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; } /* -- 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
