On Fri, 2007-11-09 at 17:47 +0800, Zhang, Yanmin wrote: > Comparing with 2.6.23, iozone sequential write/rewrite (512M) has 50% > regression > in kernel 2.6.24-rc1. 2.6.24-rc2 has the same regression. > > My machine has 8 processor cores and 8GB memory. > > By bisect, I located patch > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=04fbfdc14e5f48463820d6b9807daa5e9c92c51f. > > > Another behavior: with kernel 2.6.23, if I run iozone for many times after > rebooting machine, > the result looks stable. But with 2.6.24-rc1, the first run of iozone got a > very small result and > following run has 4Xorig_result.
So the second run is 4x as fast as the first run?
> What I reported is the regression of 2nd/3rd run, because first run has
> bigger regression.
So the 2nd and 3rd run are stable at 50% slower than .23?
> I also tried to change /proc/sys/vm/dirty_ratio,dirty_backgroud_ratio and
> didn't get improvement.
Could you try:
---
Subject: mm: speed up writeback ramp-up on clean systems
We allow violation of bdi limits if there is a lot of room on the
system. Once we hit half the total limit we start enforcing bdi limits
and bdi ramp-up should happen. Doing it this way avoids many small
writeouts on an otherwise idle system and should also speed up the
ramp-up.
Signed-off-by: Peter Zijlstra <[EMAIL PROTECTED]>
Reviewed-by: Fengguang Wu <[EMAIL PROTECTED]>
---
mm/page-writeback.c | 19 +++++++++++++++++--
1 file changed, 17 insertions(+), 2 deletions(-)
Index: linux-2.6/mm/page-writeback.c
===================================================================
--- linux-2.6.orig/mm/page-writeback.c 2007-09-28 10:08:33.937415368 +0200
+++ linux-2.6/mm/page-writeback.c 2007-09-28 10:54:26.018247516 +0200
@@ -355,8 +355,8 @@ get_dirty_limits(long *pbackground, long
*/
static void balance_dirty_pages(struct address_space *mapping)
{
- long bdi_nr_reclaimable;
- long bdi_nr_writeback;
+ long nr_reclaimable, bdi_nr_reclaimable;
+ long nr_writeback, bdi_nr_writeback;
long background_thresh;
long dirty_thresh;
long bdi_thresh;
@@ -376,11 +376,26 @@ static void balance_dirty_pages(struct a
get_dirty_limits(&background_thresh, &dirty_thresh,
&bdi_thresh, bdi);
+
+ nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
+ global_page_state(NR_UNSTABLE_NFS);
+ nr_writeback = global_page_state(NR_WRITEBACK);
+
bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
+
if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh)
break;
+ /*
+ * Throttle it only when the background writeback cannot
+ * catch-up. This avoids (excessively) small writeouts
+ * when the bdi limits are ramping up.
+ */
+ if (nr_reclaimable + nr_writeback <
+ (background_thresh + dirty_thresh) / 2)
+ break;
+
if (!bdi->dirty_exceeded)
bdi->dirty_exceeded = 1;
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