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From: Nigel Cunningham <ncunningham@crca.org.au>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: linux-pm@lists.linux-foundation.org, linux-kernel@vger.kernel.org
Subject: Re: [linux-pm] Freezer: Don't count threads waiting for frozen	filesystems.
Date: Wed, 29 Oct 2008 10:04:14 +1100	[thread overview]
Message-ID: <1225235054.9661.37.camel@nigel-laptop> (raw)
In-Reply-To: <E1Kuv87-00064p-Lk@pomaz-ex.szeredi.hu>

Hi again.

On Tue, 2008-10-28 at 21:25 +0100, Miklos Szeredi wrote:
> On Tue, 28 Oct 2008, Nigel Cunningham wrote:
> > The answer is to freeze the fuse filesystems first, stopping new
> > requests (freezing the processes making them) before they are passed on
> > to userspace and allowing existing requests to complete or freeze. Once
> > that is done, the userspace fuse processes will be idle, at least as far
> > as fuse activity is concerned. After fuse activity is stopped, userspace
> > can be frozen without worrying about what processes are fuse and what
> > aren't. This is what my patch implements so far.
> 
> OK.
> 
> > To deal with requests that are already in progress, I'd suggest three
> > possibilities, in the order I think they should be preferred.
> > 
> > 1) Use wait_event_freezeable[_timeout] in fuse code. Probably preferable
> > to #2, but I thought of it later :)
> > 
> > 2) Use freezer_do_not_count as part of FUSE_MIGHT_FREEZE (resetting
> > before exiting the callers, of course). If the request doesn't complete
> > during the freezing period, it must be because the userspace thread was
> > already frozen. If the request does complete, we're counted again during
> > the normal freezing of userspace that follows the freezing of
> > filesystems.
> > 
> > 3) Adding a means to check whether processes being frozen are fuse
> > requests. The code could then wait for fc->num_waiting - (say)
> > fc->num_frozen == 0.
> 
> Yup, these fix the freezing of tasks which have outstanding fuse
> requests.
> 
> However it does not fix the freezing of tasks which are waiting for
> VFS locks (i.e. inode->i_mutex) held by the outstanding fuse requests.
> This is the tricky part...

Okay. Looking back on our conversation brought me back to this message,
which I think needs another reply.

If we take the strategy of holding new requests and allowing existing
ones to complete, then am I right in thinking that we only need to worry
about where inode->i_mutex is taken in fs/fuse/file.c (I don't see it
taken in other fs/fuse/*.c files).

If that's correct, dealing with that issue looks relatively straight
forward: we need some more FUSE_MIGHT_FREEZE calls for those functions,
and something done to the vfs_check_frozen call - I'm a bit confused by
that - inode->i_sb will refer to the fuse filesystem, won't it?

Regards,

Nigel


  parent reply	other threads:[~2008-10-28 23:04 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <1224886068.6478.21.camel@nigel-laptop>
2008-10-26 20:01 ` Rafael J. Wysocki
2008-10-27 11:12   ` Miklos Szeredi
2008-10-27 11:20     ` Nigel Cunningham
2008-10-27 11:37       ` Rafael J. Wysocki
2008-10-27 11:40         ` Nigel Cunningham
2008-10-27 12:38           ` Miklos Szeredi
2008-10-27 20:59             ` Nigel Cunningham
2008-10-27 21:09               ` Miklos Szeredi
2008-10-27 22:13                 ` Nigel Cunningham
2008-10-28 20:25                   ` Miklos Szeredi
2008-10-28 21:29                     ` Nigel Cunningham
2008-10-28 21:51                       ` Miklos Szeredi
2008-10-28 22:00                         ` Rafael J. Wysocki
2008-10-28 22:02                           ` Miklos Szeredi
2008-10-28 22:21                             ` Rafael J. Wysocki
2008-10-28 23:21                               ` Miklos Szeredi
2008-10-28 23:59                                 ` Rafael J. Wysocki
2008-10-29  8:10                                   ` Miklos Szeredi
2008-10-29 13:51                                     ` Alan Stern
2008-10-29 14:50                                       ` Miklos Szeredi
2008-10-29 15:28                                         ` Alan Stern
2008-10-29 15:50                                           ` Miklos Szeredi
2008-10-29 16:17                                             ` Alan Stern
2008-10-29 16:10                                           ` Miklos Szeredi
2008-10-29 20:37                                             ` Alan Stern
2008-10-29 21:11                                               ` Rafael J. Wysocki
2008-10-29 21:45                                                 ` Nigel Cunningham
2008-10-29 22:07                                                   ` Rafael J. Wysocki
2008-10-29 23:53                                                     ` Miklos Szeredi
2008-11-09 13:44                                                       ` Pavel Machek
2008-10-29 23:48                                                   ` Miklos Szeredi
2008-10-30 13:04                                                     ` Nigel Cunningham
2008-10-30 13:56                                                       ` Alan Stern
2008-10-30 21:44                                                         ` Nigel Cunningham
2008-10-31  8:49                                                           ` Miklos Szeredi
2008-10-31  9:10                                                             ` Nigel Cunningham
2008-10-31  9:16                                                               ` Miklos Szeredi
2008-10-31 11:28                                                                 ` Nigel Cunningham
2008-10-31 12:44                                                                   ` Miklos Szeredi
2008-10-31 21:11                                                                     ` Nigel Cunningham
2008-10-29 23:43                                               ` Miklos Szeredi
2008-10-30 13:54                                                 ` Alan Stern
2008-10-30 14:39                                                   ` Miklos Szeredi
2008-10-30 17:07                                                     ` Alan Stern
2008-10-30 17:43                                                       ` Miklos Szeredi
2008-10-30 20:17                                                     ` Rafael J. Wysocki
2008-11-15 16:58                                                     ` Pavel Machek
2008-10-29 23:56                                               ` Matthew Garrett
2008-10-28 22:03                         ` Nigel Cunningham
2008-10-28 23:04                     ` Nigel Cunningham [this message]
2008-10-28 23:12                       ` Miklos Szeredi
2008-10-28 23:17                         ` Nigel Cunningham
2008-10-28 23:24                           ` Miklos Szeredi
2008-10-28 23:41                             ` Nigel Cunningham
2008-10-28 23:45                               ` Miklos Szeredi
2008-10-28 23:50                                 ` Miklos Szeredi
2008-10-28 23:58                                   ` Nigel Cunningham
2008-10-28 23:54                                 ` Nigel Cunningham
2008-10-27 11:37       ` Miklos Szeredi

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