Re: ~500 megs cached yet 2.6.5 goes into swap hell

William Lee Irwin III
2004-04-29T18:32:32Z

On Thu, Apr 29, 2004 at 11:05:42AM -0700, Brett E. wrote:
> 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.

-- wli