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    SubjectRe: [PATCH 10/10] mm: per device dirty threshold
    On Tue, 24 Apr 2007 12:12:18 +0200 Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

    > 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.

    Don't think so. We call balance_dirty_pages() once per ratelimit_pages
    dirtyings and when we get there, we write 1.5*ratelimit_pages pages.

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