linux-kernel - Re: [PATCH 1/1] suspend: delete sys

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Date:	Wed, 8 Jul 2015 10:40:00 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Pavel Machek <pavel@....cz>
cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Oliver Neukum <oneukum@...e.de>,
	Dave Chinner <david@...morbit.com>,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	Len Brown <len.brown@...el.com>, Len Brown <lenb@...nel.org>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 1/1] suspend: delete sys_sync()

On Wed, 8 Jul 2015, Pavel Machek wrote:

> > well, that depends on what the purpose of the sync is supposed to be.
> > 
> > If it is there to prevent users from corrupting their filesystems as a result
> > of a mistake, it is insufficient.  If it's there for other reasons, I'm wondering
> > what those reasons are (on systems that suspend and resume reliably, because the
> > original reason to put it in there was to reduce the damage from suspend/resume
> > crashes).
> 
> I put it there, and there were more reasons than "crashes" to put it
> there.
> 
> 1) crashes.
> 
> 2) battery is quite likely to run out in suspended machine.
> 
> 3) if someone pulls the stick and puts it in other machine, I wanted
> consistent filesystem at least after journal replay.

I was going to make the same points.

>From my point of view, whether to issue a sync is a tradeoff.  I can't
remember any time in the last several years where lack of a sync would
have caused a problem for my computers, but the possibility still
exists.

So on one hand, issuing the sync can help prevent a low-probability 
problem.  On the other hand, issuing the sync takes a small amount of 
time (negligible for my purposes but not negligible for Len and 
others).

I prefer to pay a very small cost to prevent a low-probability problem.  
Others may not want to pay, because to them the cost is larger or the 
probability is lower.

_That_ is the justification for not eliminating the sync completely but 
making it optional.

Alan Stern

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