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    SubjectRe: [PATCH] improve the performance of large sequential write NFS workloads

    * Steve Rago <> wrote:

    > On Fri, 2009-12-18 at 20:41 +0100, Ingo Molnar wrote:
    > > * Steve Rago <> wrote:
    > >
    > > > > Also, I don't think this needs to have a sysctl, it should just work.
    > > >
    > > > The sysctl is a *good thing* in that it allows the eager writeback behavior
    > > > to be tuned and shut off if need be. I can only test the changes on a
    > > > finite set of systems, so better safe than sorry.
    > >
    > > This issue has been settled many years ago and that's not what we do in the
    > > Linux kernel. We prefer patches to core code where we are reasonably sure they
    > > result in good behavior - and then we fix bugs in the new behavior, if any.
    > >
    > > (Otherwise odd sysctls would mushroom quickly and the system would become
    > > untestable in practice.)
    > >
    > > Ingo
    > I don't disagree, but "that's not what we do" hardly provides insight into
    > making the judgment call. [...]

    I gave you an example of the problems that arise, see the last sentence above.

    > [...] In this case, the variety of combinations of NFS server speed, NFS
    > client speed, transmission link speed, client memory size, and server memory
    > size argues for a tunable parameter, because one value probably won't work
    > well in all combinations. Making it change dynamically based on these
    > parameters is more complicated than these circumstances call for, IMHO.

    So having crappy tunables is the reason to introduce even more tunables? I
    think you just gave a good second example of why we dont want sysctls for
    features like this.


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