On Sun, 2009-09-06 at 11:55 +0800, Wu Fengguang wrote: > On Fri, Sep 04, 2009 at 07:05:30PM +0800, Richard Kennedy wrote: > > Reducing the number of times balance_dirty_pages calls global_page_state > > reduces the cache references and so improves write performance on a > > variety of workloads. > > > > 'perf stats' of simple fio write tests shows the reduction in cache > > access. > > Where the test is fio 'write,mmap,600Mb,pre_read' on AMD AthlonX2 with > > 3Gb memory (dirty_threshold approx 600 Mb) > > running each test 10 times, dropping the fasted & slowest values then > > taking > > the average & standard deviation > > > > average (s.d.) in millions (10^6) > > 2.6.31-rc8 648.6 (14.6) > > +patch 620.1 (16.5) > > > > Achieving this reduction is by dropping clip_bdi_dirty_limit as it > > rereads the counters to apply the dirty_threshold and moving this check > > up into balance_dirty_pages where it has already read the counters. > > > > Also by rearrange the for loop to only contain one copy of the limit > > tests allows the pdflush test after the loop to use the local copies of > > the counters rather than rereading them. > > > > In the common case with no throttling it now calls global_page_state 5 > > fewer times and bdi_stat 2 fewer. > > > > This version includes the changes suggested by > > Wu Fengguang <fengguang.wu@xxxxxxxxx> > > It seems that an redundant pages_written test can be reduced by > > --- linux.orig/mm/page-writeback.c 2009-09-06 11:44:39.000000000 +0800 > +++ linux/mm/page-writeback.c 2009-09-06 11:44:42.000000000 +0800 > @@ -526,10 +526,6 @@ static void balance_dirty_pages(struct a > (background_thresh + dirty_thresh) / 2) > break; > > - /* done enough? */ > - if (pages_written >= write_chunk) > - break; > - > if (!bdi->dirty_exceeded) > bdi->dirty_exceeded = 1; > > @@ -547,7 +543,7 @@ static void balance_dirty_pages(struct a > pages_written += write_chunk - wbc.nr_to_write; > /* don't wait if we've done enough */ > if (pages_written >= write_chunk) > - continue; > + break; > } > congestion_wait(BLK_RW_ASYNC, HZ/10); > } > > Otherwise the patch looks good to me. Thank you for the nice work! > > Reviewed-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> > Thank you. I'll give your suggestion a try & run some tests. I think you're right it should be better. Not re-reading the global counters again should be of some benefit! regards Richard -- 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
