Messages in this thread | | | Subject | Re: [PATCH 10/10] mm: per device dirty threshold | From | Peter Zijlstra <> | Date | Tue, 24 Apr 2007 12:12:18 +0200 |
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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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