From: Nigel Cunningham <ncunningham@cyclades.com>
Organization: Cyclades Corporation
To: Andreas Happe <andreashappe@snikt.net>
Subject: Re: Which is simpler? (Was Re: [Suspend2-devel] Re: [ 00/10] [Suspend2] Modules support.)
Date: Tue, 21 Feb 2006 12:57:25 +1000
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Hi.

On Tuesday 21 February 2006 10:52, Andreas Happe wrote:

[...]

> I think that 'some people, like you' may be more than you think.
>
> I tried to use suspend2, but setup wasn't that great (i.e. didn't work
> as well or easy as swsusp) so I dropped it.

Could you provide more detail? If there's something I can do to make it eas=
ier=20
to use, I'm more than willing to consider that.

[...]

> Encryption and compression for non-timecritical tasks: User or
> kernelspace? The other stuff would be driver fixes (which would be
> accepted) or infrastructure changes (rafael is at least interested in
> bdev freezing, other stuff like using bitmaps seem totaly not acceptable
> (and weren't for rather long.. but nigel didn't seem to mind)).

I'm not sure I get what you're saying I didn't seem to mind.

Your comment about using bitmaps made me do some math to see how much I'm=20
saving by using them instead of Pavel's struct pbes. I don't think they wer=
e=20
commented on as 'totally unacceptable', but as I look at them again now, I'=
m=20
not so sure they're worth the effort. Will look again a little later in the=
=20
day, particularly at the flow on effects of making such a change - perhaps=
=20
I've forgotten something else).

(For the record, my thinking went: swsusp uses n (12?) bytes of meta data f=
or=20
every page you save, where as using bitmaps makes that much closer to a=20
constant value (a small variable amount for recording where the image will =
be=20
stored in extents). 12 bytes per page is 3MB/1GB. If swsusp was to add=20
support for multiple swap partitions or writing to files, those requirement=
s=20
might be closer to 5MB/GB. Bitmaps, in comparison, use ~32K/GB (approx=20
because it depends whether the gigabyte is all in one zone). Proportionally=
,=20
bitmaps are eating a lot less space out of your gigabyte, but I don't think=
=20
anyone is going to notice that they have 3 or 4MB more cache per gigabyte=20
with Suspend2 than they have with swsusp).

Regards,

Nigel

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