Messages in this thread | | | Subject | Re: [RFC][PATCH] mm: stop balance_dirty_pages doing too much work | From | Peter Zijlstra <> | Date | Fri, 07 Aug 2009 16:38:47 +0200 |
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On Fri, 2009-08-07 at 15:36 +0100, Richard Kennedy wrote: > On Fri, 2009-08-07 at 14:20 +0200, Peter Zijlstra wrote: > > On Wed, 2009-06-24 at 11:38 +0100, Richard Kennedy wrote: > .... > > OK, so Chris ran into this bit yesterday, complaining that he'd only get > > very few write requests and couldn't saturate his IO channel. > > > > Now, since writing out everything once there's something to do sucks for > > Richard, but only writing out stuff when we're over the limit sucks for > > Chris (since we can only be over the limit a little), the best thing > > would be to only write out when we're over the background limit. Since > > that is the low watermark we use for throttling it makes sense that we > > try to write out when above that. > > > > However, since there's a lack of bdi_background_thresh, and I don't > > think introducing one just for this is really justified. How about the > > below? > > > > Chris how did this work for you? Richard, does this make things suck for > > you again? > > > > --- > > mm/page-writeback.c | 2 +- > > 1 files changed, 1 insertions(+), 1 deletions(-) > > > > diff --git a/mm/page-writeback.c b/mm/page-writeback.c > > index 81627eb..92f42d6 100644 > > --- a/mm/page-writeback.c > > +++ b/mm/page-writeback.c > > @@ -545,7 +545,7 @@ static void balance_dirty_pages(struct address_space *mapping) > > * threshold otherwise wait until the disk writes catch > > * up. > > */ > > - if (bdi_nr_reclaimable > bdi_thresh) { > > + if (bdi_nr_reclaimable > bdi_thresh/2) { > > writeback_inodes(&wbc); > > pages_written += write_chunk - wbc.nr_to_write; > > get_dirty_limits(&background_thresh, &dirty_thresh, > > > > > I'll run some tests and let you know :) > > But what if someone has changed the vm settings? > Maybe something like > (bdi_thresh * dirty_background_ratio / dirty_ratio) > might be better ?
Yeah, but that's a mult and a div extra, all that really matters is being able to generate plenty of IO. I think the 1/2 approximation should suffice, but we'll see.
Thanks for testing.
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