SUMMARY : swap inconsistencies

From: Steve Franks (
Date: Tue Jan 20 1998 - 17:26:33 CST

Fellow Sun managers,

I am afraid I can't post a definitive article to this list as some of
you requested but I did learn some useful things :

swap -s reports virtual swap info ie, backing store + that part of
memory which is not used for kernel, /tmp etc

* Swap is used for virtual memory pages that have vnodes NOT pointing to
a UFS inode - things like heap, shared mem etc. These are called
anonymous pages

* The use of malloc makes a reservation of swap space (see "reserved"
from swap -s) but only the actual use of the space transfers the
reservation to an actual allocation.

* There is some user control over the amount of memory kept out of swap
for the rest of the system. See Swapfs_minfree. Swapfs uses this at
startup & it is set to 2M or 1/8 total mem (whichever is larger).

* Solaris will use disk based virtual swap before is uses memory VS

* Several people were able to get their swap components to match between
swap -s & vmstat - I still cannot (even after using disk blocks AND
pages as the multiplier) - maybe I have a bug somewhere!!

* It was suggested that my /tmp could account for the discrepancies I
observed. My /tmp was only a few MB - I don't think that is the whole

For more info, try some of these : *

* Sunsolve infodoc number "14120", FAQ number 1538, Solaris
2.x Q&A document 1013, and the Sun Technical Bulletin number 1130
(chapter 6). (thanks Richard Roberto for the refs)



Thanks to :
Joseph S D Yao
Richard Roberto
Rick Kelly
Jeff Graham

Good luck to those of you, like me, that havn't got a clue!!



Steve Franks
National Australia Bank, Midrange Services

1/216 Victoria Pde ph : +61 3 9208 5794 E Melbourne, Victoria fax : +61 3 9208 5023 Australia 3150 email : =================================================

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