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    SubjectRe: [PATCH 10/10] mm: per device dirty threshold
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    On Tue, 2007-04-24 at 03:00 -0700, Andrew Morton wrote:
    > On Tue, 24 Apr 2007 11:47:20 +0200 Miklos Szeredi <miklos@szeredi.hu> wrote:
    >
    > > > Ahh, now I see; I had totally blocked out these few lines:
    > > >
    > > > pages_written += write_chunk - wbc.nr_to_write;
    > > > if (pages_written >= write_chunk)
    > > > break; /* We've done our duty */
    > > >
    > > > yeah, those look dubious indeed... And reading back Neil's comments, I
    > > > think he agrees.
    > > >
    > > > Shall we just kill those?
    > >
    > > I think we should.
    > >
    > > Athough I'm a little afraid, that Akpm will tell me again, that I'm a
    > > stupid git, and that those lines are in fact vitally important ;)
    > >
    >
    > It depends what they're replaced with.
    >
    > That code is there, iirc, to prevent a process from getting stuck in
    > balance_dirty_pages() forever due to the dirtying activity of other
    > processes.
    >
    > hm, we ask the process to write write_chunk pages each go around the loop.
    > So if it wrote write-chunk/2 pages on the first pass it might end up writing
    > write_chunk*1.5 pages total. I guess that's rare and doesn't matter much
    > if it does happen - the upper bound is write_chunk*2-1, I think.

    Right, but I think the problem is that its dirty -> writeback, not dirty
    -> writeback completed.

    Ie. they don't guarantee progress, it could be that the total
    nr_reclaimable + nr_writeback will steadily increase due to this break.

    How about ensuring that vm_writeout_total increases least
    2*sync_writeback_pages() during our stay in balance_dirty_pages(). That
    way we have the guarantee that more pages get written out than can be
    dirtied.

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