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

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Message-Id: <200608091304.35746.rjw@sisk.pl>
Date:	Wed, 9 Aug 2006 13:04:35 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@...e.cz>
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,

On Wednesday 09 August 2006 12:34, Pavel Machek wrote:
> 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. :-)

> 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.

Rafael
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