RE: Speeding up swap
David Schwartz (davids@webmaster.com)
Sat, 23 Oct 1999 14:03:20 -0700
> > This can cause major problems if the cache is churning. The
> page could be
> > discarded instants after it was read, before you had a chance to use it.
> > This is closer to what you really want, but still not quite right.
>
> Ok. You are right. Maybe "try_to_readahead" should be extended to keep
> track of backwards (or forwards if the user reading backwards) usage, as
> it does now for forward usage. This way, you keep track of an "active
> window" within the file, and the rest can be treated as "use me first",
> keeping the cache-trashing footprint of the app to the window-size.
What I was trying to point out is that this is not as simple a thing as it
first seems. Other possibilities include limiting the amount of a cache a
particular file can occupy, but then it becomes difficult to track this in
an LRU fashion.
It's both hard to state what you want, and hard to find a way that's easy
to implement. It's also hard to come up with solutions that don't require
ugly things across kernel layers.
DS
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