linux-kernel - Re: [RFC][PATCH -mm] PM: Do not sync from within the freezer during suspend to RAM

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Date:	Thu, 5 Jul 2007 13:28:49 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	nigel@...pend2.net
Cc:	Pavel Machek <pavel@....cz>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Oliver Neukum <oliver@...kum.org>,
	Paul Mackerras <paulus@...ba.org>,
	Miklos Szeredi <miklos@...redi.hu>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC][PATCH -mm] PM: Do not sync from within the freezer during suspend to RAM

On Thursday, 5 July 2007 00:52, Nigel Cunningham wrote:
> Hi.
> 
> On Thursday 05 July 2007 08:49:42 Pavel Machek wrote:
> > On Thu 2007-07-05 08:48:15, Nigel Cunningham wrote:
> > > Hi.
> > > 
> > > On Thursday 05 July 2007 00:58:58 Rafael J. Wysocki wrote:
> > > > From: Rafael J. Wysocki <rjw@...k.pl>
> > > > 
> > > > The syncing of filesystems from within the freezer in not needed for 
> suspend 
> > > to
> > > > RAM.  Change freeze_processes() so that it doesn't execute sys_sync() 
> and
> > > > introduce the "syncing" version of it to be called from the hibernation 
> code
> > > > paths.
> > > > 
> > > > Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
> > > > ---
> > > >  include/linux/freezer.h |   14 ++++++++++++--
> > > >  kernel/power/disk.c     |    2 +-
> > > >  kernel/power/main.c     |    6 ++++++
> > > >  kernel/power/process.c  |    8 +++++---
> > > >  kernel/power/user.c     |    2 +-
> > > >  5 files changed, 25 insertions(+), 7 deletions(-)
> > > 
> > > Looks ok, except that I wonder if you want the following fragment. It 
> looks to 
> > > me (looking at rc6) like with this code, you'll currently call sys_sync 
> twice 
> > > when suspending to ram. Maybe I'm misreading it. Also, shouldn't it be 
> done 
> > > after taking the mutex?
> > 
> > sys_sync() should be okay to call, mutex or not.
> 
> Yeah. That wasn't my point, sorry. Calling sys_sync is pointless if you're 
> going to fail to take the mutex. It makes more sense to know you've got it 
> before you start doing things related to actually suspending.

Well, that's a valid point, I'll move it under the mutex.

And why do you think it will be called twice?

Greetings,
Rafael


-- 
"Premature optimization is the root of all evil." - Donald Knuth
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