On Thu, Mar 23 2006, Con Kolivas wrote:
> Jens Axboe writes:
>
> >It's a heuristic, and sometimes that will work well and sometimes it
> >will not. What if during this period of inactivity, you start bringing
> >everything in from swap again, only to page it right out because the
> >next memory hog starts running? From a logical standpoint, swap prefetch
> >and the vm must work closely together to avoid paging in things which
> >really aren't needed.
>
> If the system is idle it doesn't cost anything to bring those pages in
> (laptop mode disables any prefetching if you're thinking about power
> consumption on laptops). And if the system wants the ram that has been
> filled with prefetched pages wrongly, the prefetched pages are at the tail
> end of the inactive LRU list with a copy on backing store so if they're not
> accessed they'll be the first thing dropped in preference to anything
> else, without any I/O.
I missed the fact that you left these pages on backing store for easy
dropping in the future. I guess if you didn't, it could coarsely be
handled in user space easily.
--
Jens Axboe
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