Messages in this thread | | | Date | Mon, 31 Mar 2003 14:45:00 -0800 | From | Andrew Morton <> | Subject | Re: Delaying writes to disk when there's no need |
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Nick Piggin <piggin@cyberone.com.au> wrote: > > it seems to me that > doing writeout whenever the disk would otherwise be idle > (and we have dirty memory to write out) would be a good > solution.
This is what the recently-removed BDI_read_active flag in backing_dev_info was supposed to be for. I let it go because I don't think it's terribly important and it's time to stop fiddling with the vfs writeout code and it wasn't right anyway.
Note that 2.5 starts pdflush writeout at 10% of memory dirty. Or even lower if there is a lot of mapped memory around. Whereas 2.4 will start background writeout at 30% or 40% dirty. That's a fairly significant tuning change.
The algorithm for utilisation of an idle disk should be, in balance_dirty_pages():
if (ps.nr_dirty + ps.nr_writeback < background_thresh) { if (time_after(jiffies, bdi->last_read + HZ/100)) { if (bdi->write_requests_in_flight < 2) { struct writeback_control wbc = { .bdi = bdi, .sync_mode = WB_SYNC_NONE, .nr_to_write = write_chunk, };
writeback_inodes(&wbc); } } return; }
Or something like that. It's pretty close.
It could have pretty bad failure modes. Short-lived files in /tmp now perform writeout, which needs to be waited on when those files are removed.
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