Date: Tue, 21 Feb 2006 12:39:52 +0100
From: Pavel Machek <pavel@suse.cz>
To: Nigel Cunningham <nigel@suspend2.net>
Cc: Andy Lutomirski <luto@myrealbox.com>, Matthias Hensler <matthias@wspse.de>,
       kernel list <linux-kernel@vger.kernel.org>,
       Sebastian Kgler <sebas@kde.org>, rjw@sisk.pl
Subject: Re: Which is simpler? (Was Re: [Suspend2-devel] Re: [ 00/10] [Suspend2] Modules support.)
Message-ID: <20060221113952.GR21557@elf.ucw.cz>
References: <20060201113710.6320.68289.stgit@localhost.localdomain> <20060220094728.GD19293@kobayashi-maru.wspse.de> <43FA97D9.4070902@myrealbox.com> <200602211446.04123.nigel@suspend2.net>
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Hi!

> > > I can only speak for myself, but I want to work with my system from the
> > > moment my desktop is back.
> >
> > I Am Not A VM Hacker, but:
> >
> > What's the point of saving pagecache during suspend?  This seems like a
> > total waste.  Why don't we save a list of pages in pagecache to disk,
> > then, after resume, prefetch them all back in.  This will slow down
> > resume (extra seeks, minimized if we sort the list, and inability
> > to compress these pages), but it will speed up suspend, and it sounds
> > a lot simpler.  There's already a patch to add swap prefetching, and
> > this can't be much more complicated.
> 
> The page cache contains the process pages, among other things, so it can't all 
> be discarded with impunity. You're right in suggesting that
> discarding them 

Well, we already have perfectly good code to free pagecache.

> and then prefetching them would be a potential alternative, but it would 
> actually be more complicated: you'd still have to remember which pages you 
> wanted to fault back in, and some how store that info in the
> image. You'd 

That's okay. Imagine 

"cat /proc/vm/pagecache-contents > /tmp/delme" just before suspend and
"cat /tmp/delme | prefetcher" just after it. Prefetcher is actually
simple app that reads specified pages, then discards them. It can
actually be done in userspace around regular swsusp/uswsusp/suspend2
with no impact on it.

								Pavel

-- 
Web maintainer for suspend.sf.net (www.sf.net/projects/suspend) wanted...
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