From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] Add block device speciffic splice write method
Date: Thu, 23 Oct 2008 00:03:15 -0700
Message-ID: <20081023000315.6aa579f2.akpm@linux-foundation.org>
References: <1224424858-3927-1-git-send-email-dmonakhov@openvz.org>
	<20081020174931.GH19428@kernel.dk>
	<20081020181156.GI19428@kernel.dk>
	<20081022223928.a6ce476f.akpm@linux-foundation.org>
	<20081023062921.GQ22217@kernel.dk>
	<20081022234157.33d46459.akpm@linux-foundation.org>
	<20081023065113.GU22217@kernel.dk>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Cc: Dmitri Monakhov <dmonakhov@openvz.org>,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
To: Jens Axboe <jens.axboe@oracle.com>
Return-path: <linux-fsdevel-owner@vger.kernel.org>
Received: from smtp1.linux-foundation.org ([140.211.169.13]:53095 "EHLO
	smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK)
	by vger.kernel.org with ESMTP id S1751970AbYJWHD5 (ORCPT
	<rfc822;linux-fsdevel@vger.kernel.org>);
	Thu, 23 Oct 2008 03:03:57 -0400
In-Reply-To: <20081023065113.GU22217@kernel.dk>
Sender: linux-fsdevel-owner@vger.kernel.org
List-ID: <linux-fsdevel.vger.kernel.org>

On Thu, 23 Oct 2008 08:51:13 +0200 Jens Axboe <jens.axboe@oracle.com> wrote:

> On Wed, Oct 22 2008, Andrew Morton wrote:
> > On Thu, 23 Oct 2008 08:29:23 +0200 Jens Axboe <jens.axboe@oracle.com> wrote:
> > 
> > > > But really it'd be better if the throttling happened down in
> > > > pipe_to_file(), on a per-page basis.  As it stands we can dirty an
> > > > arbitrary number of pagecache pages without throttling.  I think?
> > > 
> > > That's pretty exactly why it isn't done in the actor, to avoid doing it
> > > per-page. As it's going to be PIPE_BUFFERS (16) pages max, I think this
> > > is better.
> > > 
> > > Back in the splice early days, the balance_dirty_pages() actually showed
> > > up in profiles when it was done on a per-page basis. So I'm reluctant to
> > > change it :-)
> > 
> > That's why (the misnamed) balance_dirty_pages_ratelimited() exists?
> 
> I think that is what was used, but the details are a little hazy at this
> point. So I can't say for sure.

All that function does is to bump a per-cpu variable and
once-per-thousand or so it does the balance.  If it was causing
problems in the splice application we want to know, because write()
uses it!

>  In this case it's moot anyway, since we can kill it.

Nope, we can only remove it if the fd is O_SYNC||is_sync().