On Wed, 2010-11-17 at 12:27 +0800, Wu Fengguang wrote: > plain text document attachment > (writeback-speedup-per-bdi-threshold-ramp-up.patch) > Reduce the dampening for the control system, yielding faster > convergence. > > Currently it converges at a snail's pace for slow devices (in order of > minutes). For really fast storage, the convergence speed should be fine. > > It makes sense to make it reasonably fast for typical desktops. > > After patch, it converges in ~10 seconds for 60MB/s writes and 4GB mem. > So expect ~1s for a fast 600MB/s storage under 4GB mem, or ~4s under > 16GB mem, which seems reasonable. > > $ while true; do grep BdiDirtyThresh /debug/bdi/8:0/stats; sleep 1; done > BdiDirtyThresh: 0 kB > BdiDirtyThresh: 118748 kB > BdiDirtyThresh: 214280 kB > BdiDirtyThresh: 303868 kB > BdiDirtyThresh: 376528 kB > BdiDirtyThresh: 411180 kB > BdiDirtyThresh: 448636 kB > BdiDirtyThresh: 472260 kB > BdiDirtyThresh: 490924 kB > BdiDirtyThresh: 499596 kB > BdiDirtyThresh: 507068 kB > ... > DirtyThresh: 530392 kB > > CC: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> > CC: Richard Kennedy <richard@xxxxxxxxxxxxxxx> > Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> > --- > mm/page-writeback.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > --- linux-next.orig/mm/page-writeback.c 2010-11-15 13:08:16.000000000 +0800 > +++ linux-next/mm/page-writeback.c 2010-11-15 13:08:28.000000000 +0800 > @@ -125,7 +125,7 @@ static int calc_period_shift(void) > else > dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) / > 100; > - return 2 + ilog2(dirty_total - 1); > + return ilog2(dirty_total - 1) - 1; > } > > /* You could actually improve upon this now that you have per-bdi bandwidth estimations, simply set the period to (seconds * bandwidth) to get convergence in @seconds. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
