From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757152AbXFLQDP (ORCPT ); Tue, 12 Jun 2007 12:03:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754956AbXFLQDA (ORCPT ); Tue, 12 Jun 2007 12:03:00 -0400 Received: from smtp2.linux-foundation.org ([207.189.120.14]:57427 "EHLO smtp2.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754664AbXFLQDA (ORCPT ); Tue, 12 Jun 2007 12:03:00 -0400 Date: Tue, 12 Jun 2007 09:02:30 -0700 From: Andrew Morton To: Jens Axboe Cc: Peter Zijlstra , linux-kernel@vger.kernel.org Subject: Re: splice: move balance_dirty_pages_ratelimited() outside of splice actor Message-Id: <20070612090230.19ab939c.akpm@linux-foundation.org> In-Reply-To: <20070612124449.GD18832@kernel.dk> References: <200706112159.l5BLxF5x004043@hera.kernel.org> <20070611163433.dbc541ec.akpm@linux-foundation.org> <20070612063510.GO18832@kernel.dk> <20070612112059.GY18832@kernel.dk> <20070612113101.GZ18832@kernel.dk> <1181649983.7348.309.camel@twins> <20070612121047.GB18832@kernel.dk> <1181650572.7348.312.camel@twins> <20070612124449.GD18832@kernel.dk> X-Mailer: Sylpheed 2.4.1 (GTK+ 2.8.17; x86_64-unknown-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 12 Jun 2007 14:44:50 +0200 Jens Axboe wrote: > On Tue, Jun 12 2007, Peter Zijlstra wrote: > > On Tue, 2007-06-12 at 14:10 +0200, Jens Axboe wrote: > > > On Tue, Jun 12 2007, Peter Zijlstra wrote: > > > > On Tue, 2007-06-12 at 13:31 +0200, Jens Axboe wrote: > > > > > > > > > Would you prefer this change, then? I'd prefer keeping the current code, > > > > > unless it's absolutely critical that we call > > > > > balance_dirty_pages_ratelimited() for each and every page instead of eg > > > > > every 16 pages here. > > > > > > > > For that we should call: > > > > balance_dirty_pages_ratelimited_nr(mapping, nr); > > > > > > > > Which is ok, for small nr. > > > > > > OK, then this should be better: yup, the patch looks fine, thanks. It will in practice be OK calling balance_dirty_pages() once per 16 pages but one should try to be a good little kernel citizen and do the right thing, I guess. > > > diff --git a/fs/splice.c b/fs/splice.c > > > index 25ec9c8..ed40967 100644 > > > --- a/fs/splice.c > > > +++ b/fs/splice.c > > > @@ -844,6 +883,9 @@ generic_file_splice_write_nolock(struct pipe_inode_info *pipe, struct file *out, > > > sd.file = out; > > > ret = __splice_from_pipe(pipe, &sd, pipe_to_file); > > > if (ret > 0) { > > > + unsigned long nr_pages; > > > + > > > + nr_pages = (ret + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT; > > > > perhaps? > > nr_pages = DIV_ROUND_UP(ret, PAGE_CACHE_SIZE); > > > > not sure how horrid that turns out to be; you never know with gcc. > > Well, I think such macros are horribly ugly and that the original code > is MUCH easier to read. I think the macros are pretty foul too (perhaps we should migrate it to "div_round_up()"). But we should migrate to them. Because once one has learned what a particular helper like this does, the code becomes more readable, more understandable and easier to verify correct behaviour. Whereas the open-coded arithmetic is _always_ suspect and always needs to be checked each time one's eye passes over it. And then there's the ongoing pitter-patter of "convert to DIV_ROUND_UP" patches in my inbox ;) It's not, however, our biggest problem.