On Wed 07-12-11 20:08:18, Wu Fengguang wrote: > On Wed, Dec 07, 2011 at 06:53:40PM +0800, Jan Kara wrote: > > On Mon 28-11-11 21:53:41, Wu Fengguang wrote: > > > When dd in 512bytes, generic_perform_write() calls > > > balance_dirty_pages_ratelimited() 8 times for the same page, but > > > obviously the page is only dirtied once. > > Actually, for ppc where pages can be 64 KB the problem is even worse. > > Ah yes. > > > > Fix it by accounting tsk->nr_dirtied and bdp_ratelimits at page dirty time. > > I was wondering about one more thing - couldn't we rather check in > > generic_perform_write() whether the page was dirty before calling > > ->write_end and call balance_dirty_pages_ratelimited() only if it wasn't? > > Cough.. the very original version does that exactly, then you raised > some concern here: > > https://lkml.org/lkml/2011/4/13/554 > > The discussion goes on and eventually I get to the current version > that looks most acceptable in the three options. Good point. I should have researched web (or my memory) more closely ;) Thanks for the pointer - it has reminded me why using PageDirty isn't quite perfect. > > For generic_perform_write() it doesn't really matter that much since we > > do things page-by-page anyway but other callers could be more efficient... > > That's right. You can add: Acked-by: Jan Kara <jack@xxxxxxx> Honza > > > Acked-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> > > > Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> > > > --- > > > mm/page-writeback.c | 13 +++++-------- > > > 1 file changed, 5 insertions(+), 8 deletions(-) > > > > > > --- linux-next.orig/mm/page-writeback.c 2011-11-28 21:23:20.000000000 +0800 > > > +++ linux-next/mm/page-writeback.c 2011-11-28 21:23:23.000000000 +0800 > > > @@ -1239,8 +1239,6 @@ void balance_dirty_pages_ratelimited_nr( > > > if (bdi->dirty_exceeded) > > > ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10)); > > > > > > - current->nr_dirtied += nr_pages_dirtied; > > > - > > > preempt_disable(); > > > /* > > > * This prevents one CPU to accumulate too many dirtied pages without > > > @@ -1251,12 +1249,9 @@ void balance_dirty_pages_ratelimited_nr( > > > p = &__get_cpu_var(bdp_ratelimits); > > > if (unlikely(current->nr_dirtied >= ratelimit)) > > > *p = 0; > > > - else { > > > - *p += nr_pages_dirtied; > > > - if (unlikely(*p >= ratelimit_pages)) { > > > - *p = 0; > > > - ratelimit = 0; > > > - } > > > + else if (unlikely(*p >= ratelimit_pages)) { > > > + *p = 0; > > > + ratelimit = 0; > > > } > > > /* > > > * Pick up the dirtied pages by the exited tasks. This avoids lots of > > > @@ -1749,6 +1744,8 @@ void account_page_dirtied(struct page *p > > > __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE); > > > __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED); > > > task_io_account_write(PAGE_CACHE_SIZE); > > > + current->nr_dirtied++; > > > + this_cpu_inc(bdp_ratelimits); > > > } > > > } > > > EXPORT_SYMBOL(account_page_dirtied); > > > > > > > > -- > > Jan Kara <jack@xxxxxxx> > > SUSE Labs, CR -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- 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
