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

["Brett E." <brettspamacct@fastclick.com>]

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.