Messages in this thread | | | Date | Mon, 07 Apr 2003 15:24:10 +0200 | From | Helge Hafting <> | Subject | Re: An idea for prefetching swapped memory... |
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Thomas Schlichter wrote:
> What I wanted to say is that if there is free memory it should be filled with > the pages that were in use before the memory got rare. And these are the pages > swapped out last.
Not necessarily. Memory isn't merely used to hold swappable stuff, it also caches files. Consider a small but io-intensive program. The stuff you want isn't necessarily the last swap (perhaps there even isn't anything swapped out) , it might be the last thing dropped from cache instead.
And we can often predict better than "the last thing swapped/flushed" A bunch of free memory appearing could usually be better used for extra read-ahead, wether it is read-ahead of files/directories/bitmaps being accessed, or executable code faulted in from executables or swap devices.
> The other swapped out pages are swapped out even longer and so > will likely not be used in the near future... (That's what the LRU algorithm > says...)
"What we're going to need soon" is the best. It isn't always predictable, but sometimes. "The block following the last we read from some file/fs-structure" is often a good one though.
Helge Hafting
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