From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kara Subject: Re: [PATCH 2/4] writeback: avoid duplicate balance_dirty_pages_ratelimited() calls Date: Wed, 13 Apr 2011 23:53:07 +0200 Message-ID: <20110413215307.GD4648@quack.suse.cz> References: <20110413085937.981293444@intel.com> <20110413090415.511675208@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andrew Morton , Peter Zijlstra , Jan Kara , Dave Chinner , Hugh Dickins , Rik van Riel , LKML , Linux Memory Management List , linux-fsdevel@vger.kernel.org To: Wu Fengguang Return-path: Content-Disposition: inline In-Reply-To: <20110413090415.511675208@intel.com> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org On Wed 13-04-11 16:59:39, Wu Fengguang wrote: > When dd in 512bytes, balance_dirty_pages_ratelimited() could be called 8 > times for the same page, but obviously the page is only dirtied once. > > Fix it with a (slightly racy) PageDirty() test. > > Signed-off-by: Wu Fengguang > --- > mm/filemap.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > --- linux-next.orig/mm/filemap.c 2011-04-13 16:46:01.000000000 +0800 > +++ linux-next/mm/filemap.c 2011-04-13 16:47:26.000000000 +0800 > @@ -2313,6 +2313,7 @@ static ssize_t generic_perform_write(str > long status = 0; > ssize_t written = 0; > unsigned int flags = 0; > + unsigned int dirty; > > /* > * Copies from kernel address space cannot fail (NFSD is a big user). > @@ -2361,6 +2362,7 @@ again: > pagefault_enable(); > flush_dcache_page(page); > > + dirty = PageDirty(page); This isn't completely right as we sometimes dirty the page in ->write_begin() (see e.g. block_write_begin() when we allocate blocks under an already uptodate page) and in such cases we would not call balance_dirty_pages(). So I'm not sure we can really do this optimization (although it's sad)... > mark_page_accessed(page); > status = a_ops->write_end(file, mapping, pos, bytes, copied, > page, fsdata); > @@ -2387,7 +2389,8 @@ again: > pos += copied; > written += copied; > > - balance_dirty_pages_ratelimited(mapping); > + if (!dirty) > + balance_dirty_pages_ratelimited(mapping); > > } while (iov_iter_count(i)); Honza -- Jan Kara SUSE Labs, CR -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org