linux-kernel - Re: [RFC][PATCH -mm 2/5] swsusp: Use memory bitmaps during resume

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Message-ID: <20060809113335.GP3308@elf.ucw.cz>
Date:	Wed, 9 Aug 2006 13:33:35 +0200
From:	Pavel Machek <pavel@...e.cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	LKML <linux-kernel@...r.kernel.org>, Linux PM <linux-pm@...l.org>
Subject: Re: [RFC][PATCH -mm 2/5] swsusp: Use memory bitmaps during resume

Hi!

> > Okay, I'm little out of time now, and I do not understand 2 and 3 in
> > the series.
> 
> Well ...
> 
> > > Make swsusp use memory bitmaps to store its internal information during the
> > > resume phase of the suspend-resume cycle.
> > > 
> > > If the pfns of saveable pages are saved during the suspend phase instead of
> > > the kernel virtual addresses of these pages, we can use them during the resume
> > > phase directly to set the corresponding bits in a memory bitmap.  Then, this
> > > bitmap is used to mark the page frames corresponding to the pages that were
> > > saveable before the suspend (aka "unsafe" page frames).
> > > 
> > > Next, we allocate as many page frames as needed to store the entire suspend
> > > image and make sure that there will be some extra free "safe" page frames for
> > > the list of PBEs constructed later.  Subsequently, the image is loaded and,
> > > if possible, the data loaded from it are written into their "original" page frames
> > > (ie. the ones they had occupied before the suspend).  The image data that
> > > cannot be written into their "original" page frames are loaded into "safe" page
> > > frames and their "original" kernel virtual addresses, as well as the addresses
> > > of the "safe" pages containing their copies, are stored in a list of PBEs.
> > > Finally, the list of PBEs is used to copy the remaining image data into their
> > > "original" page frames (this is done atomically, by the architecture-dependent
> > > parts of swsusp).
> > 
> > So... if page in highmem is allocated during resume, you'll still need
> > to copy it during assembly "atomic copy", right?
> 
> No.  It can be copied before the assembly gets called, because we are in the
> kernel at that time which certainly is not in the highmem. :-)

Ahha, okay, nice trick.

> > Unfortunately, our assembler parts can't do it just now...?
> 
> No, they can't, but that just isn't necessary.  During the resume we create
> two lists of PBEs - one for "normal" pages, and one for highmem pages.  The
> first one is handled by the "atomic copy" code as usual, but the second one
> may be handled by some C code a bit earlier.

I'm still not sure if highmem support is worth the complexity -- I
hope highmem dies painful death in next 3 weeks or so.

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