_swapon(2), macx_swapoff(2). Mac OS X July 8, 2003 Mac OS X
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