This is not entirely true. There is a major difference
between pages in the page cache and pages that can go
into swap. The latter kind will always be mapped inside
the address space of a program (where it gets proper
aging and stuff), while file data could be used by
doing a read() where the data never gets mapped into
the processes address space.
Now we can get severe problems with readahead when we
are evicting just read-in data because it isn't mapped,
resulting in us having to read it again and doing double
I/O with a badly performing program.
The only reason why it's better than the alternative is
because we don't do swap readahead yet...
cheers,
Rik -- slowly getting used to dvorak kbd layout...
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| Linux memory management tour guide. H.H.vanRiel@phys.uu.nl |
| Scouting Vries cubscout leader. http://www.phys.uu.nl/~riel/ |
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