linux-kernel - Re: [PATCH block/for-linus] writeback: flush inode cgroup wb switches instead of pinning super

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Message-ID: <20160229210614.GC17997@ZenIV.linux.org.uk>
Date:	Mon, 29 Feb 2016 21:06:15 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Tejun Heo <tj@...nel.org>
Cc:	Tahsin Erdogan <tahsin@...gle.com>, Jan Kara <jack@...e.cz>,
	Jens Axboe <axboe@...nel.dk>, cgroups@...r.kernel.org,
	Theodore Ts'o <tytso@....edu>,
	Nauman Rafique <nauman@...gle.com>,
	linux-kernel@...r.kernel.org, Jan Kara <jack@...e.com>
Subject: Re: [PATCH block/for-linus] writeback: flush inode cgroup wb
 switches instead of pinning super_block

On Mon, Feb 29, 2016 at 03:58:37PM -0500, Tejun Heo wrote:
> On Mon, Feb 29, 2016 at 08:54:28PM +0000, Al Viro wrote:
> > > This patch removes the problematic super_block pinning and instead
> > > makes generic_shutdown_super() flush in-flight wb switches.  wb
> > > switches are now executed on a dedicated isw_wq so that they can be
> > > flushed and isw_nr_in_flight keeps track of the number of in-flight wb
> > > switches so that flushing can be avoided in most cases.
> > 
> > Wait a bloody minute.  What's to prevent shrink_dcache_for_umount() from
> > dirtying more inodes, triggering more of the same?
> 
> Hmmm?  The flushing is done after shrink_dcache_for_umount() and
> sync_filesystems().  Aren't inodes supposed to stay clean after that?

s/shrink_dcache_for_umount/fsnotify_unmount_inodes/ - sorry.