Re: XFS vs. swsusp

From: Pavel Machek
Date: Mon Jul 31 2006 - 18:54:23 EST


> > 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.
(cesky, pictures)
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