linux-kernel - Re: [PATCH 0/6 v2] PM / Hibernate: Memory bitmap scalability improvements

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Date:	Mon, 21 Jul 2014 15:06:29 +0200
From:	Pavel Machek <pavel@....cz>
To:	Joerg Roedel <joro@...tes.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/6 v2] PM / Hibernate: Memory bitmap scalability
 improvements

Hi!

> > > The last patch adds touching the soft lockup watchdog in
> > > rtree_next_node. This is necessary because the worst case
> > > performance (all bits set in the forbidden_pages_map and
> > > free_pages_map) is the same as with the old implementation
> > > and may still cause soft lockups. Patch 6 avoids this.
> > 
> > Ok, so what about simpler patch? Just touch the watchdog?
> 
> That would just cover the problem that the bitmap data structure and the
> algorithm in swsusp_free do not scale well on bigmem machines.

And is it a problem? Hibernation of 12TB machine will take 6 hours if
you back your swap with SSDs.

Does not scale == burns additional 60 seconds of CPU time. I think we
can live with that...

...because noone sane will hibernate 12TB machine.

> > Additional 70 seconds will be lost in noise if you write 12TB of RAM
> > to (even quite fast) disk.
> 
> Sure, but you would still get the soft lockup warnings when swsusp_free
> runs in the end.

Yes, that's why I propose to apply just patch 6 -- to avoid soft
lockup warnings.

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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