Date: Mon, 24 Aug 2015 23:09:27 +0200
From: Jan Kara <jack@suse.cz>
To: Tejun Heo <tj@kernel.org>
Cc: Jan Kara <jack@suse.cz>, Dave Chinner <david@fromorbit.com>,
        Eryu Guan <eguan@redhat.com>, Jens Axboe <axboe@kernel.dk>,
        linux-kernel@vger.kernel.org, xfs@oss.sgi.com, axboe@fb.com,
        Jan Kara <jack@suse.com>, linux-fsdevel@vger.kernel.org,
        kernel-team@fb.com
Subject: Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME
 inodes
Message-ID: <20150824210927.GA8823@quack.suse.cz>
References: <20150822003025.GS3902@dastard>
 <20150822044609.GM17933@dhcp-13-216.nay.redhat.com>
 <20150824011123.GA714@dastard>
 <20150824031816.GO17933@dhcp-13-216.nay.redhat.com>
 <20150824062425.GU3902@dastard>
 <20150824091959.GA2936@quack.suse.cz>
 <20150824145150.GA10029@mtj.duckdns.org>
 <20150824171144.GB27262@mtj.duckdns.org>
 <20150824190847.GA4234@quack.suse.cz>
 <20150824193242.GE28944@mtj.duckdns.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20150824193242.GE28944@mtj.duckdns.org>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1642
Lines: 39

On Mon 24-08-15 15:32:42, Tejun Heo wrote:
> Hello, Jan.
> 
> On Mon, Aug 24, 2015 at 09:08:47PM +0200, Jan Kara wrote:
> > Inode may contain writeback pages (but not dirty pages) without being on
> > any of the dirty lists. That is correct. Josef Bacik had patches to create
> 
> Hmmm... Can you please expand on how / why that happens?  It's kinda
> weird to require writeback to walk all inodes regardless of their
> dirty states.

It is inefficient, yes. But note that 'writeback' and 'dirty' states are
completely independent. Page can be in any of the !dirty & !writeback,
dirty & !writeback, !dirty & writeback, dirty & writeback states. So mixing
tracking of writeback and dirty state of an inode just makes the code even
messier.

> > a list to track inodes with pages under writeback but they clashed with
> > your patch series and they didn't get rebased yet AFAIR.
> 
> Wouldn't it make more sense to simply put them on one of the existing
> b_* lists?

Logically it just doesn't make sense because as I wrote above dirty and
writeback states are completely independent. Also you'd have to detect &
skip inodes that don't really have any dirty pages to write and all the
detection of "is there any data to write" would get more complicated. A
separate list for inodes under writeback as Josef did is IMO the cleanest
solution.

								Honza
-- 
Jan Kara <jack@suse.com>
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/