On Thu, Apr 29, 2004 at 11:05:42AM -0700, Brett E. wrote:Thanks I think it's clear now. In layman's terms, pgpgin/out relate to disk cache activity vs pswpin/out which relate to swap activity.
Anyone know what I should believe? Sar's pgpgin/s and pgpgout/s tell me that it is paging in/out from/to disk. Yet pswpin/s and pswpout/s are both 0. Swapping and paging are the same thing I believe. pgpgin/out refer to paging, pswpin/out refer to swapping. So I for one am confused.
I guess I could dig through the source but I figured someone might have encountered this disrepency in the past.
Both are to be believed. They merely describe different things.
Pagein/pageout are counts of VM-initiated IO, regardless of whether this
IO is done on filesystem-backed pages or swap-backed pages. Pagein and
pageout are used more generally to describe VM-initiated IO and don't
exclusively refer to swap IO, but also include IO to filesystems to/from
filesystem-backed memory.
Swapin/swapout are counts of swap IO only, and are considered to apply
only to IO done to swap files/devices to/from swap-backed anonymous memory.
Pagein/pageout are both proper and necessary to have. In fact, you were
requesting that filesystem IO be done preferentially to swap IO, and the
pagein/pageout indicators showing IO while swapin/swapout indicators show
none mean you are getting exactly what you asked for.