Messages in this thread | | | Date | Sun, 5 Oct 2003 19:26:12 +0200 | Subject | Re: Idea for improving linux buffer cache behaviour | From | Helge Hafting <> |
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On Sat, Oct 04, 2003 at 10:34:58PM -0700, Mike Fedyk wrote: > On Sat, Oct 04, 2003 at 03:14:14PM -0400, Rik van Riel wrote: > > On Sat, 4 Oct 2003, David Ashley wrote: > > > > > Forgive me if this has already been thought of, or is obsolete, or is > > > just plain a bad idea, but here it is: > > > > Do you also want an answer if the kernel already does > > exactly what you are suggesting ? ;) > > > > Then why doesn't it work better? > > > > 1) Lowest access count looked at first to toss > > > 2) If access counts equal, throw out oldest first > > > > > The net result is commonly used items you very much want to remain in > > > cache always quickly get rated very highly as the system is used. > > > > Which results in exactly the behaviour you're complaining > > about ;)) > > So, you use the system, have glibc loaded, and then play a dvd, and now > glibc needs to be re-read because it's not in cache. > > Why wasn't glibc (one example) kept in cache with the streaming read from > the dvd?
There may be many reasons here, take a look at how many times the dvd contents were used. You may get a surprise there. The number ought to be 1, right? But the burner program may read smaller chunks or something, causing many references to the same block.
Also, the number-of-references approach has its own problems. Something that is used a lot for a while will stay in cache for a long while when no longer used, taking up space. That can be a problem too - i.e. run some large simulation which fill up memory for a while, and nothing else stays in cache afterwards.
Helge Hafting - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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