Re: filecache/swapcache questions

["Stephen C. Tweedie" <sct@redhat.com>]

Hi,

On Tue, 15 Jun 1999 09:32:19 +0200 (CEST), Rik van Riel
<riel@nl.linux.org> said:

>> How will it be possible for a page to be in the swapcache, for its
>> reference count to be 1 (which has been checked just before), and for
>> its swap_count(page->offset) to also be 1? I can see this being
>> possible only if an unmap/exit path might lazily leave a anonymous
>> page in the swap cache, but I don't believe that happens.

> It does happen. We use a 'two-stage' reclamation process instead
> of page aging. It seems to work wonderfully -- nice page aging
> properties without the overhead. 

Much more than that: if we take a write fault to a page which is shared
on swap by two processes, then we bring it into cache and take a
copy-on-write, leaving one copy in the swap cache (reference one: it is
_only_ in use by the swap cache now), and the other copy being reference
by the faulting process.

--Stephen
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