Messages in this thread | | | Date | Thu, 18 Aug 2011 22:06:37 -0400 | From | Vivek Goyal <> | Subject | Re: [PATCH 5/5] writeback: IO-less balance_dirty_pages() |
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On Tue, Aug 16, 2011 at 10:20:11AM +0800, Wu Fengguang wrote:
[..] > + if (dirty_exceeded && !bdi->dirty_exceeded) > bdi->dirty_exceeded = 1; > > bdi_update_bandwidth(bdi, dirty_thresh, background_thresh, > nr_dirty, bdi_thresh, bdi_dirty, > start_time); > > - /* Note: nr_reclaimable denotes nr_dirty + nr_unstable. > - * Unstable writes are a feature of certain networked > - * filesystems (i.e. NFS) in which data may have been > - * written to the server's write cache, but has not yet > - * been flushed to permanent storage. > - * Only move pages to writeback if this bdi is over its > - * threshold otherwise wait until the disk writes catch > - * up. > - */ > - trace_balance_dirty_start(bdi); > - if (bdi_nr_reclaimable > task_bdi_thresh) { > - pages_written += writeback_inodes_wb(&bdi->wb, > - write_chunk); > - trace_balance_dirty_written(bdi, pages_written); > - if (pages_written >= write_chunk) > - break; /* We've done our duty */ > + if (unlikely(!writeback_in_progress(bdi))) > + bdi_start_background_writeback(bdi); > + > + base_rate = bdi->dirty_ratelimit; > + pos_ratio = bdi_position_ratio(bdi, dirty_thresh, > + background_thresh, nr_dirty, > + bdi_thresh, bdi_dirty); > + if (unlikely(pos_ratio == 0)) { > + pause = MAX_PAUSE; > + goto pause; > } > + task_ratelimit = (u64)base_rate * > + pos_ratio >> RATELIMIT_CALC_SHIFT;
Hi Fenguaang,
I am little confused here. I see that you have already taken pos_ratio into account in bdi_update_dirty_ratelimit() and wondering why to take that into account again in balance_diry_pages().
We calculated the pos_rate and balanced_rate and adjusted the bdi->dirty_ratelimit accordingly in bdi_update_dirty_ratelimit().
So why are we adjusting this pos_ratio() adjusted limit again with pos_ratio(). Doesn't it become effectively following (assuming one is decreasing the dirty rate limit).
base_rate = bdi->dirty_ratelimit pos_rate = base_rate * pos_ratio();
write_bw balance_rate = pos_rate * -------- dirty_bw
delta = max(pos_rate, balance_rate) bdi->dirty_ratelimit = bdi->dirty_ratelimit - delta;
task_ratelimit = bdi->dirty_ratelimit * pos_ratio().
So we have already taken into account pos_ratio() while calculating new bdi->dirty_ratelimit. Do we need to take that into account again.
Thanks Vivek
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