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Debate on Linux Virtual Memory Handling

Posted by CmdrTaco on from the stuff-to-read dept.

xturnip sent us a good piece running over at Byte about Linux's VM. Somewhat more technical then the stuff we usually see online, this one talks about different VM systems, and the egos in the kernel. Its worth a read.

2 of 330 comments (clear)

  1. Alan will be switching VMs soon... by rakarnik · · Score: 5, Informative

    See this posting to LKML:

    Alans talking about switching VMs in -ac kernels

    --
    Genebrew
  2. Re:Make it a build option by Rik+van+Riel · · Score: 5, Informative
    I wonder what Rik has to say about the new "blessed" VM? If he thinks it's a better all-around VM, then the debate can stop pretty quickly I would think.

    Well, since you wanted to know ;)

    First let me explain that most of the time in the beginning of 2.4 was spent making the VM stable, stopping it from chrashing on highmem machines, etc... Speed improvements were a secondary thing, to do later on. Secondly, Linus is a very busy man and didn't seem to have the time even to apply critical bugfixes at times, so his kernel has had a big disadvantage over Alan's kernel.

    Around the time where the VM in Alan's kernel got stable, I was finally getting the time to work on speed improvements and Linus still lagged a few patches, suddenly Andrea surprised us all by posting the first version of his new VM online. An even bigger surprise was that Linus integrated this into the kernel within 24 hours, without even asking Andrea!

    As to why Andrea's VM is faster for desktop use ... it was optimised for speed on low to medium loads in exactly the same way the 2.2 kernel was. Note that this also means the server falls over quicker under high load and it is basically impossible to tune the system to run decently under all loads ... just like 2.2.

    My VM was slower for desktop loads, but since the thing stabilised I put in some time to make things faster and I seem to have mostly caught up with Andrea on the speed front now. The benchmark results posted on the linux-kernel mailing list seem to indicate that Andrea's VM is faster for some things, while my VM is faster for some other things.

    Personally, I think it is easier to make a solid VM fast than it would be to make a fast VM solid. This opinion was formed because of the living hell of the Linux 2.2 VM, which was undocumented and horribly subtle.

    In the future, I know I'll always be optimising for (1) maintainability, (2) correctness/stability and (3) performance, in that order...