linux-kernel - Re: XFS vs. swsusp

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Message-ID: <20060731225308.GA4000@elf.ucw.cz>
Date:	Tue, 1 Aug 2006 00:53:08 +0200
From:	Pavel Machek <pavel@....cz>
To:	Nathan Scott <nathans@....com>
Cc:	kernel list <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, xfs@....sgi.com
Subject: Re: XFS vs. swsusp

Hi!

> > Rafael has patches to add bdev freezing to swsusp. I'd like to know if
> > they are neccessary (and why).
> > 
> > 1) Is sync() enough to guarantee that all the data written before sync
> > actually reach the platters?
> > 
> > (Or is it that data only reach the journal? OTOH that would be okay, too).
> 
> It ensures file data reaches its final resting place, and that
> metadata changes have been logged.  It does not necessarily
....

Okay, good, being safely in the journal is okay.

> > 2) If we stop all the user proceses and all the kernel threads, is
> > that enough to prevent XFS from writing to disk?
> 
> Yes, I believe so (if all user processes and kernel threads are
> stopped, who else would be left to initiate I/O?).  There is a

Well, we were afraid that you'd do it from timer interrupt or
something like that.

> timer driven wakeup done on the per-fs xfssyncd kernel threads,
> which do background metadata writeout and will write to the log
> periodically... but if those processes are all stopped too, you
> should be OK.

Timer only wakes up xfssyncd thread, right? That's okay, as that
thread will be stopped.

Rafael, I do not think we need bdev freezing changes for XFS.
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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