Hi.

On Friday 06 July 2007 13:54:15 Benjamin Herrenschmidt wrote:
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> On Fri, 2007-07-06 at 09:35 +1000, Nigel Cunningham wrote:
> >=20
> > Nice try :) Okay then, you remove the freezer, try hibernating, then ge=
t=20
back=20
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> > to me after you've fixed your filesystem because some process that wasn=
't=20
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> > frozen started writing things after the atomic copy (making the on disk=
=20
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> > filesystem inconsistent with the snapshot).
> >=20
> > As Pavel rightly said, you can get rid of the freezer, but you're only=
=20
going=20
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> > to have to implement another one that does the essentially the same thi=
ng,=20
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> > even if it is at some other level.
>=20
> I was mostly talking about STR... Regarding STD, we have a different
> problem and we all know it. The freezer is one somewhat horrible way to
> get it working for now, I would prefer something more along the way that
> blocks the page cache from writing out new dirty pages though, except
> those specifically flagged by the snapshot.
>=20
> That is, some kind of proper snapshotting facility, as linus was
> describing some time ago.

The kind of thing Linus was talking about would limit you (as swsusp and=20
uswsusp do now) to only half the amount of memory. I suppose you could lzf=
=20
compress as you did the snapshot. That would generally get you up to 2/3rds=
,=20
but then again you can't know what compression ratio you'll get until you=20
try, so reliability would suffer or it would take longer because of retryin=
g.

I/O from swsusp and suspend2 use bios directly, so the page cache isn't an=
=20
issue for them (apart from the fact that Suspend2 saves the page cache=20
separately so it can get a full image). Not sure about uswsusp.

Only having half the amount of memory doesn't sound like a big limitation f=
or=20
modern desktops & laptops, but don't forget that there are embedded guys=20
wanting to hbernate too :)

Regards,

Nigel
=2D-=20
Nigel Cunningham
Christian Reformed Church of Cobden
103 Curdie Street, Cobden 3266, Victoria, Australia
Ph. +61 3 5595 1185 / +61 417 100 574
Communal Worship: 11 am Sunday.