Date: Mon, 20 Feb 2006 01:53:33 +0100
From: Pavel Machek <pavel@suse.cz>
To: Nigel Cunningham <nigel@suspend2.net>
Cc: Matthias Hensler <matthias@wspse.de>, Sebastian Kgler <sebas@kde.org>,
       kernel list <linux-kernel@vger.kernel.org>, rjw@sisk.pl
Subject: Re: Which is simpler? (Was Re: [Suspend2-devel] Re: [ 00/10] [Suspend2] Modules support.)
Message-ID: <20060220005333.GL15608@elf.ucw.cz>
References: <20060201113710.6320.68289.stgit@localhost.localdomain> <200602200709.17955.nigel@suspend2.net> <20060219212952.GI15311@elf.ucw.cz> <200602201025.01823.nigel@suspend2.net>
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Hi!

> > > It is a lot slower because it does all it's I/O synchronously, doesn't
> > > compress the image and throws away memory until at least half is
> > > free.
> >
> > uswsusp does compress image (20% speedup, in recent CVS) and do
> > asynchronous I/O.
> 
> Only 20? You must be doing something horribly wrong. Asynchronous

20% is speedup for compression alone, over whole suspend
process. Device suspend/resume takes lot of time in recent kernels.

> > > > > The only con I see is the complexity of the code, but then again,
> > > > > Nigel
> > > >
> > > > ..but thats a big con.
> > >
> > > It's fud. Hopefully as I post more suspend2 patches to LKML, people will
> > > see that Suspend2 is simpler than what you are planning.
> >
> > For what I'm planning, all the neccessary patches are already in -mm
> > tree. And they are *really* simple. If you can get suspend2 to 1000
> > lines of code (like Rafael did with uswsusp), we can have something to
> > talk about.
> 
> Turn it round the right way. If you can get the functionality of Suspend2 
> using userspace only, then we have something to talk about.

Only feature I can't do is "save whole pagecache"... and 14000 lines
of code for _that_ is a bit too much. I could probably patch my kernel
to dump pagecache to userspace, but I do not think it is worth the
effort.

> > > Let's be clear. uswsusp is not really moving suspend-to-disk to
> > > userspace. What it is doing is leaving everything but some code for
> > > writing the image in kernel space, and implementing ioctls to give a
> > > userspace program the ability to request that other processes be frozen,
> > > the snapshot prepared and so on. Pages in the snapshot are copied to
> > > userspace, possibly compressed or encrypted there in future, then fed
> > > back to kernel space so it can use the swap routines to do the writing.
> > > Very little of substance is being done in userspace. In short, all it's
> > > doing is adding the complexity of
> >
> > Maybe very little of substance is being done in userspace, but all the
> > uglyness can stay there. I no longer need LZF in kernel, special
> > netlink API for progress bar (progress bar naturally lives in
> > userland), no plugin infrastructure needed, etc.
> 
> And you do need?...

I do not need anything more than what is already in -mm tree.

> > If you can do suspend2 without putting stuff listed above into kernel,
> > and in acceptable ammount of code... we can see. But you should really
> > put suspend2 code into userspace, and be done with that. Feel free to
> > spam l-k a bit more, but using existing infrastructure in -mm is right
> > way to go, and it is easier, too.
> 
> It is only easier because you're not comparing apples with apples. I have no 
> desire to spam LKML with this pointless discussion, so I'm just going to get 
> on with submitting patches for review.

So please take my comments from "suspend2 review" mail into account.

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