Messages in this thread | | | Date | Tue, 18 Dec 2001 00:57:01 +0100 | Subject | Re: [patch] mempool-2.5.1-D2 | From | Stephan von Krawczynski <> |
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> > 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 size > > pool will run out in certain (maybe weird) conditions. If you cannot > > 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 is > 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 memtotal). 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?
Regards, Stephan
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