Date: Fri, 3 Feb 2006 14:16:02 +0100
From: Pavel Machek <pavel@ucw.cz>
To: Nigel Cunningham <nigel@suspend2.net>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>, Pekka Enberg <penberg@cs.helsinki.fi>,
       linux-kernel@vger.kernel.org
Subject: Re: [ 01/10] [Suspend2] kernel/power/modules.h
Message-ID: <20060203131602.GD2972@elf.ucw.cz>
References: <20060201113710.6320.68289.stgit@localhost.localdomain> <200602030727.48855.nigel@suspend2.net> <200602022310.40783.rjw@sisk.pl> <200602031020.46641.nigel@suspend2.net>
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On P? 03-02-06 10:20:42, Nigel Cunningham wrote:
> Hi.
> 
> On Friday 03 February 2006 08:10, Rafael J. Wysocki wrote:
> > On machines with less RAM suspend2 will probably be better
> > preformance-wise, and that may be more important than the flexibility.
> 
> Ok. So I bit the bullet and downloaded -mm4 to take a look at this interface 
> you're making, and I have a few questions:

Great, thanks.

> - It seems to be hardwired to use swap, but you talk about writing to a 
> network image above. In Suspend2, I just bmap whatever the storage is, and 
> then submit bios to read and write the data. Is anything like that possible 
> with this interface? (Could it be extended if not?)

No, it is not hardwired. There's special swap support, but you do not
need to use it.

> - Is there any way you could support doing a full image of memory with this 
> approach? Would you take patches?

Doing full image is certainly possible; it is not important if kernel
does the writing or userspace does it. Taking patches definitely
depends how they'd look like...

> - Does the data have to be transferred to userspace? Security and efficiency 
> wise, it would seem to make a lot more sense just to be telling the kernel 
> where to write things and let it do bio calls like I'm doing at the
> moment.

As far as I can see, transfering data to userspace and back does not
really cost much:

pavel@amd:~$ time head -c $[1024*1024*1024] < /dev/zero > /dev/null
0.16user 0.27system 0.43 (0m0.439s) elapsed 100.00%CPU

...2000MB/sec is the limit (thinkpad x32).
								Pavel
-- 
Thanks, Sharp!
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