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SubjectRe: [patch] mempool-2.5.1-D2
> On Mon, 17 Dec 2001, Stephan von Krawczynski wrote:
> > [...] You will obviously _not_ shoot down allocated and still used
> > bios, no matter how long they are going to take. So your fixed
> > pool will run out in certain (maybe weird) conditions. If you
> > resize (alloc additional mem from standard VM) you are just dead.
> sure, the pool will run out under heavy VM load. Will it stay empty
> forever? Nope, because all mempool users are *required* to
deallocate the
> buffer after some (reasonable) timeout. (such as IO latency.) This
> pretty much by definition. (Sure there might be weird cases like IO
> failure timeouts, but sooner or later the buffer will be returned,
and it
> will be reused.)

Hm, and where is the real-world-difference to standard VM? I mean
today your bad-ass application gets shot down by L's oom-killer and
your VM will "refill". So you're not going to die for long in the
current situation either.
I have yet to see the brilliance in mempools. I mean, for sure I can
imagine systems that are going to like it (e.g. embedded) a _lot_. But
these are far off the "standard" system profile.
I asked this several times now, and I will continue to, where is the
VM _design_ guru that explains the designed short path to drop page
caches when in need of allocable mem, regarding a system with
aggressive caching like 2.4? This _must_ exist. If it does not, the
whole issue is broken, and it is obvious that nobody will ever find an
acceptable implementation.
I turned this problem about a hundred times round now, and as far as I
can see everything comes down to the simple fact, that VM has to
_know_ the difference between a only-cached page and a _really-used_
one. And I do agree with Rik, that the only-cached pages need an aging
algorithm, probably a most-simple approach (could be list-ordering).
This should answer the question: who's dropped next?
On the other hand you have aging in the used-pages for finding out
who's swapped out next. BUT I would say that swapping should only
happen when only-cached pages are down to a minimum level (like 5% of
Forgive my simplistic approach, where are the guys to shoot me?
And where the hell is the need for mempool in this rough design idea?


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