Messages in this thread | | | Date | Wed, 9 Jun 2004 20:32:43 +0100 | From | John Bradford <> | Subject | Re: Some thoughts about cache and swap |
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Quote from Matt Mackall <mpm@selenic.com>: > On Sun, Jun 06, 2004 at 10:38:25AM +0200, Christian Borntraeger wrote: > > John Bradford wrote: > > > Quote from Rik van Riel <riel@redhat.com>: > > > > I wonder if we should just bite the bullet and implement > > > > LIRS, ARC or CART for Linux. These replacement algorithms > > > > should pretty much detect by themselves which pages are > > > > being used again (within a reasonable time) and which pages > > > > aren't. > > > Is there really much performance to be gained from tuning the 'limited' > > > cache space, or will it just hurt as many or more systems than it helps? > > > > Thats a very good question. > > Most of the time the current algorithm works quite well. > > On the other hand, I definitely know what people mean when they complain > > about cachingand all this stuff. By just copying a big file that I dont use > > afterwards or watching an video I have 2 wonderful scenarios. > > Perhaps people should read about the referenced algorithms. LRU > (including the hybrid LRU that Linux uses) is vulnerable to > "scanning" of the sort you're describing, while the above algorithms > have varying degrees of scan-resistance. As lack of scan-resistance > seems to be "the big problem" in the current VM, this looks like an > interesting direction to go in.
Does "the big problem" really exist though?
Despite all of this discussion about swap and memory management, I _never_ reproduce any of the problems mentioned in normal use. In my experience, extreme VM problems almost always stem from mis-configured swap.
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