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SubjectRe: 2.1.91 swap performance: jerky.


On Sat, 28 Mar 1998, Itai Nahshon wrote:
> >
> > If the page is never used again, it will never be paged in: an exit of the
> > process will just free up the page on disk, and a "fork()" will duplicate
> > the pointer to the disk rather than page it in in order to duplicate it.
>
> I did not phrase my question right...
> Suppose a page was swapped out, but the physical memory that it occupied
> was not used for something else. Now the process page-faults in that
> address. Can the page be reclaimed from memory (the data is still
> in the main memory?) or do we need to page-in from disk?

We will currently page-in. What you're asking for is essentially the
reverse of the swap cache, and yes, we'll probably do it some day (Stephen
Tweedie and some others have been working on this).

The main problem as far as I see is that while the pages can be quickly
free'd when required, the fragmentation worries me. It needs to be
integrated with the buddy system somehow (ie it should coalesce using the
buddy system, but we could then re-extract the page when required. Or
something).

Linus


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