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    SubjectRe: [PATCH] nfs: fix congestion control
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    On Wed, 2007-01-17 at 08:50 -0500, Trond Myklebust wrote:
    > On Wed, 2007-01-17 at 09:49 +0100, Peter Zijlstra wrote:
    > > > They are certainly _not_ dirty pages. They are pages that have been
    > > > written to the server but are not yet guaranteed to have hit the disk
    > > > (they were only written to the server's page cache). We don't care if
    > > > they are paged in or swapped out on the local client.
    > > >
    > > > \All the COMMIT does, is to ask the server to write the data from its
    > > > page cache onto disk. Once that has been done, we can release the pages.
    > > > If the commit fails, then we iterate through the whole writepage()
    > > > process again. The commit itself does, however, not even look at the
    > > > page data.
    > >
    > > Thou art correct from an NFS point of view, however for the VM they are
    > > (still) just dirty pages and we need shed them.
    > >
    > > You talk of swapping them out, they are filecache pages not swapcache
    > > pages. The writepage() process needs to complete and that entails
    > > committing them.
    >
    > My point is that we can and should collect as many of the little buggers
    > as we can and treat them with ONE commit call. We don't look at the
    > data, we don't lock the pages, we don't care what the VM is doing with
    > them. Throttling is not only unnecessary, it is actually a bad idea
    > since it slows up the rate at which we can free up the pages.

    Ah, OK.

    I was thinking that since the server needs to actually sync the page a
    commit might be quite expensive (timewise), hence I didn't want to flush
    too much, and interleave them with writing out some real pages to
    utilise bandwidth.

    But if you think I should just bulk commit I can do that.

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