Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754859AbZIJBmL (ORCPT ); Wed, 9 Sep 2009 21:42:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754815AbZIJBmK (ORCPT ); Wed, 9 Sep 2009 21:42:10 -0400 Received: from mga14.intel.com ([143.182.124.37]:44254 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753950AbZIJBmJ (ORCPT ); Wed, 9 Sep 2009 21:42:09 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.44,271,1249282800"; d="scan'208";a="185966581" Date: Thu, 10 Sep 2009 09:42:01 +0800 From: Wu Fengguang To: Jan Kara Cc: Andrew Morton , Jens Axboe , Dave Chinner , Chris Mason , Peter Zijlstra , Christoph Hellwig , Artem Bityutskiy , LKML , "linux-fsdevel@vger.kernel.org" Subject: Re: [RFC][PATCH 7/7] writeback: balance_dirty_pages() shall write more than dirtied pages Message-ID: <20090910014201.GB10957@localhost> References: <20090909145141.293229693@intel.com> <20090909150601.159061863@intel.com> <20090909154413.GC7949@duck.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090909154413.GC7949@duck.suse.cz> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3531 Lines: 85 On Wed, Sep 09, 2009 at 11:44:13PM +0800, Jan Kara wrote: > On Wed 09-09-09 22:51:48, Wu Fengguang wrote: > > Some filesystem may choose to write much more than ratelimit_pages > > before calling balance_dirty_pages_ratelimited_nr(). So it is safer to > > determine number to write based on real number of dirtied pages. > > > > The increased write_chunk may make the dirtier more bumpy. This is > > filesystem writers' duty not to dirty too much at a time without > > checking the ratelimit. > I don't get this. balance_dirty_pages_ratelimited_nr() is called when we > dirty the page, not when we write it out. So a problem would only happen if > filesystem dirties pages by set_page_dirty() and won't call > balance_dirty_pages_ratelimited_nr(). But e.g. generic_perform_write() > and do_wp_page() takes care of that. So where's the problem? It seems that btrfs_file_write() is writing in chunks of up to 1024-pages (1024 is the computed nrptrs value in a 32bit kernel). And it calls balance_dirty_pages_ratelimited_nr() each time it dirtied such a chunk. Thanks, Fengguang > > --- > > mm/page-writeback.c | 13 +++++++------ > > 1 file changed, 7 insertions(+), 6 deletions(-) > > > > --- linux.orig/mm/page-writeback.c 2009-09-09 21:19:21.000000000 +0800 > > +++ linux/mm/page-writeback.c 2009-09-09 21:25:45.000000000 +0800 > > @@ -44,12 +44,12 @@ static long ratelimit_pages = 32; > > /* > > * When balance_dirty_pages decides that the caller needs to perform some > > * non-background writeback, this is how many pages it will attempt to write. > > - * It should be somewhat larger than RATELIMIT_PAGES to ensure that reasonably > > + * It should be somewhat larger than dirtied pages to ensure that reasonably > > * large amounts of I/O are submitted. > > */ > > -static inline long sync_writeback_pages(void) > > +static inline long sync_writeback_pages(unsigned long dirtied) > > { > > - return ratelimit_pages + ratelimit_pages / 2; > > + return dirtied + dirtied / 2; > > } > > > > /* The following parameters are exported via /proc/sys/vm */ > > @@ -476,7 +476,8 @@ get_dirty_limits(unsigned long *pbackgro > > * If we're over `background_thresh' then pdflush is woken to perform some > > * writeout. > > */ > > -static void balance_dirty_pages(struct address_space *mapping) > > +static void balance_dirty_pages(struct address_space *mapping, > > + unsigned long write_chunk) > > { > > long nr_reclaimable, bdi_nr_reclaimable; > > long nr_writeback, bdi_nr_writeback; > > @@ -484,7 +485,6 @@ static void balance_dirty_pages(struct a > > unsigned long dirty_thresh; > > unsigned long bdi_thresh; > > unsigned long pages_written = 0; > > - unsigned long write_chunk = sync_writeback_pages(); > > > > struct backing_dev_info *bdi = mapping->backing_dev_info; > > > > @@ -638,9 +638,10 @@ void balance_dirty_pages_ratelimited_nr( > > p = &__get_cpu_var(bdp_ratelimits); > > *p += nr_pages_dirtied; > > if (unlikely(*p >= ratelimit)) { > > + ratelimit = sync_writeback_pages(*p); > > *p = 0; > > preempt_enable(); > > - balance_dirty_pages(mapping); > > + balance_dirty_pages(mapping, ratelimit); > > return; > > } > > preempt_enable(); > > > > -- > > > -- > Jan Kara > SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/