linux-kernel - Re: Fw: Re: [mm PATCH 4/6] RCU: (now) CPU hotplug

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Message-ID: <20070130194940.GI2092@linux.vnet.ibm.com>
Date:	Tue, 30 Jan 2007 11:49:40 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Andrew Morton <akpm@...l.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, Ingo Molnar <mingo@...e.hu>,
	dipankar@...ibm.com, Gautham Shenoy <ego@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Fw: Re: [mm PATCH 4/6] RCU: (now) CPU hotplug

On Tue, Jan 30, 2007 at 10:27:18AM -0800, Andrew Morton wrote:
> On Tue, 30 Jan 2007 17:44:47 +0100
> "Rafael J. Wysocki" <rjw@...k.pl> wrote:
> 
> > > I need to look at all uses of PF_NOFREEZE -- as I understand the
> > > code, processes marked PF_NOFREEZE will continue running, potentially
> > > interfering with the hotplug operation.  :-(
> > > 
> > > I will pass my findings on to this list.
> > 
> > Well, I did it some time ago, although not very thoroughly.
> > 
> > AFAICS there are not so many, but one that stands out is the worker threads.
> > We needed two of them to actually go to sleep, so now it's possible to create
> > a "freezeable workqueue" the worker thread of which will not set PF_NOFREEZE,
> > but currently this is only used by XFS.
> 
> Or we can create a variant of freeze_processes which ignores PF_NOFREEZE.
> 
> As I said eariler, we might need to change the freezer code for this
> application.  In fact we should do so: that sys_sync() call in there is
> quite inappropriate, as is, I suppose, the two-pass freeze attempt.  As are
> the nice printks, come to that.
> 
> Pretty simple stuff though.

And we might need to change some of the processes that currently set
PF_NOFREEZE so that they periodically go somewhere that the freezer can
find them -- if I remember correctly, at least some of the PF_NOFREEZE
tasks were so marked in order to prevent suspend hangs.

Part of what I need to look at.  ;-)

							Thanx, Paul
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