Date: Wed, 20 Sep 2017 17:36:27 +0200
From: Jan Kara <jack@suse.cz>
To: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, hannes@cmpxchg.org,
        clm@fb.com
Subject: Re: [PATCH 5/6] fs-writeback: move nr_pages == 0 logic to one
 location
Message-ID: <20170920153627.GI11106@quack2.suse.cz>
References: <1505850787-18311-1-git-send-email-axboe@kernel.dk>
 <1505850787-18311-6-git-send-email-axboe@kernel.dk>
 <20170920144159.GF11106@quack2.suse.cz>
 <33ba51dc-cb93-ad8c-d973-41ac12cb9e90@kernel.dk>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <33ba51dc-cb93-ad8c-d973-41ac12cb9e90@kernel.dk>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1533
Lines: 48

On Wed 20-09-17 09:05:51, Jens Axboe wrote:
> On 09/20/2017 08:41 AM, Jan Kara wrote:
> > On Tue 19-09-17 13:53:06, Jens Axboe wrote:
> >> Now that we have no external callers of wb_start_writeback(),
> >> we can move the nr_pages == 0 logic into that function.
> >>
> >> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> > 
> > ...
> > 
> >> +static unsigned long get_nr_dirty_pages(void)
> >> +{
> >> +	return global_node_page_state(NR_FILE_DIRTY) +
> >> +		global_node_page_state(NR_UNSTABLE_NFS) +
> >> +		get_nr_dirty_inodes();
> >> +}
> >> +
> >>  static void wb_start_writeback(struct bdi_writeback *wb, long nr_pages,
> >>  			       bool range_cyclic, enum wb_reason reason)
> >>  {
> >> @@ -942,6 +953,12 @@ static void wb_start_writeback(struct bdi_writeback *wb, long nr_pages,
> >>  		return;
> >>  
> >>  	/*
> >> +	 * If someone asked for zero pages, we write out the WORLD
> >> +	 */
> >> +	if (!nr_pages)
> >> +		nr_pages = get_nr_dirty_pages();
> >> +
> > 
> > So for 'wb' we have a better estimate of the amount we should write - use
> > wb_stat_sum(wb, WB_RECLAIMABLE) statistics - that is essentially dirty +
> > unstable_nfs broken down to bdi_writeback.
> 
> I don't mind making that change, but I think that should be a separate
> patch. We're using get_nr_dirty_pages() in existing locations where
> we have the 'wb', like in wb_check_old_data_flush().

Good point and fully agreed. So you can add:

Reviewed-by: Jan Kara <jack@suse.cz>

for this patch.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR