From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kara Subject: Re: [PATCH 3/7] writeback: fix dirtied pages accounting on sub-page writes Date: Wed, 7 Dec 2011 11:53:40 +0100 Message-ID: <20111207105340.GF4622@quack.suse.cz> References: <20111128135338.249672012@intel.com> <20111128140513.275099009@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-fsdevel@vger.kernel.org, Jan Kara , Peter Zijlstra , Christoph Hellwig , Andrew Morton , LKML To: Wu Fengguang Return-path: Content-Disposition: inline In-Reply-To: <20111128140513.275099009@intel.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org 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. > 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? 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... Honza > Acked-by: Peter Zijlstra > Signed-off-by: Wu Fengguang > --- > 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 SUSE Labs, CR