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    SubjectRe: [PATCH] nfs: fix congestion control
    On Tue, 2007-01-16 at 17:27 -0500, Trond Myklebust wrote:
    > On Tue, 2007-01-16 at 23:08 +0100, Peter Zijlstra wrote:
    > > Subject: nfs: fix congestion control
    > >
    > > The current NFS client congestion logic is severely broken, it marks the
    > > backing device congested during each nfs_writepages() call and implements
    > > its own waitqueue.
    > >
    > > Replace this by a more regular congestion implementation that puts a cap
    > > on the number of active writeback pages and uses the bdi congestion waitqueue.
    > >
    > > NFSv[34] commit pages are allowed to go unchecked as long as we are under
    > > the dirty page limit and not in direct reclaim.

    > What on earth is the point of adding congestion control to COMMIT?
    > Strongly NACKed.

    They are dirty pages, how are we getting rid of them when we reached the
    dirty limit?

    > Why 16MB of on-the-wire data? Why not 32, or 128, or ...

    Andrew always promotes a fixed number for congestion control, I pulled
    one from a dark place. I have no problem with a more dynamic solution.

    > Solaris already allows you to send 2MB of write data in a single RPC
    > request, and the RPC engine has for some time allowed you to tune the
    > number of simultaneous RPC requests you have on the wire: Chuck has
    > already shown that read/write performance is greatly improved by upping
    > that value to 64 or more in the case of RPC over TCP. Why are we then
    > suddenly telling people that they are limited to 8 simultaneous writes?

    min(max RPC size * max concurrent RPC reqs, dirty threshold) then?

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