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    SubjectRe: [PATCH 10/10] mm: per device dirty threshold
    On Sat, 21 Apr 2007 14:01:36 +0200 Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

    > On Sat, 2007-04-21 at 02:55 -0700, Andrew Morton wrote:
    >
    > > > +
    > > > + __mod_bdi_stat64(bdi, BDI_WRITEOUT, -half);
    > > > + bdi->cycles += cycle;
    > > > + }
    > > > + bdi->cycles = global_cycle;
    > > > + spin_unlock_irqrestore(&bdi->lock, flags);
    > > > +}
    > >
    > > Here we get to the real critical substance of the patchset, and I don't
    > > have a clue what it's doing nor how it's doing it. And I bet nobody else
    > > does either.
    >
    > I shall send a comment patch; but let me try to explain:
    >
    > I am trying to keep a floating proportion between the BDIs based on
    > writeout events.

    The term "writeout event" hasn't been defined. I assume that it refers to
    something like "one call to balance_dirty_pages()". Or maybe "one pass
    through balance_dirty_pages()'s inner loop". Or maybe something else.
    This is important, because the reader is already a bit lost.

    > That is, each device is given a share equal to its
    > proportion of completed writebacks

    In what units are "writebacks" measured? Pages?

    > (writeback, we are in the process of
    > writing vs. writeout, we have written). This proportion is measured in a
    > 'time'-span measured itself in writeouts.

    time is measured how? jiffies? Calls to balance_dirty_pages(), or passes
    around its inner loop, or...

    > Example:
    >
    > device A completes 4, device B completes 12 and, device C 16 writes.

    writes of what? One page??

    I think you get my point ;) Please start from the top. Define terms before
    using them, always specify in what units all things are being measured,
    assume *no* prior knowledge apart from general kernel-fu.

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