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Full Discussion: Monitoring Paging and Swapping
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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LEARN ABOUT HPUX

remote_nfs_swap

remote_nfs_swap(5)						File Formats Manual						remote_nfs_swap(5)

NAME

       remote_nfs_swap - enable swapping across NFS

VALUES

   Default
   Allowed values
DESCRIPTION

       This  tunable  controls adding a NFS filesystem for use as swap.  If is set to only local filesystems and devices can be used for swap.	If
       it is set to both local and networked file systems can be used for swap.

       Historically, this tunable was used in NFS clusters that are no longer supported, but this capability has not yet been removed.

   Who Is Expected to Change This Tunable?
       Anyone.

   Restrictions on Changing
       Changes to this tunable take effect on the next boot.

   When Should the Tunable Be Turned On?
       Almost never.  As previously mentioned, this tunable was designed for systems which are not in use  today.   Only  systems  with  extremely
       robust NFS capabilities should even consider using NFS for swap.

   What Are the Side Effects of Turning the Tunable On?
       If  the	value  is  set to and a NFS partition is added as swap, then some kernel memory will be set aside for NFS transactions to the swap
       file system.  The kernel will then use the NFS swap partition just the same as a local file system.  If the NFS capabilities of the  system
       are  not  robust,  this	could lead to extremely long swap times (both swap in and swap out), and possibly a loss of memory because all the
       reserved memory and more could be used by NFS (just when memory pressure is high) causing the need for swap.

   When Should the Tunable Be Turned Off?
       Unless you are positive that the NFS system can handle the load of being used as swap, and does not have a local file system or disk  drive
       to spare, this tunable should be set to

   What Are the Side Effects of Turning the Tunable Off?
       Any  previously	defined  NFS  swap  filesystems will no longer be allowed.  Kernel memory will not be reserved for NFS transactions due to
       swap.

   What Other Tunables Should Be Changed at the Same Time?
       None.

WARNINGS

       All HP-UX kernel tunable parameters are release specific.  This parameter may be removed or have its meaning changed in future releases	of
       HP-UX.

       Installation  of  optional  kernel  software, from HP or other vendors, may cause changes to tunable parameter values.  After installation,
       some tunable parameters may no longer be at the default or recommended values.  For information about the effects of installation  on  tun-
       able  values,  consult  the documentation for the kernel software being installed.  For information about optional kernel software that was
       factory installed on your system, see at

AUTHOR

       was developed by HP.

							     Tunable Kernel Parameters						remote_nfs_swap(5)
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