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Operating Systems Solaris Monitoring Paging and Swapping Post 303027334 by javanoob on Thursday 13th of December 2018 12:36:36 PM
Old 12-13-2018
Quote:
Originally Posted by jlliagre
Both the linked thread and MOS Document are correct.

vmstat is reporting that there is unused RAM and it is true. There is no data stored on that RAM.

malloc fails because there is no more swap or RAM available. All of it is either used or unused but reserved.

Let me try a metaphor: if you enter a restaurant and see many empty tables, that doesn't mean you can sit on any of them. They might all be reserved by customers that aren't there yet (and maybe some will never show up).
Hi Jilliagre,

Thanks for your reply and appreciate the suiting metaphor used.

I think the point I am trying to confirm is

a) when doing memory reservation on virtual swap, the "physical space" that is reserved on the ram/swap device is not physically allocated right ? (still show as free in vmstat and swap -l)

b) can reserved but unused memory/swap (aka virtual swap) still be use for actual physical swapping ? (or it is reserved and no longer available for other usage)

c) if reserved swap isn't reflected as used space in swap -l, does this means i am really having actual swapping if i am seeing 2GB of physical swap space being used in swap -l ?
But again, I still has free memory - when doing echo ::memstat | mdb -k, will "reserved" but unused ram, shows up in "Free" ?


Regards,
Noob
 

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SWAPON(8)						     Linux Programmer's Manual							 SWAPON(8)

NAME
swapon, swapoff - enable/disable devices and files for paging and swapping SYNOPSIS
/sbin/swapon [-h -V] /sbin/swapon -a [-v] [-e] /sbin/swapon [-v] [-p priority] specialfile ... /sbin/swapon [-s] /sbin/swapoff [-h -V] /sbin/swapoff -a /sbin/swapoff specialfile ... DESCRIPTION
Swapon is used to specify devices on which paging and swapping are to take place. Calls to swapon normally occur in the system multi-user initialization file /etc/rc making all swap devices available, so that the paging and swapping activity is interleaved across several devices and files. Normally, the first form is used: -h Provide help -V Display version -s Display swap usage summary by device. Equivalent to "cat /proc/swaps". Not available before Linux 2.1.25. -a All devices marked as ``swap'' swap devices in /etc/fstab are made available. Devices that are already running as swap are silently skipped. -e When -a is used with swapon, -e makes swapon silently skip devices that do not exist. -p priority Specify priority for swapon. This option is only available if swapon was compiled under and is used under a 1.3.2 or later kernel. priority is a value between 0 and 32767. See swapon(2) for a full description of swap priorities. Add pri=value to the option field of /etc/fstab for use with swapon -a. Swapoff disables swapping on the specified devices and files. When the -a flag is given, swapping is disabled on all known swap devices and files (as found in /proc/swaps or /etc/fstab). NOTE
You should not use swapon on a file with holes. Swap over NFS may not work. SEE ALSO
swapon(2), swapoff(2), fstab(5), init(8), mkswap(8), rc(8), mount(8) FILES
/dev/hd?? standard paging devices /dev/sd?? standard (SCSI) paging devices /etc/fstab ascii filesystem description table HISTORY
The swapon command appeared in 4.0BSD. Linux 1.x 25 September 1995 SWAPON(8)
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