linux-kernel - Re: [RFC][PATCH -mm] PM: Do not sync filesystems from within the freezer

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Message-Id: <E1I6iMD-0003Gl-00@dorka.pomaz.szeredi.hu>
Date:	Fri, 06 Jul 2007 09:36:01 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	nigel@...pend2.net
CC:	miklos@...redi.hu, nigel@...pend2.net, rjw@...k.pl, pavel@....cz,
	linux-pm@...ts.linux-foundation.org, benh@...nel.crashing.org,
	linux-kernel@...r.kernel.org, mjg59@...f.ucam.org,
	oliver@...kum.org, paulus@...ba.org, mingo@...e.hu
Subject: Re: [RFC][PATCH -mm] PM: Do not sync filesystems from within the freezer

> > > To get more serious and practical though, I think the solution is to
> > > fuzz the userspace/kernelspace distinction. What we really want to
> > > do is freeze things that submit I/O, then sync, then freeze anything
> > > that processes I/O and needs to be frozen. In effect, redefine fuse
> > > processes as freezeable kernel threads.
> > 
> > Another myth, that has been debunked already.  The problem is: how do
> > you define fuse processes?  There's no theoretical or even practial
> > way to do that.
> 
> No theoretical or practical way?! I'll freely admit to being quite ignorant 
> about fuse, but surely there's some way by which they can be distinguished.

How?  OK, there are some tasks, that read and/or write /dev/fuse. And
there are some that just communicate in some way with the above.

These could all be considered "fuse tasks", but those that don't do
I/O on /dev/fuse are indistinguishable from non-fuse tasks.

And for example sshfs does have such a thread, which is in the reply
chain, yet never communicates directly with the fuse kernel module.

Miklos
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