linux-kernel - Re: [PATCH v2 3/3] PM / hibernate: Recycle safe pages after image restoration

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Message-ID: <20160815143349.GB29447@amd>
Date:	Mon, 15 Aug 2016 16:33:49 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Linux PM list <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/3] PM / hibernate: Recycle safe pages after image
 restoration

On Thu 2016-08-11 23:23:20, Rafael J. Wysocki wrote:
> On Thursday, August 11, 2016 11:06:15 PM Pavel Machek wrote:
> > Hi!
> > 
> > > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > 
> > > One of the memory bitmaps used by the hibernation image restoration
> > > code is freed after the image has been loaded.
> > > 
> > > That is not quite efficient, though, because the memory pages used
> > > for building that bitmap are known to be safe (ie. they were not
> > > used by the image kernel before hibernation) and the arch-specific
> > > code finalizing the image restoration may need them.  In that case
> > > it needs to allocate those pages again via the memory management
> > > subsystem, check if they are really safe again by consulting the
> > > other bitmaps and so on.
> > > 
> > > To avoid that, recycle those pages by putting them into the global
> > > list of known safe pages so that they can be given to the arch code
> > > right away when necessary.
> > 
> > Ok, so you are trying to gain speed here? How much is the speedup?
> 
> This is more about making it easier to debug than about speed, TBH.
> 
> Avoiding bitmap operations and the mm subsystem involvement reduces
> complexity and the number of places to look into in case something goes
> wrong.

Well, it looked like 3/3 just added code and did not remove anything,
so I fail to see how it makes code easier to follow...

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