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

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Date:	Mon, 21 Jul 2014 16:10:27 +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!

> > > 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...
> 
> Problem is that these 76s are burned every time, whether you just use
> 500MB or the full 12TB of the machine.

On 12TB machine, how much memory is used after boot finishes? I
suspect it is not 500MB.

> Next problem is that the bitmaps are allocated (and need to be freed)
> without even being sure that a resume will happen.

Could we fix that instead? Allocating bitmaps before we see
hibernation signature is a bug.

[How long does 12TB machine boot?]

> > ...because noone sane will hibernate 12TB machine.
> 
> And Linux is only made for sane people? Thats pretty new to me ;-)

Yeah, but please don't optimize for insane people :-).

> > Yes, that's why I propose to apply just patch 6 -- to avoid soft
> > lockup warnings.
> 
> Only patch 6 would wrap the problem with the soft lockups, but the other
> patches actually improve the resume and boot situation on those
> machines.

Yeah. Provide timings for 12TB machine suspending/resuming and we may
talk about it.

#6 is bugfix. We should take it. Rest is performance improvement for
insane config. I don't think we should take it.

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