Messages in this thread | | | Date | Tue, 01 Apr 2003 09:03:25 +1000 | From | Nick Piggin <> | Subject | Re: Delaying writes to disk when there's no need |
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Andrew Morton wrote:
>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. > Yeah something like that looks alright.
> >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. > > I didn't think of that.
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