Date: Wed, 7 Dec 2005 23:23:17 +0100
From: Pavel Machek <pavel@ucw.cz>
To: Nigel Cunningham <ncunningham@cyclades.com>
Cc: Andy Isaacson <adi@hexapodia.org>, "Rafael J. Wysocki" <rjw@sisk.pl>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: swsusp performance problems in 2.6.15-rc3-mm1
Message-ID: <20051207222317.GA3204@elf.ucw.cz>
References: <20051205081935.GI22168@hexapodia.org> <20051205121728.GF5509@elf.ucw.cz> <1133791084.3872.53.camel@laptop.cunninghams> <200512052328.01999.rjw@sisk.pl> <1133832773.6360.38.camel@localhost> <20051206020626.GO22168@hexapodia.org> <1133835586.3896.33.camel@localhost> <20051206142237.GB1814@elf.ucw.cz> <1133993143.10276.257.camel@localhost>
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Hi!

> > > > Could we rework it to avoid writing clean pages out to the swsusp image,
> > > > but keep a list of those pages and read them back in *after* having
> > > > resumed?  Maybe do the /dev/initrd ('less +/once Documentation/initrd.txt'
> > > > if you're not familiar with it) trick to make the list of pages available 
> > > > to a userland helper.
> > > 
> > > The problem is that once you let userspace run, you have absolutely no
> > > control over what pages are read from or written to, and if a userspace
> > > app assumes that data is there in a page when it isn't, you have a
> > > recipe for an oops at best, and possibly for on disk
> > > corruption. Pages
> > 
> > No, that will not be a problem. You just resume system as you do now,
> > most pages will be not there. *But kernel knows it is not there*, and
> > will on-demand load them back. It will be normal userland application
> > doing readback. There's absolutely no risk of corruption.
> 
> How does the kernel know the pages aren't there? I thought for a
 > while

We evict them, as normally.

Literary:

cat /dev/pagecache-contents > /tmp/state
echo disk > /sys/power/state 	# Does shrink all memory, as usual, so
				# pages are gone, and kernel knows
				# they are gone. We are using normal
				# memory management code.
( cat `cat /tmp/delme` > /dev/null ) &

								Pavel
-- 
Thanks, Sharp!
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