Messages in this thread | | | Date | Thu, 29 Apr 2004 13:47:44 -0700 | From | "Brett E." <> | Subject | Re: ~500 megs cached yet 2.6.5 goes into swap hell |
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William Lee Irwin III wrote:
> 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. > > 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.
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